Oxidation of inorganic sulfur compounds. Oxidation of organic matter - the basis of life
Oxidation-reduction reactions involving organic substances, their varieties, the definition of products
All IAD in organics can be divided into 3 groups:
Complete oxidation and burning
Mild oxidation
Destructive oxidation
1. Complete oxidation and burning. Oxygen (other substances that support combustion, such as nitrogen oxides), concentrated nitric acid and sulfuric acid can be used as oxidizers, solid salts can be used, when heated, oxygen is liberated (chlorates, nitrates, permanganates, etc.), other oxidizing agents (for example , copper (II) oxide). In these reactions, the destruction of all chemical bonds in organic matter is observed. Products of oxidation of organic matter are carbon dioxide and water.
2. Mild oxidationIn this case, the carbon chain does not break. Mild oxidation includes the oxidation of alcohols to aldehydes and ketones, the oxidation of aldehydes to carboxylic acids, the oxidation of alkenes to dihydric alcohols (Wagner reaction), the oxidation of acetylene to potassium oxalate, toluene to benzoic acid, etc. In these cases, diluted solutions of potassium permanganate, potassium dichromate, nitric acid, ammonia solution of silver oxide, copper (II) oxide, copper (II) hydroxide are used as oxidizing agents.
3. Destructive oxidation. Occurs in more severe conditions than mild oxidation, accompanied by the rupture of some carbon-carbon bonds. As oxidizing agents, more concentrated solutions of potassium permanganate and potassium dichromate are used when heated. The medium of these reactions may be acidic, neutral and alkaline. The reaction products will depend on this.
Destruction (carbon chain break)occurs in alkenes and alkynes - on a multiple bond, in benzene derivatives - between the first and second carbon atoms, if you count from a ring, in tertiary alcohols - in an atom containing a hydroxyl group, in ketones - in an atom with a carbonyl group.
If with destructiona fragment containing 1 carbon atom has come off, then it is oxidized to carbon dioxide (in an acidic medium), bicarbonate and (or) carbonate (in a neutral medium), carbonate (in an alkaline medium). All longer fragments are converted into acids (in an acidic medium) and salts of these acids (in a neutral and alkaline medium). In some cases, it is not the acids that are obtained, but ketones (during the oxidation of tertiary alcohols, branched radicals in the homologues of benzene, in ketones, in alkenes).
The following diagrams present possible options for the oxidation of benzene derivatives in an acidic and alkaline environment. Different colors highlighted carbon atoms involved in the redox process. Highlighting allows you to trace the "fate" of each carbon atom.
Oxidation of benzene derivatives in an acidic environment
Oxidation - is the process of electron recoil by an atom, molecule or ion, accompanied by an increase in the degree of oxidation. But, following this definition, very many organic reactions can be attributed to oxidation reactions, for example:
dehydrogenation of aliphatic compounds leading to the formation of carbon-carbon double bonds:
(the degree of oxidation of the carbon atom from which the hydrogen goes, varies from -2 to -1),
alkane substitution reactions:
(the oxidation state of a carbon atom changes from -4 to -3),
coupling reactions of halogens to a multiple bond:
(the degree of oxidation of the carbon atom changes from -1 to 0) and many other reactions.
Although formally these reactions are related to oxidation reactions, in organic chemistry, however, traditionally oxidation is defined as the process by which, as a result of the transformation of a functional group, a compound passes from one category to a higher one:
alkene ®alcohol ® aldehyde (ketone) ® carboxylic acid.
Most oxidation reactions involve the introduction of an oxygen atom into a molecule or the formation of a double bond with an existing oxygen atom due to the loss of hydrogen atoms.
And what kind of compounds are able to give oxygen to organic substances?
Oxidizing agents
For the oxidation of organic substances, compounds of transition metals, oxygen, ozone, peroxides and compounds of sulfur, selenium, iodine, nitrogen and others are usually used.
Of the oxidizing agents based on transition metals, chromium (VI) and manganese (VII), (VI) and (IV) compounds are preferably used.
The most common compounds of chromium (VI) are a solution of potassium bichromate K 2 Cr 2 O 7 in sulfuric acid, a solution of chromium trioxide CrO 3 in dilute sulfuric acid ( johnson's reagent), a complex of chromium trioxide with pyridine and reagent Saretta - CrO 3 complex with pyridine and HCl (pyridinium chlorochromate).
When organic matter is oxidized, chromium (VI) in any medium is reduced to chromium (III), however, oxidation in an alkaline medium in organic chemistry does not find practical application.
Potassium permanganate KMnO 4 in different environments exhibits different oxidative properties, while the strength of the oxidizer increases in an acidic environment:
Potassium manganate K 2 MnO 4 and manganese (IV) oxide MnO 2 show oxidizing properties only in an acidic environment.
Copper (II) hydroxide is commonly used to oxidize aldehydes. The reaction is carried out with heating, at the same time the blue hydroxide of copper (II) turns first into copper hydroxide (I) of yellow color, which then decomposes to red copper oxide (I). An ammonia solution of silver hydroxide is also used as an oxidizing agent for aldehydes ( silver mirror reaction)
I. Determination of the degree of oxidation in organic substances.
Algebraic method
In organic substances it is possible to determine the degree of oxidation of elements. algebraic method, it turns out average oxidation rate. This method is most applicable if all the carbon atoms of the organic substance at the end of the reaction have acquired the same degree of oxidation (combustion reaction or complete oxidation)
Consider:
Example 1. Charring sucrose sulfuric acid concentrate with further oxidation:
C 12 H 22 O 11 + H 2 SO 4 ®CO 2 + H 2 O + SO 2
Find the degree of oxidation of carbon in sucrose: 0
In the electronic balance take into account all 12 carbon atoms:
12C 0 - 48 e ® 12C +4 48 1
Oxidation
S +6 + 2 e ®S +4 2 24
recovery
C 12 H 22 O 11 + 24 H 2 SO 4 ® 12CO 2 + 35H 2 O + 24 SO 2
In most cases, not all atoms of organic matter undergo oxidation, but only some. In this case, only atoms that change the degree of oxidation are introduced into the electron balance, and, therefore, it is necessary to know the degree of oxidation of each atom.
2.graphically:
1) the full structural formula of the substance is depicted;
2) for each bond, the arrow indicates the displacement of the electron to the most electronegative element;
3) all C – C bonds are considered non-polar;
The carboxyl group carbon shifts 3 electrons from itself, its oxidation state is +3, the methyl carbon attracts 3 electrons from hydrogen, and its oxidation state is 3.
The carbon of the aldehyde group gives 2 electrons (+2) and attracts 1 electron to itself (- 1), for a total degree of carbon oxidation of the aldehyde group +1. The carbon of the radical attracts 2 electrons from hydrogen (-2) and gives 1 electron to chlorine (+1), for a total oxidation state of this carbon -1.
N С С С ≡ С Н
Task 1. Determine the average degree of oxidation of carbon atoms by the algebraic method and the degree of oxidation of each carbon atom by the graphical method in the following compounds:
1) 2-aminopropane 2) glycerin 3) 1,2 - dichloropropane 4) alanine
Methyl phenyl ketone
This process is carried out mainly by three groups of microorganisms: photosynthetic bacteria (purple and green), sulfur bacteria themselves, thionic bacteria.
Relatively recently discovered that some heterotrophic bacteria you. mesentericus, you. subtilis, actinomycetes, fungi and yeast are also capable of oxidizing sulfur in the presence of organic matter, but this side process is slow, and the energy released during oxidation is not used by them.
Photosynthetic bacteria - purple and green prokaryotic microorganisms, live mainly in water bodies and carry out "anaerobic photosynthesis" without the release of molecular oxygen. All phototrophic bacteria in the Bergie determinant are combined into the Rhodospirillales order on the basis of their ability to anaerobic photosynthesis; there are two suborders: Rhodospirillineae - purple (rodobacterium), Chlorobiineae - chlorobacterium (green bacteria). Most photosynthesizing bacteria are strict anaerobes and phototrophs, although among purple and green bacteria there are species that can grow heterotrophically in the dark due to respiration. As a hydrogen donor during photosynthesis, bacteria use reduced sulfur compounds, molecular hydrogen, and some species - organic compounds.
The most well-studied from the order of the rhodobacterium family Chromatiaceae, genus Chromatium - sulfur purple bacteria. Representatives of the latter are oval or rod-shaped, have mobility due to the polar flagella; they are obligate anaerobic photolithotrophic organisms, oxidize hydrogen sulfide successively to S 0 and further to SO4 2-. Sometimes sulfur globules are deposited in their cells, which gradually turn into sulphates released to the outside.
Among the green sulfur bacteria, representatives of the genus Chlorobium are well studied. These are mainly rod-shaped and vibrioid forms, multiplied by division, often surrounded by mucous capsules, strict anaerobes and obligate photolithotrophs. Many of them bring the oxidation of sulfur only to the stage of free sulfur. Elemental sulfur is often deposited outside the cells, but sulfur does not accumulate in the cells themselves.
Photosynthetic bacteria are widely distributed in water bodies; usually live in an environment that contains hydrogen sulfide (ponds, sea lagoons, lakes, etc.) and maintain its high concentration. In the soil, these bacteria do not play a significant role, while in reservoirs their activity is of great importance.
Sulfur bacteria - An extensive team of colorless microorganisms, developing in the presence of hydrogen sulfide, deposits sulfur drops inside the cells. The first studies of this group of bacteria were conducted by S. N. Vinogradsky in 1887, 1888. Applying the original microculture method, which allows changing the environment and observing a living object for a long time, Vinogradsky found that sulfur deposited in Beggiatoa cells (a typical representative of sulfur bacteria) is formed from hydrogen sulfide and can be oxidized by this microorganism to sulfuric acid. At the same time, he first proposed the concept of the existence of chemosynthesis in bacteria (in particular, in filamentous ones); they can grow in the absence of organic compounds, and the process of oxidation of inorganic sulfur serves as an energy source of respiration for them. However, the presence of chemoautotrophy in most colorless sulfur bacteria is still unreasonable, as it is possible to isolate these in pure culture: although microorganisms succeed, they are not completely sure that the isolated strains have the same physiology as those observed in nature. The characteristic given to serobacteria by S. N. Vinogradsky (1888) remains practically unchanged at present.
Colorless sulfur bacteria represent a heterogeneous group with a single common feature - the ability to deposit sulfur in cells. The systematics of these organisms are developed only to the level of the genus; not all of them can be considered firmly established. GA Zavarzin (1972), by morphological features, distinguishes among them forms: filamentous, single-celled with large cells, and single-celled with smaller ones.
Filamentous bacteria belong to five genera; the most famous of them are Beggiatoa, Thiothrix and Thioploca.
The genus Beggiatoa is represented by colorless filamentous organisms that form trichomes, resembling the algal trichomes in structure, but unlike the latter, they contain inclusions of sulfur. Trichomes never attach to the substrate, have mobility due to the formed mucus and are found in sedentary waters with a low content of hydrogen sulfide, belong to microaerophiles. On the surface of the sludge in water bodies, in their places of accumulation, they form large white spots or a delicate white mesh. All species of this kind oxidize hydrogen sulfide and sulfides to elemental sulfur, which is deposited inside the cells, and in case of a lack of hydrogen sulfide or sulfide - in the external environment. The sulfur deposited inside the cells is oxidized to sulfuric acid and released. When combined with metals, sulfates are formed.
Representatives of the genus Thiothrix are very similar in structure to the sulfur bacteria of the genus Beggiatoa, but differ from the latter in that they attach themselves to the substrate with a special mucous disc, usually found in fast flowing hydrogen sulfide waters. Their threads appear black because of the large accumulation of deposited sulfur. Thiothrix gives off-white fouling on underwater objects in a mobile environment. Thioploca tufts are found in many bodies of water, in the upper layers of sludge; located vertically, they cross the oxidation and reduction horizons, continuously moving up and down as water moves to the oxygen, then to the bottom hydrogen sulfide medium. In their thick mucous capsule, covered outside with pieces of detritus, are interlaced trichomes (they can be from 1 to 20). Thioploca bacteria were isolated from calcium-rich marine sludge and freshwater fry.
Unicellular serobacteria with large cells are represented by three genera: Achromatium, Thiovulum and Macronionas: cell sizes in all species - 10-40 microns; multiply by division or constriction; the shape of the cells are oval and cylindrical. In addition to sulfur droplets, cells often contain calcium carbonate.
Unicellular forms with small cells are combined in two genera: Thiospira and Thiobacterium. Thiospira has been little studied. The genus Thiobacterium includes three species. These fixed small sticks, surrounded by mucous capsules, are capable of forming a zoogel; sulfur in the cells is not deposited in all species.
Colorless sulfur bacteria - typical aquatic microorganisms, are common in water bodies, where hydrogen sulfide is at least poorly formed. All of them are microaerophiles, very sensitive to the concentration of hydrogen sulfide: in a medium saturated with hydrogen sulfide, they die off quickly, at a concentration of less than 40 mg / l, they develop most magnificently.
Optimal conditions for them are created in non-equilibrium systems, where hydrogen sulfide accumulates slowly and there is an alkaline or close to neutral flow medium. Among the colorless sulfur bacteria there are well growing both at low temperature and at high temperature - up to 50 ° C (in thermal springs). They can withstand high salt concentrations and develop in the black mud of salt lakes, in an almost saturated salt solution. They are still the most common in fresh waters.
Mass accumulations of sulfur bacteria can be found in ponds on the surface of the sludge; therefore, the hydrogen sulfide released in the sludge oxidizes and does not poison the water mass. In the case of contamination of water mass with hydrogen sulfide, bacteria can form at one depth or another a so-called “bacterial plate” or film, above which there is no hydrogen sulfide, and below - oxygen. For example, in the Black Sea, such a film is located at a depth of 200 m and prevents the entry of hydrogen sulphide above this level. Sulfur bacteria that inhabit it on the border of the aerobic and anaerobic zones are in a chaotic, incessant motion: going down behind the hydrogen sulfide, going up behind the oxygen. They oxidize hydrogen sulfide to elemental sulfur and get the energy necessary for the synthesis of organic substances. By chemosynthetic, due to the oxidation of 25 g H 2 S / m 2, 8 g s / m 2 per year can be assimilated (Sorokin, 1970). After dying off, microbial bodies enriched with elemental sulfur are immersed in the hydrogen sulphide zone, partially reach the bottom, where with the participation of desulfurizing bacteria decompose, sulfur is restored again to hydrogen sulfide. It is assumed that in the thickness of sea water in the boundary layer (O 2 and H 2 S) the first stage of oxidation of hydrogen sulfide is carried out by chemical means (Skopindev, 1973).
Sulfur bacteria are often concentrated in large quantities in hydrogen sulfide sources.
The participation of sulfur bacteria in the sulfur cycle is probably insignificant, although their role in preventing hydrogen sulfide poisoning of water strata and the effect on the migration and deposition of metals seems to be significant.
The main role in the oxidation of sulfur is given to thionic bacteria.
Thionic bacteria - A single morphological and biochemical group of microorganisms found in soils, fresh and salt water bodies, sulfur deposits and in rocks. Thionic bacteria receive energy through the oxidation of mineral reduced sulfur compounds such as hydrogen sulfide, sulfides, sulfite, thiosulfate, tetrathionate, thiocyanate, dithionite, as well as molecular sulfur. Sulfur formed as an intermediate product is deposited outside the cells. As an electron acceptor, they use free oxygen, and some types - nitrate oxygen. According to the type of nutrition, thionic bacteria can be divided into groups: autotrophs, mixotrophs, and lithoterotrophs. Most thionic bacteria are aerobic, although facultative anaerobes are known, such as Th. denitrifisans. Depending on the habitat, they behave differently: under aerobic conditions they carry out a process with the participation of molecular oxygen, in anaerobic they switch to denitrification and reduce nitrates to molecular nitrogen. Four genera of thionic bacteria are known: Thiobacillus - rod-shaped, motile; Thiomicrospira - spiral, mobile; Thiodendron - microcolonies of oval or helically twisted cells connected by stalks or branching hyphae. Sulfolobus - lobed, with a reduced cell wall. Since bacteria of the genus Thiobacillus, which is widespread in terrestrial and aquatic ecosystems, are especially active in the sulfur cycle, they are mainly studied.
In relation to the acidity of the environment, thiobacilli are divided into two groups: those that grow in neutral or alkaline conditions (pH 6-9) and those that grow in acidic conditions (acidophilic). For thiobacillus of the 1st group, the optimum pH value is in the range of 6-9; its species are: T. thioparus, T. denitrificans, T. novellus, T. thiocyanooxidans, T. neapolitanus. They all oxidize hydrogen sulfide, sulfur and thiosulfate. Consider the most studied representatives of this group.
T. thioparus is an autotrophic bacterium isolated by Beyerink (1904), develops when the medium is neutral, mobile (has one polar flagellum), gram-negative is able to oxidize hydrogen sulfide, hydrosulfide ion, and from sulfides only calcium sulfide. The oxidation products are sulfur, polythionates (primarily tetrathionates) and sulfuric acid. It can develop as a microaerophil and is very unstable to acidity.
Thus, the accumulation of elemental sulfur can occur due to: a) the reduction of sulfates by desulfurizing bacteria; b) oxidation of hydrogen sulfide by thionic bacteria. Elemental sulfur accumulates on the muddy bottom of brackish lakes and is found on the bottom of the Caspian Sea, where it is formed due to the oxidation of hydrogen sulfide released from silt.
The formation of many sulfur deposits is associated with the oxidizing activity of thionic bacteria. Sedimentary sulfur deposits coincide geographically with the gypsum-bearing rocks of the Permian, Lower Cretaceous, Paleogene, Neogene, and are located along the boundaries of the geostructural elements, raised or submerged. Often confined to brachyanticlines with oil fields, where rocks are usually fragmented, cracked, the arches of anticlines are destroyed, which facilitates the flow of hydrogen sulfide and saturated water to the surface. Here in the oxygen environment, abundantly populated by thionic bacteria, the process of oxidation of hydrogen sulfide with the accumulation of elemental sulfur. Such are the deposits in Central Asia: Gaurdak, Shorsu, Sulfuric hillocks in Karakum.
T. thiocyanooxidans is in many ways similar to T. thioparus, but differs in that it oxidizes besides hydrogen sulfide and rhodonite. These bacteria are found (Happold, Kay, 1934) and isolated into a pure culture (Happold, Johnston, Rogers, 1954). Morphologically, T. thiocyanooxidans - sticks with one polar flagellum, autotrophic, aerobic; for them a neutral environment is favorable; the presence of organic matter at a concentration of more than 1% inhibits their development.
T. novellus is a mixotrophic organism, discovered and isolated from the soil of R. L. Starkey in 1934, gram-negative, stationary, rod-shaped, grows well on organic media, but under certain conditions it can move from a heterotrophic type of nutrition to an autotrophic one.
The denitrifying thionic bacterium is a small, indisputable bacillus, mobile, first discovered by Beierinck: (1904) under anaerobic conditions, oxidizes the environment and its inorganic compounds to sulfates, simultaneously reduces nitrates to molecular nitrogen.
In aerobic conditions, the reduction of nitrates does not occur, and the bacteria use oxygen, air, as an oxidizing agent.
The group of microorganisms developing in an acidic environment includes: T. ferrooxidans, T. intermedius, T. thiooxidans. The pH value of 2-4 is optimal for them, but they can grow at a pH of from 0.5 to 7. The first two species do not grow at pH\u003e 5: T. thiooxidans is the most acidophilic microorganism in nature, since it maintains viability at a pH of about 0 .
T. thiooxidans - flagellum bacillus, mobile, forms mucus, autotroph, was discovered when studying the decomposition of sulfur in the soil (Waxman, Ioffe, 1922). Able to oxidize, as recently established, some organic sulfur compounds. The main substrate oxidized by this organism is molecular sulfur and sometimes thiosulfate; under aerobic conditions this process goes to the stage of sulfuric acid isolation. The oxidation energy is used to absorb carbon dioxide. The ability of this type to oxidize hydrogen sulfide and other compounds has not been finally clarified, since these compounds are unstable in an acidic environment.
Thionic iron-oxidizing bacteria T. ferrooxidans is a very interesting organisms. It is described and isolated from acidic drainage mine waters (Coiner, Hinkle, 1947), a small stick with a polar flagella, mobile, does not form a spore, does not stain by Gram, reproduces by division, chemolithotroph, pH 1.7-3.5 - optimally, aerobic. It occupies a special position among thiobacteria, since the ability to autotrophic growth is caused not only by the energy obtained by the oxidation of sulfur compounds, but also by the ferrous oxide released during the oxidation to oxide. Since the ion is Fe 2+ at pH<4 в стерильной среде устойчив против окисления кислородом воздуха, то Т. ferrooxidans можно было бы отнести к железобактериям, среди которых организм занимает определенную экологическую нишу, но по таксономическим признакам он ближе к тионовым бактериям, особенно Т. thiooxidans. Источник энергии для этого организма - окисление пирита, марказита, пирротина, антимонита и других сульфидов; остальные тиобактерии обладают меньшей способностью окислять нерастворимые в воде сульфиды тяжелых металлов. Окисление Fe 2+ этим организмом - сложный, до конца не выясненный процесс. Установлено, что окисление 1 г/ат Fe 2 + до трехвалентного при pH 1,5 дает энергию - 11,3 ккал и при этом выделяется теплота - 10 ккал/моль (Медведева, 1980).
T. ferrooxidans is characterized by high resistance to heavy metal concentrations: it withstands a 5% solution of copper sulfate, a Cu concentration of 2 g / l or arsenic 1 g / l, develops with small doses of nitrogen, phosphorus and slight aeration, therefore it lives in the zone oxidation of sulfide deposits. Oxidized iron in an acidic environment does not form any formed structures, and the cells of bacteria are almost always free. Bacteria oxidize elemental sulfur, sulfides, thiosulfate, tetrathionite, hydrosulfide. In sulphide deposits it performs a double function: it oxidizes sulfur of sulphates to sulfuric acid, which in turn dissolves iron hydroxides, iron oxide sulphate is formed, the latter, reacting with sulphides, contributes (due to the reduction of iron) to chemical oxidation of bivalent sulfur, which is part of sulphides, up to hexavalent.
A number of thionic bacteria can oxidize various sulfide minerals (Cu, Zn, Pb, Ni, Co, As), participate in the change in the valence states of uranium and vanadium, withstand high concentrations of metals, develop in a solution of copper sulfate with a concentration of up to 6%. The scale of activity of these organisms is impressive. So, for one day, 6115 kg of copper and 1706 kg of zinc were removed from the Degtyarskoe deposit (Kravaiko et al., 1967). Many bacteria are found on ore minerals and receive, due to their oxidation, the energy necessary for the assimilation of carbon dioxide. Thionic bacteria, attributed to the genus T. ferrooxidans, are found in all antimony deposits. They oxidize antimonite in acidic conditions of the environment (in the presence of pyrite). Under neutral and weakly alkaline conditions, other bacteria, T. denitrificans, may accelerate the oxidation of antimonite. At the first stage, sulfur oxidation of antimonite occurs under the influence of T. ferrooxidans or other thiobacilli; antimony sulfate is unstable and hydrolyzes Sb 2; Antimony peroxide, the mineral senarmonite, is formed. Oxidation of trivalent antimony to higher oxides of Sb 5+ occurs when exposed to the autotrophic microorganism Stibiobacter senarmontii, for which the neutral environment is most favorable. Chebosynthesizing microorganism oxidizing senarmonite - Stibiobacter gen. nov .: the mineral of the group of stibiconite (Lyalikova, 1972).
Heterotrophic bacteria are widespread in ore deposits, the geochemical activity of which is still very poorly studied. However, it has been established that some of them (Pseudomonas denitrificans, P. fluorescens), isolated from sulphide ores, are oxidized. Whether they can use the oxidation energy of reduced sulfur compounds is still not clear. Obviously, their activity is associated with the formation of organic acids that can decompose minerals.
So, in the oxidation zone of sulfide deposits, a sulfate environment arises, sulfides are replaced by sulfates, weathering is acidic, minerals of ore-bearing rocks are simultaneously destroyed, they are replaced by secondary minerals - jarosite, goethite, anglesite, antlerite, digenite, etc. Over the oxidized ore body when formed in large The scale of iron oxides is formed by the so-called "iron hat". If the host rocks are carbonate, then when exposed to sulfuric acid, a large amount of gypsum is formed, sulfuric acid is neutralized. If the rocks are non-carbonate, then aggressive sulphate waters remove alkaline and alkaline-earth metals, heavy metals of the iron group and others from the aquifers in the form of sulfates; bleached zones are formed, where the most stable sulfuric acid minerals, quartz, remain, and kaolinite from secondary minerals.
At the exit to the surface in the form of sources, acidic waters, enriched with sulphates of copper, zinc, cobalt, iron, aluminum, nickel and other elements, cause the formation of acidic (thionic) solonchaks. In similar salt marshes near one of the copper-sulphide deposits of the Southern Urals, a birch grove appeared among the dry steppe.
Acid alum (thionic) soils are common on swampy sea coasts, in drying coastal Deltas, which is associated with the oxidation of hydrotroillite and pyrite, which were formed in the past due to the recovery of sulphate of sea waters with a higher water content and domination of the restoration regime. The oxidation of sulfides with thionic bacteria is accompanied by the formation of sulfuric acid, the replacement of calcium carbonates with gypsum, the dissolution of aluminum and iron oxides with the formation of alum: Al 2 (SO 4) 3, Fe 2 (SO 4) 3. Acid swamped alum soils form in temperate latitudes on the lowland coasts of Sweden and Finland (Gulf of Bothnia), on polders and marches of the Netherlands, they are not uncommon in the deltas of subtropical and tropical rivers, found in the Murray delta, in South-East Asia, South America, where have local names, for example: "poto-poto", "katclay", etc.
Sulfuric acid weathering is characteristic of the sulfur deposits emerging on the surface, around which a zone of bright white leached rocks is formed, acidic "vitriol" waters with a high content of ferrous sulfate are formed. When these waters are mixed with fresh waters, a rusty precipitate of iron oxide hydrate (limonite) precipitates, framing the zone of sulfuric acid weathering.
During the development of sulphide ores and sulphurous coals, sulphides extracted to the surface are oxidized; acidic mine waters are formed in which thionic bacteria develop. These waters are very aggressive, corroding metal equipment. Acidic waters with a pH of 1.5-2.0 flow from waste dumps, coal heaps containing scattered sulphides, vegetation dies under their influence, sharp acidification and soil degradation are observed. To localize and neutralize these flows, special calcareous barriers are laid in their path, liming of soils contaminated with acidic waters is carried out.
Sulfur Isotope Fractionation. Four stable isotopes of sulfur are distributed in the earth's crust. The ratio of sulfur isotopes in different natural objects is not the same. As a standard, the ratio S 32 and S 34 in sulphide meteorites is accepted, where it is 22.21.
There is a tendency to deplete the heavy isotope of natural sulfur compounds formed with the participation of microorganisms, these are sulfides of sedimentary origin and biogenic hydrogen sulfide; sulphides of igneous rocks and evaporite sulphates, on the contrary, are enriched relative to the standard with a light isotope of sulfur.
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Oxidation of organic matter - the basis of life
Organic matter and the energy contained in them, which is formed in the cells of any organism in the process of assimilation, undergo a reverse process - dissimilation. When dissimilation is released, chemical energy is released in the body into various forms of energy - mechanical, thermal, etc. The energy released during dissimilation is the same material basis that carries out all life processes - the synthesis of organic substances, the body’s self-regulation, growth, development , reproduction, body reactions to external influences and other manifestations of life.
Dissimilation, or oxidation, in living organisms is carried out in two ways. In most plants, animals, humans and protozoa organisms, the oxidation of organic substances occurs with the participation of atmospheric oxygen. This process is called the "breath", or aerobic (from the Latin. Aer - air) process. In some groups of plants that are able to exist without air, oxidation occurs without oxygen, that is, anaerobically, and is called fermentation. Consider each of these processes separately.
The concept of "breathing" originally meant only the inhalation and exhalation of air by the lungs. Then, the exchange of gases between the cell and its environment was called “breathing” - oxygen consumption and carbon dioxide release. Further in-depth studies have shown that breathing is a very complex multi-step process that takes place in every cell of a living organism with the obligatory participation of biological catalysts - enzymes.
Organic matter, before turning into a "fuel" that gives energy to the cell and the body as a whole, must be properly treated with enzymes. This treatment consists of the breakdown of large molecules of biopolymers — proteins, fats, polysaccharides (starch and glycogen) —in monomers. Thereby, a certain universalization of nutrient material is achieved.
Thus, instead of many hundreds of different polymers, such as food, several dozen monomers — amino acids, fatty acids, glycerol, and glucose — are formed in the intestines of animals, which are then delivered to animal and human tissue cells through the blood and lymphatic pathways. The cells are further universalizing these substances. All monomers are transformed into simpler carbon-chain carboxylic acid molecules containing from two to six atoms. If there are several dozen monomers, twenty of them are amino acids, then there are only ten carboxylic acids. So the specificity of nutrients is finally lost.
But carboxylic acids are only precursors of the material, which can be called “biological fuel”. They themselves can not yet be used in the energy processes of the cell. The next stage of universalization is the removal of hydrogen from carboxylic acids. This produces carbon dioxide (CO 2), which the body exhales. The hydrogen atom contains an electron and a proton. For the energy of the cell and the organism as a whole (bioenergy), the role of these constituent parts of the atom is far from equivalent. The energy enclosed in the atomic nucleus is not accessible to the cell. The transformation of the electron in the hydrogen atom is accompanied by the release of energy, which is used in the life processes of the cell. Therefore, the release of the electron ends the last stage of the universalization of biofuel. During this period, the specificity of organic substances, their constituents and carboxylic acids does not matter, because all of them ultimately lead to the formation of an energy carrier - an electron.
The excited electron combines with oxygen. Having received two electrons, oxygen is charged negatively, adds two protons and forms water. This is the act of cellular respiration.
Oxidation of organic substances in cells occurs in mitochondria, which, as already noted in the previous brochure, play the role of a dynamo that converts the energy of combustion of carbohydrates and fats into the energy of adenosine triphosphate (ATP).
Oxidation in the body are primarily carbohydrates. The initial and final processes of oxidation of carbohydrates can be expressed by the following formula: C 6 H 12 O 6 + 6O 2 = 6СO 2 + 6H 2 O + energy.
In animal and plant organisms, the respiration process is basically the same: its biological meaning in both cases consists in receiving energy from each cell as a result of the oxidation of organic substances. The ATP formed in this process is used as an energy accumulator. It is with this battery that the need for energy is replenished, no matter where in the cells of any organism it arises.
In the process of breathing, the plants consume oxygen in exactly the same way as animals, and release carbon dioxide. In both animals and plants, breathing is continuous day and night. Cessation of respiration, for example, by stopping the access of oxygen, inevitably leads to death, since the vital activity of cells cannot be maintained without continuous use of energy. In all animals, except microscopically small, oxygen cannot in sufficient quantities directly into the cells and tissues of the air. In these cases, gas exchange with the environment is carried out using special organs (trachea, gills and lungs). In vertebrates, the supply of oxygen to each individual cell occurs through the blood and is provided by the work of the heart and the entire circulatory system. The complexity of gas exchange in animals for a long time prevented us from finding out the true essence and significance of tissue respiration. Scientists of our century took a lot of effort to prove that oxidation takes place not in the lungs and not in the blood, but in every living cell.
In a plant organism, the mechanisms of gas exchange are much simpler than in animals. The oxygen of the air penetrates into each leaf of the plants through special openings - the stomata. Gas exchange in plants is carried out over the entire surface of the body and is associated with the movement of water through the vascular bundles.
Organisms whose oxidation occurs due to free oxygen (atmospheric or dissolved in water) are called, as already noted above, aerobic. This type of exchange is characteristic of the vast majority of plants and animals.
All living creatures on Earth in the process of breathing annually oxidize billions of tons of organic matter. At the same time a huge amount of energy is released, which is used in all manifestations of life.
French scientists L. Pasteur in the last century showed the possibility of the development of some microorganisms in an oxygen-free environment, that is, “life without air”. The oxidation of organic substances without oxygen is called fermentation, and organisms capable of active life in an environment devoid of oxygen are called anaerobic. Thus, fermentation is a form of dissimilation in the anaerobic type of exchange.
During fermentation, in contrast to respiration, organic substances are not oxidized to the final products (CO 2 and H 2 O), but intermediate compounds are formed. The energy contained in organic substances is not all released, part of it remains in the intermediate fermenting substances.
Fermentation, like breathing, is carried out through a series of complex chemical reactions. For example, the final results of alcoholic fermentation are represented by the following formula: C 6 H 12 O 6 = 2CO 2 + 2C 2 H 5 OH + 25 kcal / g mol.
As a result of alcoholic fermentation, a partial oxidation product - ethyl alcohol - is formed from sugar (glucose) and only a small part of the energy contained in carbohydrates is released.
An example of anaerobic organisms can serve as yeast fungi, which receive energy for life, assimilating carbohydrates and subjecting them to alcoholic fermentation in the process of dissimilation. Many anaerobic microorganisms break down carbohydrates to lactic, butyric, acetic acid, and other products of incomplete oxidation. Some types of bacteria can use as an energy source not only sugars, amino acids and fats, but also animal excretion products, such as urea and uric acid, contained in urine, and substances that make up the excrement. Even penicillin, which kills many bacteria, is used by one type of bacteria as a nutrient.
Thus, in the process of synthesizing organic compounds, it is as if they are “preserved” in them or stored up the energy of chemical bonds spent on their synthesis. It is released again during the reverse process of decomposition of organic substances. In terms of energy, living beings are, as already mentioned, open systems. This means that they need energy from outside in a form that allows it to be used to perform work that is inextricably linked with life manifestations, and release the same energy into the environment, but in an impaired form, for example, in the form of heat, which is dissipated in environment. Due to the continuous processes of synthesis and decay, assimilation and dissimilation in living beings, there is a constant circulation of substances and the transformation of energy. What amount of energy was absorbed, as much of it is released during dissimilation. The energy released during dissimilation carries out processes that characterize the essence of life and all its manifestations.
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