Hydrogen Sulfide

HYDROGEN SULFIDE, H₂S (molecular weight 34.07), a colorless gas with the characteristic odor of rotten eggs. A liter of gas under normal conditions (0°, 760 mm) weighs 1.5392 g. The boiling point is -62°, the melting point -83°. H₂S is found in the gaseous emissions of volcanoes, various sulfur springs (e.g., Pyatigorsk, Matesta), and also in the deep layers of sea water (see below), and is one of the common products of the decomposition of sulfur-containing proteins in animal organisms. Laboratory methods of preparation are based on the decomposition in a Kipp's apparatus of soluble iron or zinc sulfides by mineral acids without heating; H₂S is less frequently obtained (without hydrogen impurities) by the action of strong hydrochloric acid on antimony trisulfide Sb₂S₃ upon heating. A less common method of obtaining H₂S is by heating certain organic substances (e.g., paraffin) with sulfur. Gaseous H₂S is not very stable, however it dissociates noticeably into hydrogen and sulfur only at high temperatures (at 827° the degree of dissociation is 0.089%); H₂S burns in air, forming water and sulfur dioxide. Metals, with the exception of some noble metals (gold, platinum), in the presence of H₂S are covered with a coating of sulfides. Water vapor significantly accelerates this process. When H₂S dissolves in water (at 20°, 1 volume of water dissolves 29 volumes of H₂S, or 4.4 g in 1 liter, which corresponds to 0.13 molar or 0.26 equivalent concentration), electrolytic dissociation of H₂S into H⁺ and HS^- occurs. The degree of dissociation of hydrosulfuric acid in a 0.1 solution at 25° is 0.07%, i.e., approximately 1,400 times less than the degree of dissociation of hydrochloric acid. K = (HS) = 0.91 × 10^-3, where K is the dissociation constant; H₂S is a dibasic acid and therefore gives acid and normal salts, most of which are poorly soluble in water (with the exception of alkali and alkaline earth salts). H₂S is a very weak acid, and therefore its salts are strongly hydrolyzed in aqueous solutions. Qualitatively, H₂S is determined by the following reactions: 1) with sodium nitroprusside: in an alkaline medium, a red-violet coloration is formed (reaction for the S^2- ion); 2) by the formation of methylene blue: to the liquid being tested, add 1/50 volume of fuming HCl, a few crystals of p-amino-dimethylaniline sulfate, and after the latter has dissolved, 1-2 drops of FeCl₃ solution; after standing for 30 minutes in a closed vessel, the liquid turns blue; 3) by the formation of black lead sulfide, used in the analysis of insoluble sulfides; when they are treated with weak sulfuric acid in the presence of zinc, H₂S is released, which turns lead paper (filter paper moistened with lead acetate solution) black. Quantitative determination of H₂S is carried out by oxidimetric and iodometric methods. 1) Oxidation of H₂S by permanganate in an alkaline medium proceeds quantitatively (Kolthoff). To 25 cm³ of 0.1 permanganate solution, add 5-10 cm³ of 4% sodium hydroxide solution and 10 cm³ of 0.1 sulfide solution S^2- + 2 O₂ → SO₄^2-; after five minutes, the excess permanganate is titrated. 2) In the iodometric determination of H₂S in aqueous solutions (e.g., in mineral waters), into a liter cylinder with a measured amount of 0.01 iodine solution, 2 g of potassium iodide (KI) are added, 1,000 cm³ of the water being tested is poured in, and the excess iodine is titrated with 0.01 sodium thiosulfate solution. If H₂S content is significant, more concentrated iodine solutions or less water should be used. This method gives the total amount of S, both free and bound in the form of HS^-. In the body, small amounts of H₂S are constantly formed during the decomposition of proteins in the intestine. The introduction of significant amounts of sulfides or inhalation of H₂S is fatal to the organism. With H₂S content in the air of 0.1%, a person dies in 10 minutes; symptoms of poisoning are already noticeable with 0.02% H₂S in the air. The death of an animal from S poisoning occurs from the direct action on the central nervous system, and not from the change in the respiratory pigment of the blood, which turns into the so-called sulfhemoglobin—a greenish pigment with a characteristic spectrum. Cessation of breathing and paralysis of the vasomotor center are apparently the direct cause of death. Pulmonary edema, caused by the local irritating action of hydrogen sulfide, is also of importance. In the initial stages of poisoning, a person ceases to notice the unpleasant odor of H₂S, which increases the danger of this substance. Green spots on the corpse are due to the formation of sulfhemoglobin. When the gas is inhaled in high concentrations, the spectrum of sulfhemoglobin—two absorption bands between the C and D lines—can be detected in the blood of frogs (sometimes mammals) during life. When H₂S acts on reduced hemoglobin, sulfhemoglobin is formed, which gives only one absorption band between C and E. Sources containing small amounts of H₂S are widely used in the treatment of certain diseases (see Matesta springs, Pyatigorsk), S. Severin. Hydrogen sulfide fermentation. The biological significance of hydrogen sulfide fermentation in nature is limited to processes occurring in bodies of water. The accumulation of S in the bottom layers of water as a result of fermentation of organic-rich mud is observed in eutrophic lakes and ponds when the oxygen inflow is insufficient for the complete oxidation of S, which is usually observed in the bottom layers of sufficiently deep, organically rich lakes and in shallow lakes and ponds in winter; in the latter case, this phenomenon is accompanied by fish kills, which in some bodies of water is the main reason for their poverty in fish. In addition, hydrogen sulfide fermentation is characteristic of heavily polluted waters of polysaprobic and α-mesosaprobic types. In all these cases, a characteristic composition of the biological population is observed: in the zooplankton, almost exclusively protozoa, mainly colorless flagellates and infusoria, which can reach significant quantitative development; in the phytoplankton, blue-green oscillators and sulfur bacteria. A striking example of the influence of hydrogen sulfide fermentation on the fauna is the Black Sea, where, as a result of circulation conditions, starting from a depth of 200 m, the water contains S, which leaves a sharp imprint on the entire composition of the Black Sea fauna. Since the presence of S is always accompanied by the absence of oxygen, based on observations in nature, it is impossible to determine which of these two factors has the predominant importance in establishing the characteristic biological picture of the population of waters with hydrogen sulfide fermentation. G. Vinberg. Works in which S may be released into the air as a by-product are very numerous: in laboratories in various branches of the chemical industry, in artificial silk factories (mainly the spinning shop), in textile factories (preparation and use of sulfur dyes), in the production of ultramarine, in leather and beet sugar factories, at sulfur mineral springs, in sewer networks, cesspools, in caissons on swampy ground; sometimes it can break through in significant quantities with underground gases on oil fields. Of the industries causing the most poisonings, first place is taken by the leather and artificial silk industries. In the USSR, according to data for 1924-29, 242 cases of S poisoning were recorded, distributed by years as follows: 20, 95, 43, 82, 2 (for the last year the data is incomplete). The content of S in the air of working rooms of various industries and enterprises varies within very wide limits—from thousandths to tenths of mg/liter of air. For example, at the Odessa leather factory, amounts in the range of 0.002-0.04 mg/liter were found, at the 'Truzhenik' factory much more—0.05-0.107 mg/liter; the largest amounts were found near the vats. Many authors have studied the determination of toxic doses of S. In Rodenacker's experiments on animals, at concentrations of 1.5-10 per 1,000 of air by volume, death occurred very quickly; in Haggard's experiments, it was established that poisoning symptoms begin at doses of 0.14-0.21 mg/liter (100-159 parts per million by volume). In experiments on humans by Lehmann, symptoms of irritation of the mucous membranes, tearing with pain in the eyes, and other signs of poisoning began at approximately the same concentrations as Haggard established for dogs. The maximum permissible concentration of H₂S in the air of working rooms was established by the NKT USSR as 0.015 mg/liter of air. S has both local and general effects. The local effect is manifested as irritation of the conjunctiva, nasal mucosa, pharynx, and respiratory tract; it is accompanied by a burning sensation, tearing, photophobia, cough, and hoarseness.

With frequent and prolonged exposure, chronic conjunctivitis, inflammation, erosions and opacities of the cornea, rhinitis, laryngitis, and bronchitis develop. Many German authors report data on corneal lesions in workers in the production of artificial silk; according to Rodenacker's data, at concentrations of 0.037-0.0055 mg/l, these lesions were no longer observed in workers, but when working at washing baths, H₂S is released in very large quantities-0.15 mg/l, and eye diseases occur very frequently among the spinners working here. These data coincide with the results of a study of workers at the "Viscose" factory: in 1926, out of 96 spinners, conjunctival lesions were found in 16; in the winding department, where H₂S was detected in the air at 0.01 mg/l, no eye diseases were found. According to Dr. Kaplan, the number of eye disease cases among workers at the "Viscose" factory is still quite large- in the 3 summer months of 1932, there were 441 cases of disease per 100 workers, while at the Klin and Leningrad factories, where working conditions are much better, the number of eye diseases for the same months per 100 workers is 33 and 9, respectively. The general action of H₂S, rather than the local action, is of much greater importance, which manifests itself at significant concentrations. The picture of acute poisoning-see Poisoning. In persons subjected to prolonged exposure to low concentrations of H₂S, along with the described irritation phenomena, symptoms of chronic poisoning are observed: anemia, weight loss, irritability, headaches, dyspepsia, etc. The general action of H₂S is due to the fact that it suppresses and paralyzes cellular respiration. Rodenaker believes that the cause of the latter is the inactivation of catalytic cellular iron, and at high concentrations-also of cysteine-glutamic acid, which play a major role in cellular respiration. This causes intratissue suffocation, which leads to the rapid development of symptoms of acute poisoning. According to Volynsky, paralysis of respiratory functions also manifests itself from the side of Hb: in experiments with chronic poisoning, the ability of Hb to absorb oxygen fell to 80-85%, with acute poisoning-to 15%. In autopsies of those who died from H₂S poisoning, liquid blood is found, which takes on a gray-green color during the postmortem formation of sulfhemoglobin. Prevention. In the production of artificial silk, ventilation of work premises is of primary importance, mainly the spinning department; instead of the sulfite spinning method, which is accompanied by the release of large amounts of H₂S, it will probably be possible to introduce the nitrite method, in which the release of H₂S is negligible. In the production of sulfur dyes, the hermetization of production equipment and the mechanization of the transfer of raw materials and solutions with the absorption of the released H₂S by scrubbers, etc., can be noted, which gave a positive effect on Moscow factories. Treatment-see Poisoning. N. Rosenbaum. Discovery in forensic cases and determination in professional poisonings. Chemical discovery of H₂S in internal organs is usually not carried out, since H₂S is naturally formed in corpses during the decomposition of protein bodies. In exceptionally fresh cases, the absence of ammonia (a companion of H₂S during protein putrefaction-see Ammonium, discovery) in the presence of a large amount of H₂S, however, indicates the introduction of H₂S into the body. To determine H₂S in internal organs, they are placed in a flask, the opening of which is plugged with a cork to the lower surface of which two strips of paper are attached: one moistened with an alkaline solution of lead acetate, the other-red litmus paper for the detection of ammonia, indicating putrefaction has already occurred and thus the postmortem formation of H₂S. To detect H₂S in the air, strips of paper moistened with an alkaline solution of lead acetate can be used, along with the characteristic odor of H₂S and the blackening of copper objects. Rapid or slow blackening of "lead" paper makes it possible to judge the larger or smaller amounts of H₂S in the air. For quantitative determination, a certain volume of air is passed through absorbers with a solution of lead acetate (containing gelatin as a "protective colloid"). The dark color is compared with standard solutions. In some cases, absorption with a caustic soda solution followed by titration of H₂S with an iodine solution is possible: acetic acid is added to the alkaline liquid until an acidic reaction occurs, the excess of standardized iodine solution is added, then the excess iodine is titrated with a solution of hyposulfite. Indicator-starch. A. Stepanov.