Formation of organic compounds. Formation of organic substances Formation of organic substances
As you know, all substances can be divided into two large categories - mineral and organic. Many examples of inorganic or mineral substances can be cited: salt, soda, potassium. But what types of connections fall into the second category? Organic substances are present in any living organism.
Squirrels
The most important example organic matter are proteins. They include nitrogen, hydrogen and oxygen. In addition to them, sometimes sulfur atoms can also be found in some proteins.
Proteins are among the most important organic compounds and they are the most commonly found in nature. Unlike other compounds, proteins have certain characteristic features. Their main property is a huge molecular mass. For example, the molecular weight of an alcohol atom is 46, benzene is 78, and hemoglobin is 152,000. Compared to the molecules of other substances, proteins are real giants containing thousands of atoms. Sometimes biologists call them macromolecules.
Proteins are the most complex of all organic structures. They belong to the class of polymers. If we look at a polymer molecule under a microscope, we can see that it is a chain consisting of simpler structures. They are called monomers and are repeated many times in polymers.
In addition to proteins, there are a large number of polymers - rubber, cellulose, as well as ordinary starch. Also, a lot of polymers were created by human hands - nylon, lavsan, polyethylene.
Protein formation
How are proteins formed? They are an example of organic substances whose composition in living organisms is determined by the genetic code. In their synthesis, in the overwhelming majority of cases, various combinations are used.
Also, new amino acids can be formed already when the protein begins to function in the cell. At the same time, only alpha-amino acids are found in it. The primary structure of the described substance is determined by the sequence of residues of amino acid compounds. And in most cases, the polypeptide chain, during the formation of a protein, twists into a helix, the turns of which are located closely to each other. As a result of the formation of hydrogen compounds, it has a fairly strong structure.
Fats
Fats are another example of organic matter. A person knows many types of fats: butter, beef and fish fat, vegetable oils. In large quantities, fats are formed in the seeds of plants. If a peeled sunflower seed is placed on a sheet of paper and pressed down, an oily stain will remain on the sheet.
Carbohydrates
No less important in wildlife are carbohydrates. They are found in all plant organs. Carbohydrates include sugar, starch, and fiber. They are rich in potato tubers, banana fruits. It is very easy to detect starch in potatoes. When reacted with iodine, this carbohydrate turns into Blue colour. You can verify this by dropping a little iodine on a potato slice.
Sugars are also easy to spot - they all taste sweet. Many carbohydrates of this class are found in the fruits of grapes, watermelons, melons, apple trees. They are examples of organic substances that are also produced under artificial conditions. For example, sugar is extracted from sugar cane.
How are carbohydrates formed in nature? by the most simple example is the process of photosynthesis. Carbohydrates are organic substances that contain a chain of several carbon atoms. They also contain several hydroxyl groups. During photosynthesis, sugar inorganic substances formed from carbon monoxide and sulfur.
Cellulose
Fiber is another example of organic matter. Most of it is found in cotton seeds, as well as plant stems and their leaves. Fiber consists of linear polymers, its molecular weight ranges from 500 thousand to 2 million.
In its pure form, it is a substance that has no smell, taste and color. It is used in the manufacture of photographic film, cellophane, explosives. In the human body, fiber is not absorbed, but it is a necessary part of the diet, as it stimulates the work of the stomach and intestines.
Substances organic and inorganic
You can give many examples of the formation of organic and second always come from minerals - inanimate which are formed in the depths of the earth. They are also part of various rocks.
Under natural conditions, inorganic substances are formed in the process of destruction of minerals or organic substances. On the other hand, organic substances are constantly formed from minerals. For example, plants absorb water with compounds dissolved in it, which subsequently move from one category to another. Living organisms use mainly organic matter for food.
Causes of Diversity
Often schoolchildren or students need to answer the question of what are the reasons for the diversity of organic substances. The main factor is that carbon atoms are interconnected using two types of bonds - simple and multiple. They can also form chains. Another reason is the variety of different chemical elements that are included in organic matter. In addition, diversity is also due to allotropy - the phenomenon of the existence of the same element in various compounds.
How are inorganic substances formed? Natural and synthetic organic substances and their examples are studied both in high school and in specialized higher education. educational institutions. The formation of inorganic substances is not as complex a process as the formation of proteins or carbohydrates. For example, people have been extracting soda from soda lakes since time immemorial. In 1791, the chemist Nicolas Leblanc suggested synthesizing it in the laboratory using chalk, salt, and sulfuric acid. Once upon a time, soda, which is familiar to everyone today, was a fairly expensive product. To carry out the experiment, it was necessary to ignite common salt together with acid, and then calcinate the resulting sulfate together with limestone and charcoal.
Another is potassium permanganate, or potassium permanganate. This substance is obtained in industrial conditions. The formation process consists in the electrolysis of a potassium hydroxide solution and a manganese anode. In this case, the anode gradually dissolves with the formation of a violet solution - this is the well-known potassium permanganate.
Plant and animal remains accumulating on the surface of a weathered rock and in its more or less upper horizons can be observed by us in a wide variety of stages of decomposition or 1) in the form of slightly decomposed remains that accumulate over time in the form of various “felts” (in forests - “forest felt”, in the steppes - “steppe”), characterized by such a low decomposition of their constituent components that we can easily distinguish between individual parts of plants or animals; or 2) in the form of parts of plants (and animals) that have more or less already lost their original form and appearance; they appear to us then in the form of separate fragments, deformed to varying degrees, browned, having a delicate, crumbly texture and structure. Ho, and at this stage of decomposition, we can separate them from the mineral particles of the rock by various mechanical methods - by elutriating them, as they are lighter in water, sometimes by selecting them with tweezers, etc.; finally, 3) in the further stage of their decomposition, the described remains completely lose their original properties and enter into such a close chemical combination with the mineral substance of the rock that they are already inseparable from the latter by any mechanical methods.
This stage of decomposition is characterized, as it were, by the complete assimilation of the resulting products by the mineral basis of the rock; we can separate these products from the mineral part only by applying energetic chemical methods or by destroying these products (by burning).
The result of such a close chemical combination of the decomposition products of plant and animal remains with the mineral part of the weathered rock is a complex of special, so-called "organo-mineral" compounds that accumulate in the soil in one quantity or another, are distinguished by the comparative stability and strength of their composition and give the soil more or less less dark color. This group of products, which is, as it were, an integral part of the soil, “assimilated” and chemically bound by it, is called soil humus (humus).
From what has been said above, it clearly follows that not every organic compound that can be found in the soil should belong to the category of humus, or humus, soil compounds. Thus, "free" carbohydrates, fats, etc., which can be formed in the soil as a result of the decomposition of plant and animal residues, do not yet represent that organomineral neoplasm that we call humus. Owing to the abundant microflora present in soils, and owing to the diverse enzymes present in soils, the said organic compounds usually undergo such rapid and easy transformations that they can be called, in the literal sense of the word, fleeting and transient compounds. Indeed, direct analysis usually shows an extremely variable and variable amount of them in the same soil - over often even a very short period of time. These compounds, as a result of complex reactions of interaction with the mineral substance of the soil, can, of course, become inalienable in their subsequent fate. integral part soil humus, but they can, without finding the appropriate physical and chemical conditions for this, and not be part of the newly formed organo-mineral complex and remain "free", not being components of humus.
As for those mineral compounds that are always part of plant and animal remains, when the latter decompose, these compounds also suffer a double fate: some of them are freed from that strong and complex connection, in which they were during the life of one or another organism with organic compounds of the latter, and falls out in the surface horizons of the soil in the form of various "pure" mineral formations (there is, as they say, "complete mineralization of organic residues"); the other part also takes a direct part in the synthesis and construction of that organo-mineral complex, which we are now talking about.
Thus, not all mineral constituents of the soil and not all of its organic compounds are constituents of its humus complex.
From the category of soil humic substances we must also exclude those remains of decomposing plants and animals, even if severely deformed, that we can separate from the soil mass by mechanical means (remains of the root system, scraps of leaflets, remains of insect chitinous covers, etc.). ).
Thus, we distinguish between the concept of "organic component" of the soil from its "humus part". The second concept is a part of the first. This consideration must be kept in mind in all our subsequent exposition.
The chemical constitution of this complex complex, which is called soil humus, or humus, is still very poorly elucidated, despite the fact that the study of this object began a very long time ago. The main reason for this lack of study is the fact that reliable methods have not yet been developed to somehow individualize this complex object, there are still no ways to obtain it in a crystalline form, etc.
Recent years, however, have been marked by a whole series of studies that have significantly advanced the study of this complex.
Between the nature of the organic compounds that make up all the above categories of objects in a natural setting, we observe, of course, a number of gradual transitions, both between the primary minerals of the parent rock and the final products of their decay, and between the unaffected processes of decomposition of plant (and animal) ) residues and the final phases of their destruction, we can observe in each soil a number of the most diverse intermediate formations.
If at the initial stages of weathering of rocks and minerals the dominant role is played by elements of "inanimate" nature, i.e., elements of the atmosphere and hydrosphere, then in the subsequent stages of the development of these processes, when these rocks acquire the ability to provide life for the vegetation that settles on them and in connection with these begin to be enriched with the decomposition products of the latter, such a role passes to the elements of the biosphere. The fact that micro-organisms, in particular, play a leading role in the processes of decomposition of dying organic residues, was proven as early as 1862 by the brilliant research of Pasteur.
Numerous experiments with the aim of elucidating the effect of high temperatures and various antiseptic agents on the decomposition of organic substances subsequently finally established this position. It should be noted, however, that some of these experiments showed that under the above conditions the decomposition processes did not completely stop, but were only significantly suppressed, which makes it possible to assume that these processes, although to a very negligible degree, can still sometimes go in force purely chemical interaction pieces of decaying material. In any case, the last category of phenomena should be assigned a more than modest role in the processes of decomposition of organic substances.
If the processes of decomposition of organic substances in the soil are mainly biochemical processes, then it is clear what various forms and directions these processes can take in the soil under natural conditions, depending on one or another air supply, soil moisture, temperature conditions, chemical and physical properties environments, etc.
In order to understand how far the decomposition of organic residues can go in each individual case and at what intermediate stages this decomposition can be delayed in each individual case, we will further consider the significance in these processes of each of the factors mentioned above separately, moreover, without citing of all the numerous literature available on this issue, we confine ourselves to reporting only the final conclusions obtained in this area.
The starting point for the research presented here is the well-known position that the selection carbon dioxide from decaying organic matter can be recognized as a measure of the speed and energy of this decomposition (Hoppe-Seuler). Taking into account, however, that in the soil, in parallel with the processes of decomposition of organic substances, under the influence of the vital activity of microorganisms, processes are often reversed - synthetic - and, therefore, the amount of carbon dioxide released cannot always serve as a measure of the decomposition of organic matter, one can resort to another research method, namely, directly to the analysis of the amount of mineral compounds that are split off from the decaying substance included in its composition.
Of the main conditions that determine the rate and nature of the decomposition of organic substances, we will focus on studying the influence of temperature, degree of moisture, degree of air inflow, chemical properties of the medium, and the nature of moisture entering the decomposing material on these processes.
Influence of temperature and humidity. The most detailed research on this issue was carried out by Wollny.
The decomposing material was placed in U-shaped tubes and air devoid of carbon dioxide was passed through them. These tubes were placed in water baths, where the temperature was adjusted as desired.
If the humidity of the taken object remained constant, then the amount of carbon dioxide (CO2) increased with increasing temperature. So, the air passing through the tubes contained carbon dioxide (in compost soil):
If, in turn, the temperature remained constant and the degree of humidification increased, then the amount of CO2 also increased accordingly:
Thus, both the temperature and humidity of the decomposing substrate affect the process of interest to us in one direction.
Changing the conditions of temperature and humidity in opposite directions in his experiments, Wollny came to the conclusion that the formation of CO2 occurs most intensively under average conditions of temperature and humidity. So, for example, when
Similar results were obtained by Fodor, whose research is also of interest because he worked, among other things, with very high temperatures (up to 137 °). All his experiments fully confirmed Wollny's conclusions; among other things, he stated that at very high temperatures, the release of carbon dioxide from the decomposing mass, although it continued, was extremely weak. Further studies by Petersen with the decomposition of organic matter in the black earth and with the decomposition of the wood of deciduous trees, as well as by Bellen and the late P. Kostychev - with fallen birch leaves, fresh spruce needles and hay, showed in general that both temperature and humidity really act in the same direction. , but up to a certain limit (in the direction of increase or, conversely, in the direction of decrease), when the vital activity of microorganisms was already disrupted due to this, and when the process, in connection with this, moved forward very weakly and sluggishly.
The final conclusion from all these observations can be formulated as follows: the decay energy of organic substances reaches an optimum at a certain average humidity and temperature. The lack of humidity lowers this energy, as well as its excess, because in the latter case, the free circulation of air is hindered in the decomposing mass. Low and high temperature also inhibit the described process.
The results of all these experiments and observations, transferred to the natural environment, help us in the best possible way to understand the reasons for the accumulation in this or that area of this or that amount of humus - of this or that composition. In each individual case, we can always associate these phenomena, on the one hand, with the climatic conditions of the given area and with those factors on which the microclimatic situation depends (landscape, nature of vegetation, etc.), physical and chemical properties the soil itself (in this case, its water and thermal properties), through which all the elements of the nature surrounding this soil are refracted.
Influence of the chemical properties of the medium. We will limit ourselves to only the most general provisions that exist in this area.
The acidity of the environment, according to the experiments of Wollny and many other researchers, has a depressing effect on the processes of decomposition, which, of course, is quite understandable if we recall that for the bacterial population - this main causative agent of the processes we describe, the acidic environment is a poison (fungal microflora, however, to this factor up to a certain limit, as we know, is insensitive).
As for the significance of the alkaline medium, we will dwell on this issue a little closer, and we will keep in mind the effect on the processes of interest to us only of the presence of calcium carbonate, because it is with this compound that we most often have to deal when discussing, for example, the question of the influence on the energy of decomposition of organic matter of such common parent rocks as loess, loess-like loam, etc. formations rich in calcium carbonates.
Not so long ago there was a belief that CaCO3 (calcium carbonate) significantly accelerates the rate of decomposition of organic matter. In practice Agriculture until recently, the position was widespread that “lime, enriching the fathers, ruins the children”, i.e. that this substance contributes to the extremely rapid decay of humus in the soil, the “dropped out” nutrients from which (the mineral compounds contained in it) temporarily they greatly increase the fertility of the soil, but at the same time deprive the soil of that supply of these compounds from which subsequent crops could draw their food. This erroneous belief was based, among other things, on Petersen's research.
Petersen set up his experiments with soil that had 58% humus (i.e., with soil clearly acidic), and by the amount of CO2 he stated almost a triple amount of this gas when calcium carbonate was added to this soil, from which the mentioned author concluded that lime significantly accelerates the decomposition of organic matter. In another experiment, Petersen operated with calcareous soil - unmodified, and also with the same soil, but previously treated to remove lime. hydrochloric acid. The results were the same. The first experiments of the mentioned scientist were later subjected to fair “criticism by the late P. Kostychev, who drew attention primarily to the fact that the soil with which Petersen manipulated was undoubtedly acidic, containing a lot of free humus acids. It is clear that the addition of calcium carbonate to such a soil, averaging the medium, created favorable conditions for decomposition processes. As regards another group of experiments by Petersen, the latter missed the effect of pre-treatment of the soil with hydrochloric acid, which was supposed to have a detrimental effect on the soil bacterial flora.
Further experiments by P. Kostychev with tree foliage and with chernozem soils showed that the addition of calcium carbonate, on the contrary, always lowered the energy of decomposition. Similar results were obtained by Wollny, Reitmair, Kossovich and others. Only in exceptional cases, when the soil medium contains a lot of free humus acids, the addition of lime can promote decomposition processes.
As is known, the humus enrichment of chernozem soils is partly explained by the protective role played by calcium compounds, which are part of the parent rocks most common in the steppe zone (loess, loess-like loams, etc.).
Taking into account that calcium is an energetic coagulator of colloidal substances (both organic and mineral), we must also attribute to this element the role of an energetic fixer of humus compounds in the soil layer. The loss of soil, for one reason or another, of calcium compounds entails, as is known, the processes of its complete degeneration ("degradation") - with the loss of part of the humus substances by washing out, etc.
Influence of air inflow on the decomposition of organic substances. To elucidate the role of air as one of the factors in the decomposition of Wollny organic substances, the following experiment was carried out: a mixture of quartz sand and peat powder, moistened to a certain limit, was placed in U-shaped tubes through which air with different oxygen contents was passed, as well as pure nitrogen and pure oxygen. The amount of carbon dioxide was determined every 24 hours. The results of the experiments showed that the decomposition of organic matter increases with an increase in the percentage of oxygen in the air. On the contrary, with a decrease in the latter, and even more so with the replacement of this gas by some indifferent gas (for example, nitrogen), the oxidation of carbon in organic matter was strongly inhibited. The lack of oxygen flowing to the decomposing material affects not only the decrease in the energy of this decomposition, but is also reflected in the very nature of the process. From this point of view, it is customary to distinguish between the process of decay (i.e., the process of decomposition with air access) and the process of decay (i.e., decomposition under anaerobic conditions).
If organic residues decompose with full access to air (the aerobic process is the “smoldering process”), then these processes are purely oxidative in nature, and the decomposition of organic matter can proceed unceasingly (in the absence, of course, of any factors inhibiting these phenomena) up to such products like water, carbon dioxide, salts of nitric, sulfuric, phosphoric and other acids. At the same time, the mineral substances that were part of the ash elements of the decaying residues are thus, as it were, released. There is a "mineralization" of organic residues.
Smoldering usually occurs with a significant release of heat.
During anaerobic processes (“rotting process”), we state a number of incompletely oxidized compounds, such as methane (as a result of anaerobic methane fermentation of cellulose, starch, pentosans, etc.), hydrogen sulfide (a characteristic product of protein decay), hydrogen (a product of hydrogen fermentation of cellulose), hydrogen phosphorous, ammonia, nitrogen, etc. Further, among the products of anaerobic decomposition, we see such intermediate forms of protein decomposition as indole, skatole, etc. Finally, in the decomposing mass, numerous organic acids are formed under the described conditions - fatty acids ( starting with formic and ending with oil with its higher homologues), then lactic acid, benzoic, succinic, etc. Organic acids gradually accumulating in large quantities, not finding favorable conditions for their further decay due to lack of air, stop the development of microorganisms, and further decomposition organic matter can completely stop.
Smoldering and decay are, of course, only the most extreme forms of decomposition of organic matter, between which various intermediate stages are possible.
Influence of the nature of moisture inflow to a decomposing substance. In addition to the factors listed above, the energy and nature of the decomposition of organic substances is influenced very sharply by the nature of the supply of moisture to the decomposing substance (S. Kravkov). In a direct study of the amount of mineral compounds that are split off from various decaying plant residues in the case when these residues systematically experience through washing with water (i.e., when the decomposition products are constantly removed from the sphere of interaction with each other), and in the case when these products always remain in interaction with the decomposing material, it was stated that in the first case, in the decomposing mass, acidic products accumulate in abundance, inhibiting the further course of decomposition processes, in the second, these processes, on the contrary, proceed very vigorously all the time. A closer study of this phenomenon showed that during the through washing of a decomposing material, we are dealing with a very rapid loss of its alkaline earth bases by this substance, which contributes to the accumulation of unsaturated acidic products in the decomposing mass, which inhibit this process.
The same phenomena were ascertained by S. Kravkov in relation to soils. These conclusions, stated back in 1911, are best explained today from the point of view of the teachings of K. Gedroits about the “soil absorbing complex.
The described facts must be kept in mind when studying the conditions of accumulation and decay of organic substances in soils with different water-permeability, lying in different relief conditions, etc.
In addition to the factors discussed above, a number of other conditions also have an important influence on the energy of decomposition processes: the degree of fineness of the decomposing material (the higher the sleep, the greater the surface of contact with atmospheric agents: temperature, moisture, air oxygen, etc., decomposition processes proceed more energetically), the chemical composition of the decomposing material (protein substances, sugars, some organic acids are most rapidly decomposed; more difficult - cellulose, lignin, cork substances; finally - resins, waxy substances, tannins, etc.). From this point of view, knowledge of the chemical composition of those plant associations that take part in each individual case in the creation of the organic matter of this or that soil seems to be absolutely necessary.
Transferring all these conclusions to nature, we can already foresee that the nature and energy of the decomposition of organic substances must represent an even more sensitive reaction to a change in one or another external factor in one direction or another than the processes of weathering of minerals and rocks discussed above. Reality fully confirms this assumption: the amount of humus accumulating in a particular soil, its qualitative composition, chemical properties, etc. can always be closely linked with the nature of the surrounding climatic conditions, with the relief conditions, with the nature of the plant (and animal) world, and, finally, with the characteristics of the parent rock and with the whole complex of internal physico-chemical and biological properties of the soil itself.
Having considered the conditions on which the energy and nature of the decomposition of dying organic residues depend, we now turn to the study of the chemical composition and properties of the products of this decomposition.
Just as in the mineral part of the soil, we distinguish, on the one hand, relics (remains) of primary minerals and rocks that pass into the soil without a significant change in their internal chemical nature, and on the other hand, a number of various intermediate products of their weathering up to relatively difficult their representatives undergoing further change (at different stages of soil development - different in composition and properties), so in the organic part of soils we can also find a gradual range of transitions from "primary" organic compounds that are part of the dead plant remains untouched by decomposition processes and animals, to such organic compounds, which, in relation to the mentioned category of substances, could also be called "new formations" and which could also be recognized, on every this stage soil development, relatively weakly amenable to further decay.
Among the decay products of organic substances, which are characterized by relatively high stability, we must include those humic substances that were mentioned above. Their stability explains relatively weak fluctuations over a certain period of time. quantitative composition humus in one or another soil type, in one or another of its differences. Ho, of course, in the process of evolution that every soil undergoes, these substances inevitably also take an active part - up to even their complete destruction and subsequent mineralization, that is, until the mineral compounds fall out of them - in a free form, and until the transformation " organogens” into such end products as CO2, H2O, etc.
Leaving aside the consideration of the composition and properties of those transient and "fleeting", and therefore inconsistent and uncharacteristic products of decomposition, which we spoke about above, we will turn further to the study of that specific soil formation, which is called humus.
Soil humus compounds, which play such a paramount role in soil formation and in plant life, have long attracted the attention of numerous investigators. Despite this, it is still not possible to fully understand the entire complex of phenomena associated with the genesis of humus, its composition and properties.
In order to understand the composition and properties of soil humus, the analytical path has long been used: various attempts have long been made to isolate this complex complex from the total soil mass in one way or another, followed by an analysis of its composition and properties.
The method of extracting humic substances from the soil, proposed by Sprengel and which has not lost its significance in the Grandeau modification to this day, consists in treating the soil with some kind of alkali carbonate (sodium carbonate, potassium carbonate or ammonia carbonate). By prolonged and repeated washing of the soil with the mentioned reagents, it is often possible to achieve almost complete discoloration of this soil and obtain a black or brown liquid in the filtrate, which is thus an alkaline solution of humus substances of the soil under study (“black substance”). In view of the fact that, in a certain part, those mineral substances of the soil that do not belong directly to humus compounds (in the form of the thinnest suspensions) can get into the solution of the “black substance”, the filtration mentioned above is currently usually carried out using special filters that can completely delay these suspensions (using, for example, Chamberlain clay candles, etc.).
As studies have shown, it is still not possible to isolate all humus compounds in this way: no matter how long and repeatedly we treat the soil with carbonic alkalis, the latter almost always contains a certain amount of organic substances that cannot be dissolved and excreted. There are indications in the literature that in some soils there are from 15 to 30 and even 40% of the total mass of organic substances present in these soils, which, of course, indicates the extreme importance and urgent need for the nearest examination. and this non-extractable part of the soil humus. Previous researchers called these compounds, which are not decomposed by alkalis, "indifferent" substances of soil humus (humin - darker in color, ulmin, hein, etc. - brownish).
The process of conversion of part of the humic substances of soils into an alkaline extract, as discussed above, was usually considered as the formation of soluble alkaline salts of various humic acids.
In this acidic part of soil humus, former researchers distinguished: 1) ulmic acid, 2) humic acid, 3) horseradish acid (key) and 4) apocrenic acid (sedimentary-key), and it was believed that ulmic and humic acids are the least oxidized part of the soil humus, that is, they are the youngest and most initial form the decay of certain organic compounds that took part in its synthesis; crenic acid is a product already more oxidized than those mentioned above; finally, apocrenic acid is an even more oxidized substance, characterizing an even deeper decomposition of those organic compounds that take part in the construction of soil humus. Each of the above-mentioned alleged components of humus was considered to be a specific chemical individual and was clothed by various authors in various specific chemical formulas.
The components of soil humus listed above have, according to a number of researchers, the following properties:
Humic acid (and close to it ulmic) - black; extremely slightly soluble in water. Its salts ("humates") - sesquioxides, as well as salts of calcium, magnesium and ferrous oxide are also insoluble. Soluble are only its alkaline salts (potassium, sodium, ammonium).
Crepe acid ("key" acid) - easily soluble in water; its aqueous solution is colorless. Its salts ("krenates") - alkaline, alkaline earth and ferrous oxide salts - are easily soluble. The same must be said about the acid salts of alumina; salts of sesquioxides - medium, as well as manganese and copper - are hardly soluble in water.
Apocrenic acid ("sedimentary-key" acid) is somewhat less soluble in water than crenic acid. Its salts (“apocrenates”) of alkalis and ferrous oxide are easily soluble in water; salts of alkaline earth bases - somewhat more difficult; salts of sesquioxides, manganese and copper salts are hardly soluble.
The described properties of the soil humus components are also the basis for the existing methods for their separate production.
The idea of humus as a complex of various, definite composition of acids and their salts is also supported by a number of modern researchers. So, Sven-Oden distinguishes the following compounds in the composition of soil humus:
Humus coals (corresponding to ulmin and humin of former authors). They are anhydrides of "humic" and hymatomelanic acids. They are insoluble in water and do not give colloidal solutions. Covered in black or dark brown.
Humic acid; corresponds to the humic acid of the previous authors, with all its properties (it is very slightly soluble in water and alcohol; all its salts, except alkaline ones, are also insoluble; it can give colloidal solutions with water; the acid is black-brown in color).
Hymatomelanic acid; corresponds to the ulmic acid of the former authors. Brown color. Similar in properties to humic acid, but soluble in alcohol. With water gives colloidal solutions.
Fulvic acids correspond to crepe and apocrenic acids of the previous authors. Easily soluble in water, like most of their salts. Painted yellow.
Thus, Sven-Oden, on the basis of his research, admits that the humus substances of the soil are indeed certain chemical compounds (acids and their derivatives), but partially, being in a colloidal state, they can also give the so-called "absorbent compounds".
In parallel with attempts to elucidate the very nature of the components that make up the humus substance of the soil, active research work has been going on for a long time to elucidate internal structure this complex complex. Particular attention was drawn to the question of the nature and strength of the connection with the "core" of humus of ash substances and its nitrogenous compounds.
On the basis of some works, one can think that the organo-mineral compounds that make up soil humus are simple and double salts of humic acids, where ash substances are associated with organic substances like the bonds of bases with acids, thus obeying the laws of simple chemical reactions ( Schibler, Mulder, Pitch). On the other hand, there is evidence that ash substances are much more firmly embedded in humus and cannot be completely extracted from last way processing it by conventional methods, but only after its complete destruction (for example, by burning). We have indications of this from previous authors. So, for example, Rodzianko, after repeatedly re-precipitating humus and treating it with 30% hydrochloric acid, nevertheless found about 1.5% ash in it. All these studies give reason to think that minerals are present in the molecule of the humus complex itself.
According to a number of scientists (Gustavson), in addition to acidic aqueous residues, humic matter also contains alcohol residues, the hydrogen of which can be replaced by metals with a weak acid character (iron, aluminum). It is precisely these polyatomic metals that are found in the ash of the humic substance, and they can be links between the rest of the mineral part of the mineral compound (P2O5, SiO2, partly saturated with other bases) and organic substances. Such a compound should not be decomposed by alkalis, because, as is known, the hydrogen of alcoholic aqueous residues cannot be replaced by radicals with an alkaline character.
Further, the works of Hoppe-Seyler, which showed that humus substances with caustic alkali and water, when heated to 200 ° C, give protocatechinic acid (one of the dioxybenzoic acids), suggest that phenolic aqueous residues are present in the humus complex (confirmed latest research- F. Fischer).
Reinitzer, having stated the ability of humic acid to restore Fehling's liquid, tends to think that it also contains an aldehyde group, or a hydroxyl group, as in phenol, or both. There are certain indications of the presence of carboxyl groups in the composition of humic acid. Levakovsky, P. Slezkin, S. Kravkov believe that the bond in humus between the organic and mineral parts is as strong as it exists in fresh plant matter, and that tumus receives part of its ash parts, as it were, “inherited” from the humus former. From this point of view, the ash substances of humus enter the very molecule of organic matter, and the humus complex enters the soil from dying plant (and animal) residues to some extent in a “ready” form, i.e. not in the form of a purely organic, but mineral -organic matter, as if finishing later, when it enters the soil, its final formation by adding a number of other ash elements already from the soil. We find some confirmation of this view in the later works of B. Odintsov and Gartner, who obtained extracts from decaying plant residues that are very similar in composition and properties to soil humus.
A large number of studies were devoted to a more particular question - in what form is nitrogen in soil humus. There is evidence that this element is partially present in humus in the form of ammonia compounds, which is proved by the possibility of removing these compounds by boiling humus substances with caustic alkalis and re-precipitating with acids. Tenar, from heavily rotted manure, extracted acid, which, after 10-fold dissolution in KHO and precipitation with acid, did not lower the nitrogen content; hence the author concluded that this nitrogen is not ammoniacal, but belongs to a particle of the acid itself and can be displaced from there only when the substance is completely destroyed, for example, when fused with caustic alkali, etc. Studies by a number of other scientists also stated the presence in soil humus some - not studied closer - very strong nitrogenous compounds. The works of Berthelot, Andre showed that nitrogen in soil humus is in its known part in the form of amides and amino acids. At the same time, the experiments of the last of the authors we named showed that, in addition to amide and amino acid (and ammonia) nitrogen, soil humus contains some (from 20 to 66% of the total amount of nitrogen) amount of this element in some form ( in which one, remained unclear), not decomposed by either alkalis or nitrous acid. Some researchers consider this stable nitrogenous part of humus to be the remains of substances of animal origin (keratin, quinine, etc.). The late P. Kostychev considered these nitrogenous substances to be part of living bacteria and fungi living on soil humus. There is an assumption (Demyanov) that there are protein substances in humus, but not in a free form (in which they are fragile and easily decomposable - both from chemical reagents and under the influence of enzymes), but in a stronger combination with other acidic substances, for example , with tannic and phosphoric acids and, finally, with nitrogen-free humic acids or with dehydrated vasculosis. There are good reasons to suspect the presence in soil humus of nitrogen belonging to nucleins, nucleoproteins, lecithin, etc. The presence of protein in soil humus is confirmed by the works of A. Shmuk.
Te successes that have been achieved, especially for last years, colloidal chemistry, could not but be reflected in some provisions of soil science and, in particular, could not but play significant role and in elucidating the true nature of humic substances. The works of van Bemmelen, Fischer, Ehrenber g, and the outstanding research of the Russian scientist K. Gedroits now enable us to consider the humic substances of the soil as compounds, to a certain extent, in a colloidal state. We are led to this by the study of a whole series of peculiar properties possessed by these substances. So, their ability to coagulate from solutions under the influence of acids and salts, frost and electric current, the strongest absorption of water by them and - as a result of this - the strongest ability to swell, and after drying, the strongest decrease in volume, very weak electrolytic conductivity, the subordination of the transformations undergone by humic substances to the laws of surface tension, and not to stoichiometric laws, the ability of humus substances to precipitate sols of oppositely charged colloids, the ability to form complex mixtures and complex addition products, etc. - all this confirms that in the face of humus substances we see a complex complex of compounds that are in a certain part in a colloidal state.
From this point of view, some of the properties of humic substances considered above should be drawn to us in a somewhat different form. So, the ash, for example, part of humus substances should be considered not as any specific chemical compound, but as an “absorbent compound”; solutions of humic substances in alkalis should not be true solutions, but pseudo-solvents, which are the precipitating effect on humic substances of two-valued and three-valued cations (Ca ++, Mg ++, Al +++, Fe +++) - as a process of coagulation, coagulation, formation of gels, etc. According to W. Gemmerling, the dispersity of humus substances increases in parallel with their degree of oxidation and in parallel with their activity. From this point of view, W. Gemmerling considers humin and ulmin to be the least dispersed bodies, and crepe and apocrenic acids are the most dispersed.
In the works of Baumann and Gully, however, the above views of van Bemmelenn others have found an extreme expression; the mentioned authors tried to prove that humic acids never form real salts at all, that all the compounds that were described as salts actually have neither the constancy of composition nor the ability to ionic reactions, being exclusively "absorption (adsorptive) compounds." At present, we must consider these views exaggerated, because, as we indicated above, only a part of humic substances can be in the colloidal state in the soil; in addition, it should be noted that the colloidal state of matter does not exclude the ability of the substance to enter into chemical reactions.
On the basis of a number of later studies, one has to consider that none of the "acids" mentioned above is a specific chemical individual, but, taken individually, is a complex complex of various compounds. From this point of view, the existing methods for the separation of soil humus into the above components should be considered conditional, meaning by the word "humic", "crepe" and "apocrenic" acids only a set of homogeneous in their physical and chemical properties complexes.
We have indications of this from earlier authors (Post, Muller, Reinitze, Berthelot, and others), who stated that the organic part of soils contained the existence of a number of very diverse organic compounds (resins and fats, glycerol, nucleins, aldehydes, and many others). ); However, this provision received a particularly strong justification after the work of American scientists (Schreiner and Shorey and others). The latter, in order to study the composition and properties of humus compounds, applied to various American soils a whole series of the most diverse reagents - in order to extract from the soils the most diverse groups of organic compounds that could be found in the humus of these soils. For this purpose, they used caustic alkali, mineral acids, alcohol, petroleum and ethyl ether, etc. as solvents. ).
Of the acids found were: monooxystearic, dioxystearic, paraffinic, lignoceric, agroceric, oxalic, succinic, crotonic and other acids.
From carbohydrates were found: pentosans, hexose, etc.
From hydrocarbons: entriacontane.
From alcohols: phytosterol (from the group of cholesterol substances), agrosterol, mannitol, etc.
From esters: esters of resin acids, glycerides of capric and oleic acids, etc.
From nitrogenous substances: trimethylamine, choline.
Diamino acids: lysine, arginine, histidine, etc.
Cytosine, xanthine, hypoxanthine, creatine.
Picolinecarboxylic and nucleic acids.
In addition to the compounds mentioned, benzoic acid, vanillin and many others have been isolated in many soils. others
Of all the listed substances in humic acid (i.e., in the precipitate formed during the treatment of an alkaline extract with hydrochloric acid), the following prevailed; resin acid esters, resin acids, fatty acid glycerides, agrosterol, phytosterol, agroceric, lignoceric, paraffinic acids, etc.; in the composition of crenic and apocrenic acids (i.e., in the acid filtrate from the sediment mentioned above), the following were found: pentosans, xanthine, hypoxanthine, cytosine, histidine, arginine, dioxystearic and picolinecarboxylic acids, etc.
It is interesting to note that with repeated treatment of soils with caustic alkali (2%), the latter still contained a significant amount of some organic compounds that did not pass into solution (“humin” and “ulmin” by previous authors).
Of course, there is no doubt now that the so-called humic, crepe, and apocrenic acids do not represent any specific chemical individuals, but are each taken separately a mixture of various organic compounds. However, the works of American researchers mentioned above do not in any way resolve the problem associated with elucidating the composition of humus, because it remains unclear whether they determined all the substances listed above in the organic part of the studied soils in general or just in the humus part of their composition (recall that distinction these two concepts, which we made above). Rather, we have to assume that all the organic compounds isolated above from soils are components of the organic part of soils in general; but which of them are part of the soil humus remains unclear. The very fact of the presence in soils of all those organic compounds that are part of plant and animal remains, as well as the presence in them of various intermediate forms of decomposition of these compounds, of course, cannot be subject to any doubt. Therefore, the studies carried out by American scientists hardly move us forward in resolving the question of the composition and properties of that organo-mineral soil neoplasm that we call humus. At best, they give us an extra argument in our hands - to suspect the chemical complexity and diversity of those complexes that we conditionally unite with the words “humic”, “crepe”, etc. acids.
In view of the fact that no methods have yet been found by which we could isolate pure humic substances from the soil and thereby individualize them, the considerations we have just expressed can be applied to a greater or lesser extent to all other studies and works. who strive to decipher the composition and properties of soil humus in one way or another by trying to isolate the latter from the soil, because we can never be sure whether we are really dealing with soil humic substances or whether we have before us only various relics of those organic compounds that were part of the dead plant and animal remains and which we must recognize as transient compounds in general of the organic part of this soil.
There is no reason to assume whether all the organic compounds determined by this method are some kind of new formations obtained in the very process of processing the studied soils with one or another reagent used (alkali, alcohol, etc.). Finally, it is impossible not to point out that the composition of humus in different soils, of course, is very different (depending on the composition of dying vegetation, on climatic conditions, on the physico-mechanical and chemical composition of the mineral part of the soil, etc.). Therefore, the desire to elucidate the composition and properties of soil humus in the way mentioned above undoubtedly encounters extremely many difficulties, giving us, in each individual case, conditional particular ideas about the data obtained.
All the considerations now expressed can be fully applicable, as we have indicated above, to those latest attempts that have been made for recent times a number of researchers in the field of finding methods for isolating humic substances from the soil mass. Particular attention is currently being drawn to the method of isolating soil humic substances by treating the latter with acetyl bromide (CH3COOBr) - a method proposed by Karrer and Boding-Wieger and widely used by Springer. Acetyl bromide, as shown by relevant studies, brings into solution all the organic substances of the soil that have not yet humified plant residues and almost does not affect the humic substances of the soil, which, it would seem, opens up wide possibilities for the subsequent direct study and analysis of these latter. However, this method is still too little studied and little tested, which is why we have to refrain from any definite judgments for the time being. All the more applicable what has been said in relation to other recent attempts to isolate humic substances from the soil - to methods, for example, soil treatment with hydrogen peroxide, pyridine, etc. We must recognize all these methods as conditional and controversial as the above method, used by Schreiner and Shorey, as a result of which all the considerations and provisions put forward by the above-mentioned researchers on the composition and properties of soil humic substances raise a number of insoluble doubts.
In view of this, we do not consider it possible to present in this course all the views expressed by the authors mentioned above on the composition, structure and properties of humic substances, as being based on unreliable and conditional grounds.
For a long time, attempts have been made to apply a different method to judging the composition and properties of humic substances, namely the synthetic method, or, more correctly, the genetic method, that is, the method of artificially obtaining humus substances (with all their characteristic properties) from certain chemical individuals in a detailed study of all those intermediate stages that these individuals go through along the way. We must recognize the path of genetic study of humus as undoubtedly more fruitful and able to quickly give us the key to resolving questions related to the origin, composition and properties of this complex complex.
On this path, two methods can be used: either one can try to artificially obtain compounds similar to humic substances by processing various organic compounds most common in the plant body with one or another reagent. This path was widely used in the work of former researchers (especially many such experiments were carried out with carbohydrates by treating them with strong mineral acids). Or, in order to avoid the use of such "violent" methods of humification of the objects under study, one can use a different method, namely: by placing certain chemical individuals (proteins, carbohydrates, etc.) and their combinations in different conditions of their decomposition (at different temperatures , under various conditions of aeration and humidification, with the participation biological factors and without them, etc.), try to investigate which of the studied objects and under what conditions can turn into substances similar to humus and which cannot, and by studying the intermediate stages that these objects go through on the way to the final formation of humus, try to penetrate and into the very essence of the chemical transformations taking place. We must recognize this path as both more natural and more productive.
The first question of a general order, arising from such a statement of the problem of interest to us, is the following: what are the constituent parts of dying plant and animal remains that are directly involved in the construction of humus? In other words: which of these constituent parts should we consider the "original sources" of the material composition of humus? Some researchers, based on the theoretical premises that only those constituent parts of plants (and animals) that have comparative stability and strength during their decomposition processes, should take part in the construction of humus, make the assumption that the main source of humus formation is fiber, encrusting substances, lignin, gum, tannins, etc. Other constituents of plant residues (proteins, etc.) during their decay processes are so easily and quickly decomposed in the soil to final products (CO2, H2O, etc.) that, according to these researchers, they cannot be fixed in the soil mass and thus cannot take part in the synthesis of that strong and stable complex, which is humus. Other researchers put forward a different point of view, which is to some extent the opposite of what has just been stated, namely, that the closest and most direct part in the formation of soil humus is, on the contrary, the most mobile and, in particular, only water-soluble decomposition products of dying organic residues (Levakovsky, Hoppe- Seyler, Slezkin, Kravkov).
Based on the work of these researchers, it can be seen that atmospheric water, even from fresh, i.e., not yet subjected to any decomposition processes, plant residues is able to wash out a number of both organic and ash compounds, which subsequently, under the influence of various physio- chemical and biochemical agents are capable of turning into dark, humus-like substances. This process, of course, takes place on an even more dramatic scale in the case when water has to act on dead plant remains that have already undergone certain stages of decay (a case that mainly has to be dealt with in natural conditions).
The contradictory judgments outlined above about the primary sources of the material composition of soil humus, we must now consider to have lost their sharpness. Now there is no longer any doubt that, before turning into humus, all-organic compounds, undoubtedly, must first pass through the liquid phase. And since absolutely stable and absolutely unchanging organic compounds do not exist, and all of them, under the influence of purely chemical or biochemical agents, can undergo various transformations, including in the direction of increasing their mobility and solubility (even lignin, resins and tannins), it is necessary to recognize that in the construction of the humus core of the soil mass, in general, all organic compounds that make up plant and animal residues can take part. The question is reduced only to clarifying the share of participation of each of the organic compounds in the process of building this core, and most importantly, to clarifying those complex chemical, physicochemical and biochemical interactions that take place between organic compounds and the mineral substance of the soil, in other words, to the study of those complex phenomena that accompany the very process of formation of the organo-mineral complex, the soil body.
Extensive research in these areas was carried out in our laboratory by A. Trusov. Putting various organic compounds - often for quite a long time - into various conditions of decomposition, the said author made, on the basis of his experiments, the following main conclusions:
1. Carbohydrates (fiber, hemicellulose, starch, sucrose, glucose and levulose) apparently do not take part in the formation of humic substances.
2. Oils take only the most limited part in this synthesis.
3. Organic acids, gums, cork also should not be classified as humus formers.
4. The main "suppliers" of soil humic substances are proteins, tannins, encrusting substances (lignin) and various polyphenolic compounds (hydroquinone, orcin, pyrogallol, etc.).
5. Protein substances on the way of their humification undergo primarily hydrolytic decomposition; further oxidation and condensation of the products of this hydrolysis occur. From such products of the hydrolytic decomposition of proteins, pyrrole and benzene compounds go to form humic substances, and from the latter - mainly containing a phenolic group, for example: indole, skatole, proline, tryptophan, phenylalanine, tyrosine, etc. Obtained are condensed, colored black and brown color products with the character of oxyquinones.
6. The humification of lignin (encrusting substances) is due to the phenolic and quinone groups contained in it. Various compacted products are obtained - again with the character of oxyquinones.
7. Hummification of tannins - through gallic acid, resulting from the hydrolysis of these substances, again goes to the formation of compacted products with the character of oxyquinones; in addition, tannomelanic acid, pyrogallol, purpurogallin, etc. are obtained.
8. Approximately the same products are obtained during the humification of polyphenolic compounds that are part of plant residues.
The humification of all the above organic compounds occurs in the soil under the influence of a wide variety of both biological and chemical factors.
Summing up all the processes of humification under one general scheme, we can thus say that the first stage of these processes is the hydrolytic decomposition of various carbon compounds, i.e., the decomposition of a complex carbon chain into simpler parts.
The second stage in the formation of humic substances is expressed in the vigorous loss of water and in the phenomena of internal compaction.
A. Trusov, as we see, was drawn only general scheme the processes we are interested in. Recently, the synthetic (genetic) way of studying soil humic substances has been widely used by the American researcher Waksman.
Based on the consideration that various organic compounds that make up dead plant and animal residues have varying degrees of resistance to the destructive action of microbes and varying degrees of their chemical mobility and reactivity, and, consequently, varying degrees of possible participation in the synthesis of that relatively stable complex What is soil humus, Waksman, having developed an appropriate technique, divides all organic compounds found in plant matter into a number of fractions that are united by some common properties.
1. If one or another plant substance (peat, etc.) is subjected primarily to extraction with ether, then they pass into the solution; essential and fatty oils, part of waxy and resinous substances, etc. This group of compounds should be characterized as having great resistance to the decomposing action of microorganisms and, as such, can, therefore, take part in the formation of that relatively strong complex, which is soil humus.
2. By acting on the residue, after treating it with ether, water (first cold, then hot), we contribute to the transition into a solution of various sugars (glucose, mannose, pentose, etc.), amino acids, some soluble proteins, some organic acids (tartaric, acetic, arabanic, malonic, etc.), alcohols (mannitol, etc.), a certain amount of starch, tannins, etc. This group of substances, with the exception of tannins, on the contrary, can be characterized as very easily degradable under the influence microorganisms (bacteria and fungi), which is why, being quickly destroyed in the soil, it does not serve as a direct source for the construction of the humus complex.
3. Further acting on the residue of the analyte with boiling "95 ° alcohol, we transfer into solution some resins and waxes, alkaloids, chlorophyll and other pigments, tannin, choline, higher alcohols (inositol), etc. All this fraction must be characterized as possessing great stability and resistance to the decomposing action of microorganisms and, therefore, can, as such, in its slightly modified form be present in the composition of soil humus.
4. By acting on the residue from the previous treatment with diluted boiling acids (for example, 2% HCl), we contribute to the transfer of hemicellulose (“fake” fiber), which undergoes hydrolysis during this operation, i.e., passes into simple carbohydrates Hemicelluloses are, as is known, both hexoses and pentoses are anhydrides (derivatives of the latter, the so-called pentosans, are very common in the plant body).
Treating the residue from the previous operation with concentrated acids (80% H2SO4 and 42% HCl), we transfer cellulose (“real” fiber) - a complex glucose anhydride, into a solution.
Both cellulose and hemicelluloses are one of the main components of the dry matter of plant residues.
Although from the chemical point of view, both mentioned groups of organic compounds should thus be characterized as very strong and stable compounds, nevertheless, under the influence of the activity of special microorganisms that secrete hydrolyzing enzymes, they undergo fairly rapid and complete decomposition in the soil, which makes it very doubtful their presence in soil humus.
5. The remainder of all previous operations gives us the opportunity to determine the so-called lignin (encrusting substances that are a necessary part of cell walls plants). The chemical nature of lignin is unclear. This is a collective concept, which includes a complex of various compounds that are not amenable to hydrolysis even under the influence of such concentrated acids as the above-mentioned 80% H2SO4 and 42% HCl. Its great resistance against the destructive action of microbes gives the right to consider it one of the usual components of soil humus.
6. The group of nitrogen-containing compounds plays exclusively important role in the life of plants and animals, entering as an integral part of the plasma of cells. This group is numerous and diverse in its properties. Some of these compounds are soluble in water (see above: soluble proteins, amino acids, etc.); the other part is easily hydrolyzed when exposed to boiling dilute acids (actually proteins) and then gives water-soluble compounds; the third part is hydrolyzed only when exposed to concentrated acids, etc.
From this point of view, the group of nitrogenous organic compounds must be recognized as very different - in terms of the degree of stability and decomposability of its individual representatives, and, consequently, in terms of the degree of participation in the formation of the humus complex.
In addition to the various organic compounds mentioned above, we always observe in the composition of the body of dying plants and animals a different amount of the most diverse and mineral (ash) substances. All these diverse compounds, falling in the process of soil formation into various horizons of a weathered rock, undergo a different fate: some of them, becoming the property of microbes, quickly collapse and decompose, others undergo a number of complex phenomena of interaction with the mineral constituents of the soil, one of the results of which is that relatively stable and durable organomineral complex, which is called humus. These interaction phenomena are complex and diverse: there are also purely chemical reactions between the constituent parts of the weathered rock and those soluble decomposition products of organic residues that are systematically leached from the latter by atmospheric precipitation, and microbiological phenomena, consisting in diverse processes of decomposition of organic compounds and simplification their composition, and on the other hand, the reverse synthesis of products formed in the body of microorganisms in the process of their nutrition with the formation of new complex organic substances, and, finally, physicochemical phenomena associated with the colloidal state of interacting substances and leading to the formation of special "adsorption compounds" in the soil ".
Based on the fact that of all the organic compounds that make up plant residues, lignin has the greatest resistance to the decomposing action of microbes; on the other hand, stating the fact that in the process of decomposition of these residues, the accumulation of protein (and other nitrogenous) complexes occurs and, further, that in all the soils analyzed by the author, the substances mentioned now accounted for up to 80% of the total organic matter of these soils, etc. , - Waksman makes the assumption that soil humus consists of a basic and complex complex - the core, which includes fractions of mainly lignin and protein, which are in close chemical combination with each other.
This main core is accompanied by a number of other substances that either remain from the decomposition of plant and animal remains, or were synthesized due to the vital activity of microorganisms.
Among these secondary constituents of soil humus are some fats and waxes, hemicelluloses, higher alcohols, organic acids, etc. In the soils mentioned above, analyzed by Waksman, organic matter actually contains only about 16% of water-insoluble carbohydrates (cellulose, hemicellulose, etc.). ) and only 2.5-3% of substances soluble in ether and alcohol, while the amount of protein and lignin accounted for up to 80% of the total organic matter of these soils.
Taking into account that the protein fraction that enters the soil with plant and animal residues, as well as formed in it in the process of synthesizing microbial activity, can vary in its own way. chemical composition and that the lignin group can also be a complex of compounds that differ significantly from each other, it is clear that the internal constitution of the lignin-protein core in different soils, formed and developed under different conditions, can vary significantly among themselves.
Waksman was able to artificially synthesize this lignin-protein complex in a laboratory setting. The latter turned out to be, in terms of the total sum of its properties, sharply different from the properties of its individual components - lignin and protein - and at the same time acquired all those chemical, physico-chemical and biological properties that we generally consider characteristic of humus (or, more correctly, for that part of it that is called humic acid): solubility in alkalis and subsequent precipitation by acids, dark color, resistance to the decomposing action of microbes (protein substances, usually easily susceptible to the decomposing action of microorganisms, acquire, as a result of their interaction with lignin, as it turned out, greater stability).
Waksman was further able to obtain artificial compounds of the "ligno-protein" complex with various bases (Ca, Mg, Fe, Al), moreover, by methods similar to those usually used to obtain various salts of humic acid; These investigations, if further developed, can bring some clarity to the knowledge of the connection that exists between the organic core and the ash elements of soil humus. Among other things, it was found that the lignin-protein complex has
We will not drive ourselves into a strict framework from the very beginning and describe the term as simply as possible: the process of oxidation of organic substances (organics; these are, for example, proteins, fats and carbohydrates) is a reaction that results in an increase in the volume of oxygen (O2) and a decrease in the volume of hydrogen ( H2).
Organic substances are various chemical compounds that contain (C). Exceptions are carbonic acid (H2CO3), carbides (eg carborundum SiC, cementite Fe3C), carbonates (eg calcite CaCO3, magnesite MgCO3), oxides of carbon, cyanides (such as KCN, AgCN). Organic matter reacts with the best known oxidant, oxygen O2, to form water H2O and carbon dioxide CO2.
The process of oxidation of organic substances
If we think logically, then since the process of complete oxidation is combustion, then the process of incomplete oxidation is the oxidation of organic matter, because with such an impact, the substance does not ignite, but only heats it (accompanied by the release of a certain amount of energy in the form of ATP - adenosine triphosphate - and heat Q ).
The reaction of organic oxidation is not too intricate, so they begin to analyze it at the beginning of the chemistry course, and students quickly assimilate the information, if, of course, they make at least some effort. We have already learned what this process is, and now we have to delve into the very essence of the matter. So, how does the reaction proceed and what is it?
Oxidation of organic matter is a kind of transition, the transformation of one class of compounds into another. For example, the whole process begins with the oxidation of a saturated hydrocarbon and its transformation into an unsaturated one, then the resulting substance is oxidized to form alcohol; alcohol, in turn, forms aldehyde, carboxylic acid "flows" from aldehyde. As a result of the whole procedure, we get carbon dioxide (when writing the equation, do not forget to put the corresponding arrow) and water.
This is a redox reaction, and in most cases, organic matter exhibits reducing properties, and oxidizes itself. Each element involved has its own classification - it is either a reducing agent or an oxidizing agent, and we give a name based on the result of the OVR.
The ability of organic substances to oxidize
We now know that an oxidizing agent, which takes electrons and has a negative charge, and a reducing agent, which donates electrons and has a positive charge, take part in the process of ORR (oxidation-reduction reaction). However, not every substance can enter into the process that we are considering. To make it easier to understand, let's look at the points.
Compounds are not oxidized:
- Alkanes - differently called paraffins or saturated hydrocarbons (for example, methane, which has the formula CH4);
- Arenes are aromatic organic compounds. Among them, benzene is not oxidized (in theory, this reaction can be carried out, but after several long steps; benzene cannot be oxidized on its own);
- Tertiary alcohols are alcohols in which the hydroxo group OH is bonded to a tertiary carbon atom;
- Phenol is another name for carbolic acid and is written in chemistry as C6H5OH.
Examples of organic substances capable of oxidation:
- Alkenes;
- Alkynes (as a result, we will follow the formation of an aldehyde, carboxylic acid or ketone);
- Alkadienes (either polyhydric alcohols or acids are formed);
- Cycloalkanes (in the presence of a catalyst, a dicarboxylic acid is formed);
- Arenes (any substances that have a structure similar to benzene, that is, its homologues, can be oxidized to benzoic acid);
- Primary, secondary alcohols;
- Aldehydes (have the ability to oxidize then carbons);
- Amines (during oxidation, one or more compounds with the nitro group NO2 are formed).
Oxidation of organic substances in the cell of plant, animal and human organisms
This is the most important question not only for those people who are interested in chemistry. Everyone should have this kind of knowledge in order to form a correct idea about various processes in nature, about the value of any substances in the world, and even about oneself - a person.
From the school biology courses, you probably already know that the oxidation of organic matter plays an important role. biological role in the human body. As a result of redox reactions, the splitting of BJU (proteins, fats, carbohydrates) occurs: heat, ATP and other energy carriers are released in the cells, and our body is always provided with a sufficient supply to perform actions and normal functioning of organ systems.
The flow of this process helps to maintain a constant body temperature in the body of not only a person, but also any other warm-blooded animal, and also helps to regulate the constancy of the internal environment (this is called homeostasis), metabolism, ensures the quality work of cell organelles, organs, and also performs many more necessary functions.
During photosynthesis, plants absorb harmful carbon dioxide and produce oxygen, which is necessary for respiration.
The biological oxidation of organic substances can proceed exclusively with the use of various electron carriers and enzymes (without them, this process would take an incredibly long time).
The role of organic oxidation in industry
If we talk about the role of organic oxidation in industry, then this phenomenon is used in the synthesis, in the work of acetic acid bacteria (with incomplete organic oxidation, they form a number of new substances), and in some cases, with organics, the production of explosive substances is also possible.
Principles of writing equations in organic chemistry
In chemistry, one cannot do without drawing up an equation - this is a kind of language of this science, which all scientists of the planet, regardless of nationality, can speak and understand each other.
However, the greatest difficulties are caused by the compilation of equations when the study of organic chemistry is to be.
To disassemble this topic, a very long period of time is required, therefore, only a brief algorithm of actions for solving a chain of equations with some explanations has been selected here:
- First, we immediately look at how many reactions take place in this process, we number them. We also determine the classes, the names of the initial substances and the substances that are eventually formed;
- Secondly, it is necessary to write out all the equations one by one and find out the type of their reactions (compound, decomposition, exchange, substitution) and conditions.
- After that, you can draw up electronic balances, and also do not forget to set the coefficients.
Oxidation reactions of organic substances and their final products of formation
Benzene oxidation
Even under the most aggressive conditions, benzene is not subject to oxidation. However, benzene homologues can be oxidized under the influence of a solution of potassium permanganate in neutral environment to the formation of potassium benzoate.
If the neutral medium is changed to acidic, then benzene homologues can be oxidized by potassium permanganate or dichromate with the final formation of benzoic acid.
Formula formation of benzoic acid
Alkene oxidation
In the oxidation of alkenes with inorganic oxidizing agents, the end products are the so-called dihydric alcohols - glycogens. The reducing agents in these reactions are carbon atoms.
A good example of this is the chemical reaction of a solution of potassium permanganate in connection with a weak alkaline environment.
Aggressive oxidation conditions cause the carbon chain to break down double bond with the final products of formation in the form of two acids. Moreover, if the medium with a high content of alkali forms two salts. Also, products due to the breakdown of the carbon chain can form acid and carbon dioxide, but in conditions of a strong alkaline environment, carbonate salts act as products of the oxidative reaction.
Alkenes are capable of being oxidized when immersed in an acidic environment of potassium dichromate in a similar way as shown in the first two examples.
Alkyne oxidation
Unlike alkenes, alkynes are oxidized in a more aggressive environment. The destruction of the carbon chain occurs at the triple bond. A common property with alkenes is their reducing agents represented by carbon atoms.
The output reaction products are carbon dioxide and acids. Placed potassium permanganate in an acidic environment will be an oxidizing agent.
The oxidation products of acetylene, when immersed in a neutral medium with potassium permanganate, is potassium oxalate.
When a neutral medium is changed to an acidic one, the oxidation reaction proceeds to the formation of carbon dioxide or oxalic acid.
Oxidation of aldehydes
Aldehydes are easily oxidized due to their properties as strong reducing agents. As oxidizing agents for aldehydes, potassium permanganate with potassium dichromate can be distinguished, as in the previous versions, as well as a solution of silver hydroxide diamine - OH and copper hydroxide - Cu (OH) 2, predominantly characteristic of aldehydes. An important condition for the occurrence of the oxidation reaction of aldehydes is the effect of temperature.
In the video you can see how the presence of aldehydes is determined in the reaction with copper hydroxide.
Aldehydes are capable of being oxidized to carboxylic acids under the influence of silver hydroxide diamine in the form of a solution with the release of ammonium salts. This reaction is called the "silver mirror".
Further, the video demonstrates an interesting reaction, which is called the “silver mirror”. This experience takes place in the interaction of glucose, which is also an aldehyde, with a solution of silver ammonia.
Alcohol oxidation
The oxidation product of alcohols depends on the type of carbon atom to which the OH group of the alcohol is attached. If the group is linked by a primary carbon atom, then the oxidation product will be aldehydes. If the OH group of an alcohol is bonded to a secondary carbon atom, then the oxidation product is ketones.
Aldehydes, in turn, formed during the oxidation of alcohols, can then be oxidized to form acids. This is achieved by oxidizing primary alcohols with potassium dichromate in an acid medium during the boiling of the aldehyde, which, in turn, do not have time to oxidize during evaporation.
Under the condition of the excessive presence of oxidizing agents such as potassium permanganate (KMnO4) and potassium dichromate (K2Cr2O7), under almost any conditions, primary alcohols can be oxidized with the release of carboxylic acids, and ketones, in turn, into secondary alcohols, examples of reactions of which with formation products will be considered below.
Ethylene glycol or the so-called dihydric alcohol, depending on the medium, can be oxidized to products such as oxalic acid or potassium oxalate. If ethylene glycol is in a solution of potassium permanganate with the addition of acid, oxalic acid is formed, if dihydric alcohol is in the same solution of potassium permanganate or potassium dichromate, but in a neutral medium, then potassium oxalate is formed. Let's take a look at these reactions.
We found out everything that needs to be understood at first and even began to analyze such a difficult topic as solving and compiling equations. In conclusion, we can only say that balanced practice and frequent studies will help to quickly consolidate the material covered and learn how to solve problems.
Primary production on Earth is created in the cells of green plants under the influence of solar energy, as well as by some bacteria due to chemical reactions.
Photosynthesis is the process of formation of organic substances from carbon dioxide and water in the light with the participation of photosynthetic pigments (chlorophyll in plants, bacteriochlorophyll and bacteriorhodopsin in bacteria).
Assimilated photon energy is converted into bond energy chemical substances synthesized during these processes.
The basic reaction of photosynthesis can be written as follows:
where H 2 X - "donor" of electrons; H is hydrogen; X - oxygen, sulfur or other reducing agents (for example, sulfobacteria use H 2 S as a reducing agent, while other types of bacteria use an organic substance, and most green plants that carry out chlorophyll assimilation use oxygen).
Types of photosynthesis:
1. Chlorophilic photosynthesis.
2. Chlorophilic photosynthesis
a). anoxygenic photosynthesis. The process of formation of organic substances in the light, in which there is no synthesis of molecular oxygen. It is carried out by purple and green bacteria, as well as helicobacteria.
b). oxygenic photosynthesis with the release of free oxygen. Oxygenic photosynthesis is much more widespread. Carried out by plants, cyanobacteria and prochlorophytes.
The basic reaction of photosynthesis carried out by plants can be written as follows:
Stages (phases) of photosynthesis:
photophysical;
· photochemical;
chemical (or biochemical).
At the first stage, the absorption of light quanta by pigments, their transition to an excited state and the transfer of energy to other molecules of the photosystem.
At the second stage, there is a separation of charges in the reaction center, the transfer of electrons along the photosynthetic electron transport chain. There is a transition of the energy of the excited state into the energy of chemical bonds. ATP and NADPH are synthesized.
At the third stage, biochemical reactions of the synthesis of organic substances proceed using the energy accumulated at the light-dependent stage with the formation of sugars and starch. The reactions of the biochemical phase occur with the participation of enzymes and are stimulated by temperature, therefore this phase was called the thermochemical phase.
The first two stages together are called the light-dependent stage of photosynthesis - light. The third stage occurs already without the obligatory participation of light - dark.
The energy of the Sun is used in the process of photosynthesis and accumulates in the form of chemical bonds in the products of photosynthesis, and then transferred as food to all other living organisms. The photosynthetic activity of green plants provides the planet with organic matter and the solar energy accumulated in it - a source of origin and a factor in the development of life on Earth.
Among all rays sunlight usually emit rays that affect the process of photosynthesis, accelerating or slowing down its course. These rays are called physiologically active radiation(abbreviated FAR). The most active among PARs are orange-red (0.65...0.68 µm), blue-violet (0.40...0.50 µm) and near ultraviolet (0.38...0.40 µm). Yellow-green (0.50 ... 0.58 microns) rays are less absorbed and infrared rays are practically not absorbed. Only far infrared rays take part in the heat exchange of plants, having some positive effect, especially in places with low temperatures.
Synthesis of organic matter can be carried out by bacteria both with the use of sunlight and without it. It is believed that it was the photosynthesis of bacteria that was the first stage in the development of autotrophy.
Bacteria that use processes associated with the oxidation of sulfur compounds and other elements to form organic matter belong to chemosynthetics.