Chlorine

CHLORINE, Cl₂, a chemical element, atomic number 17, atomic weight 35.457. Located in Group VII of the third period, chlorine atoms have 7 outer electrons, due to which chlorine behaves as a typical monovalent metalloid. Chlorine is divided into isotopes with atomic weights of 35 and 37. In nature, chlorine is not found in a free state; in a combined state, it is very common, especially in the form of sodium and potassium chlorides, in rock salt deposits, in seawater, and in plant and animal organisms (in gastric juice, urine, blood, etc.). It was first obtained by Scheele in 1774 by the action of hydrochloric acid on manganese dioxide upon heating: 4HCl + MnO₂ -> 2H₂O + MnCl₂ + Cl₂, a method that is often used in laboratory practice even today, replacing HCl with table salt and concentrated sulfuric acid: MnO₂ + 2NaCl + 2H₂SO₄ -> MnSO₄ + Na₂SO₄ + 2H₂O + Cl₂ (Berthollet's method). These same reactions are also implemented in industry. To obtain chlorine in large quantities, the Deacon process is used, based on the decomposition of CuCl₂ into chlorine and CuCl upon heating. Cuprous chloride is oxidized by atmospheric oxygen into Cu₂Cl₂O, which, with hydrogen chloride, again yields CuCl₂. Recently, the electrolytic method of obtaining chlorine has developed strongly and taken first place. Electrolysis is conducted either on aqueous solutions of table salt or on molten anhydrous salt. In the first case, along with chlorine, hydrogen and caustic soda are obtained: 2NaCl -> Cl₂ + 2Na; 2Na + 2H₂O -> 2NaOH + H₂; to prevent the caustic soda released at the cathode from penetrating to the anode, where chlorine is released, the anode and cathode spaces are separated by a semi-permeable diaphragm. During the electrolysis of molten salt, along with chlorine, metallic sodium is obtained, to dissolve which the cathode is made of mercury, forming sodium amalgam, from which sodium is then extracted. The resulting chlorine is a yellowish-green gas with a characteristic suffocating odor, easily condensing into a liquid at ordinary temperatures, since its critical temperature lies very high (+144.0°); critical pressure is 76.1 atm; at 20° under a pressure of 6.6 atmospheres, chlorine condenses into an orange-yellow liquid, in which form it is used for storage and transport (in steel cylinders). Liquid chlorine boils at -34.7°. Melting point is -101.5°. Chlorine is 2.49 times heavier than air; 1 volume of water dissolves 1.74 volumes of chlorine at 0°, approx. 3 volumes at 10°, and 1.5 at 50°. The aqueous solution is called chlorine water (aqua chlorata) and is used after dilution in medical and laboratory practice. Chlorine water decomposes rapidly under the action of light with the formation of HCl and O₂, which is why it must be stored in dark, well-closed bottles. Chlorine belongs to the halogen group, reacts very energetically with hydrogen (with an explosion), with metals (even with gold and platinum; the active principle of 'aqua regia'—a mixture of concentrated HCl and HNO₃—is Cl), and with many metalloids (e.g., P burns in chlorine, yielding PCl₃ and PCl₅). Chlorine is a component of many inorganic salts, such as chlorides (NaCl, KCl, HgCl, HgCl₂, etc.), hypochlorites [NaOCl, Ca(OCl)₂], chlorates (KClO₃), and perchlorates (KClO₄), as well as numerous organic substances, such as ethyl chloride, chloroform, carbon tetrachloride CCl₄, isopral CCl₃CHOHCH₃, chloral hydrate, chloroacetone CH₂ClCOCH₃, trichloroacetic acid CCl₃COOH, phosgene, diphosgene, chloropicrin, and others. Chlorine is used for disinfection, water purification (instead of chlorinated lime), bleaching, and the production of aluminum chloride, tin, sulfur, phosphorus, chlorinated lime, chloral, and a whole range of poisonous substances. Due to its strong effect on mucous membranes and the central nervous system, chlorine is a potent poisonous substance. For symptoms of acute poisoning and treatment, see Poisoning. Detection of chlorine is possible by its color and characteristic odor. Chlorine water in a 1:2 dilution is used as a strong antiseptic agent for gargling in cases of angina, stomatitis, for trachoma (1-2 drops into the conjunctival sac), and for putrid or infected wounds and ulcers. For HCl, see Hydrochloric acid.

A. Kuzin. From a toxicological point of view, chlorine as a chemical warfare agent is classified as a choking agent with immediate manifestation of signs of poisoning. Chlorine enters the body through the respiratory organs, affecting the entire respiratory apparatus, but especially severely the upper respiratory tract. Under certain conditions, chlorine also affects the skin. Along with its local effect, chlorine also possesses a general effect. The toxicity of chlorine is lower than the toxicity of many other chemical warfare agents. Serious chlorine poisoning occurs at a concentration of 0.3 mg/l (depending on exposure). According to literature data, the c-t for chlorine is 7,500. In combat concentrations, chlorine possesses significant irritating properties. The first signs of chlorine poisoning appear immediately as soon as the affected subject has inhaled the first portions of chlorine. The injury manifests as irritation, smarting, burning, and pain in the nose, nasopharynx, larynx, and trachea, accompanied by coughing, chest pain, and respiratory distress; often, a spasm of the glottis or bronchospasm occurs early. Very quickly, the poisoned individual develops rhinitis, rhino-pharyngitis, pharyngo-laryngitis, laryngo-tracheitis, and bronchitis, ranging from a mild catarrhal form to a hemorrhagic-purulent form with hemorrhages and necrosis, both in separate limited areas and sometimes over a large extent. In serious cases of poisoning, chlorine causes rapidly developing pulmonary edema, which reaches its maximum by the 12th-15th hour, and sometimes even earlier. The fully developed clinical picture of chlorine poisoning in many respects resembles phosgene poisoning, with the only difference being that with chlorine, the upper respiratory tract is also affected. The patient's complaints usually boil down to pain and burning in the nose, nasopharynx, and chest, a painful cough with abundant frothy discharge, dyspnea, and weakness. The patient (poisoned individual) develops pulmonary edema, emphysema, anoxemia, and blood changes in the same directions as with phosgene. These changes in chlorine poisoning occur earlier and progress faster (see Phosgene). The body temperature of the poisoned individual usually rises shortly after poisoning, reaching 38-39° and remaining at this height throughout the entire acute (pulmonary-asphyxial) period, i.e., about 2 days. Subsequently, if a secondary infection joins, pulmonary-inflammatory diseases arise—bronchopneumonia, pleurisy, etc. (pulmonary-inflammatory period). In cases of fatal poisoning, with a rapid increase in symptoms and a deteriorating condition, the body temperature quickly drops to 35°, dyspnea increases, cardiac activity deteriorates sharply, and the patient dies. The critical moment in chlorine poisoning is the first to second day (maximum number of deaths). The total duration of the illness is 10-30 days (in cases of survival), depending on the severity of the poisoning, complications, and consequences. The complications here are similar to those that occur with phosgene poisoning. The mortality rate fluctuates within wide limits, depending on many causes (see Phosgene). In the war of 1914-1918, it was initially 25%, and by the end, it had decreased to 2%. Autopsy shows a similar picture to phosgene poisoning, but with greater changes in the upper respiratory tract (hyperemia, hemorrhages, necrosis of the mucosa, vasodilation, edema of the submucosa). Prophylaxis—gas mask. Measures of assistance—see Phosgene.

A. Glebovich. Chlorine as an industrial poison is encountered in a large number of industries: in the production of Chlorine itself and its compounds (mainly chlorinated lime), various organic chlorine compounds, suffocating gases, during the use of calcium hypochlorite (chlorinated lime) or sodium solutions for bleaching in the textile and pulp and paper industries, and furthermore, in chlorination processes in various industries, etc. One can get an idea of the effect on the organism of various concentrations of Chlorine in the air from the data of Lehmann and Hess: at 25 mg/l death occurs instantly, at 0.15-0.01 mg/l after 1/2-1 hour, at 0.04-0.06 mg/l upon inhalation for 1/2 hour it is dangerous to life, 0.01 mg/l is tolerated without consequences for 1/2-1 hour, 0.003-0.006 mg/l is tolerated without consequences for 6 hours. In the summary table of Henderson and Haggard, compiled from the data of a number of authors, the following figures on the toxicity of Chlorine are given: Symptoms, Chlorine concentration in mg/l: 0.01, 0.04, 0.08, 0.003, 0.012, 0.12-0.18, 2.8. The smallest amount causing [symptoms], the smallest amount causing [symptoms], maximum concentration permissible for prolonged exposure... maximum concentration permissible for short-term exposure (1/4-1 hour)... dangerous upon short-term exposure... rapid death upon short-term exposure. The maximum permissible concentration of Chlorine has been established at 0.002 mg/l. Poisoning by Chlorine in industrial conditions is usually mild in nature, and therefore the number of poisonings according to foreign data (with loss of ability to work) is comparatively small. Poisonings were especially frequent here during the filling of Chlorine into cylinders (in recent years the situation here has improved significantly). For the detection (qualitative reaction) of Chlorine in the air, the following are used: 1. Iodine-starch papers, which turn blue in the presence of Chlorine. 2. The fluorescein reaction (Babini reaction). For the quantitative determination of Chlorine in the air, the simplest method is drawing the test air through a solution of potassium iodide with subsequent titration with hyposulfite in the presence of starch. With prolonged exposure to small concentrations, chronic catarrhs of the upper respiratory tract, conjunctivitis, and bronchitis develop; on the basis of these processes, the development of secondary infectious lesions is possible. Phenomena of dyspepsia, anemia, dizziness, headaches, etc., are not rare; the development of cachexia, premature aging, destruction of teeth, etc., is also noted. The effect of Chlorine on mucous membranes is explained by the fact that upon contact with them, Chlorine dissolves and turns into hydrochloric acid, however, the latter possesses a much weaker (by 20 times) irritating effect than Chlorine. According to Henderson and Haggard, Chlorine acts on tissues in the same way as on other moist organic substances—it removes hydrogen from water, thereby releasing O₂, acting in statu nascendi, and simultaneously forming hydrochloric acid; consequently, the primary effect is that of O₂. Upon inhalation, Chlorine also enters the blood, which explains the general phenomena observed during acute poisoning: increased pulse, dilation of the heart, cardiac weakness, leukocytosis, a shift of the leukocyte formula to the left, and other phenomena. In those working in the production of Chlorine via electrolysis, skin lesions in the form of acne are often observed. The latter, besides scars and pigmentation, can sometimes cause general exhaustion and in rare cases chronic septicemia. In the opinion of a number of authors, chlorine acne is caused not by the chlorine itself, but by organic aromatic chlorine compounds formed at the anode. Prophylaxis. The main attention should be directed to the soda industry, which yields the greatest number of poisonings; here, an increase in the absorption capacity of the cells, the establishment of careful supervision of the equipment, the installation of supply and exhaust ventilation, etc., are necessary. Thanks to the implementation of these measures, the number of poisonings has significantly decreased. In the textile industry, conditions during the preparation of bleaching solutions have improved thanks to the transition to working with liquid Chlorine; during the bleaching process, covering of the fittings, supply and exhaust ventilation, and other measures are necessary. Treatment. In case of poisoning—immediate removal from the poisoned atmosphere, rest, inhalation of oxygen, stimulants, etc.; upon the cessation of acute phenomena—prolonged rest.

N. Rosenbaum. The use of Chlorine in disinfection. In terms of the degree of disinfecting action, Chlorine occupies one of the first places among disinfectants; it possesses not only bactericidal but also a very energetically expressed sporicidal action (according to Geppert, a 0.2% solution of Chlorine destroys anthrax spores within 15 seconds). In the mechanism of the disinfecting action, Chlorine possibly plays not a direct, but only an intermediary role. According to the majority of authors, the disinfecting property belongs not to Chlorine, but to O₂, which forms in statu nascendi during the interaction of Chlorine with water: Cl₂+H₂O=HCl+HClO; the latter compound (hypochlorous acid) is not stable, it quickly decomposes into HCl and O (in statu nascendi). It must be noted, however, that the decomposition of water by Chlorine occurs only to a very insignificant degree. According to some authors, not only O₂, but also the Cl-ion still plays an active role in disinfection. Chlorine is used both in a gaseous state and in the form of chlorine-containing products—chlorine water, chlorinated lime, antiformin, and chloramine. Gaseous Chlorine, used in the form of fumigation, in a moist environment exhibits bactericidal and even sporicidal action; in this same form of application, Chlorine acts also as a disinsecting agent, destroying, for example, lice in the timeframes usual for disinsecting gases—12-24 hours. However, Chlorine fumigations are rarely used due to the ability inherent in this gas to distribute unevenly in the air environment, and especially due to the damage to many objects of disinfection under the influence of the effect of Chlorine on them. Chlorine water with a content of 4-5‰ of gas can be obtained by saturating water in a glass vessel from a cylinder with liquefied Chlorine until the formation of an intensely green liquid (saturation limit). Chlorine water is successfully used for disinfection, especially regarding anthrax, by washing contaminated surfaces of floors, walls, etc., in premises for the storage, sorting, and processing of raw materials of animal origin (hides, wool, horsehair, bristles, etc.); for the same purpose, chlorine water is used for the disinfection of premises for animals (in military-veterinary affairs on the basis of the circular of the People's Commissariat for Military and Naval Affairs dated 15/VIII 1929 No. 51), as well as for the disinfection of wagons for the transport of livestock and similar purposes. In all these cases, one has to reckon with the inevitable damage to metal equipment, therefore the use of chlorine water is limited here as well to strictly defined indications. Chlorinated lime, CaCl₂ + Ca(OCl)₂ + Ca(OH)₂ + 2H₂O, besides the disinfection of drinking water and sewage liquids (see Sewage waters, disinfection of sewage waters), is used for the neutralization of excreta and discharges of patients with intestinal infections, the contents of sewage receptacles and refuse, and similar purposes. Due to the energetic chlorine absorption by organic substances, significant doses of chlorinated lime and long exposure times are required for the disinfection of rotting refuse; for example, the Eberth bacillus is more reliably destroyed in homogeneous masses of feces on the condition of using 2.5 g of active Chlorine per 1 liter or 1 kg of the object of disinfection, i.e., 1% chlorinated lime with thorough mixing of the interacting masses and a 24-hour period of their contact. The disinfection of the entire contents of sewage receptacles and refuse represents an almost unsolvable task, therefore it is more expedient to disinfect the excreta of infectious patients at their bedside as part of current disinfection in such a way that infected material does not enter the receptacles; if this requirement is observed, one can limit oneself only to the surface pouring of refuse receptacles with 10% or 20% chlorinated lime milk (the latter is the usual form of using chlorinated lime). Chlorinated lime finds wide application for the purpose of de-yperiting people and all kinds of objects contaminated with yperite (soil, water, premises, furnishings, etc.). A solution of chlorinated lime is obtained by mixing the product with water in an amount of 1-10%; after thorough mixing and decantation, the settled transparent liquid is poured off and used in the same cases as chlorine water. Chlorine is the active principle of antiformin (see) and chloramine (see) used for disinfection.

G. Chistyakov. Detection in forensic chemical cases and in occupational poisonings. Chlorine, under the influence of water, quickly converts into hydrochloric and hypochlorous acids according to the equation: Cl₂ + H₂O -> HCl + HClO; hypochlorous acid, by oxidizing organic substances, in turn is reduced to HCl: HClO -> O + HCl. Thus, chlorine converts into chlorine ions, a constituent part of the organism, which makes the detection of free chlorine during poisoning by it almost impossible. For attempts to detect chlorine or hypochlorous acid, the object of investigation (viscera, etc.) is placed in a distillation flask and, with a current of carbon dioxide, chlorine and hypochlorous acid are displaced into a solution of sulfur dioxide; after the removal of the latter by boiling, the chlorine ion is detected with silver nitrate. To detect chlorine in the air, papers moistened with a solution of potassium iodide and starch paste are used: the displacement of iodine by chlorine causes them to turn blue. The reaction is not specific and has only negative value, as the release of iodine can be caused by other oxidizers (e.g., nitrogen oxides). A specific reaction is the turning pink of papers moistened with a solution of fluorescein containing an excess of potassium bromide, a little potassium carbonate, and glycerin (formation of eosin). For the quantitative determination of chlorine in the air, the latter is drawn (see Poisons, isolation) through a solution of potassium iodide and the released iodine is titrated with hyposulfite. For the determination of small quantities of chlorine in the air, colorimetric determination is used: the turning pink (oxidation) of a solution of dimethyl-p-phenylenediamine. This method requires precautions in view of analogous reactions with other oxidizers. A. Stepanov. Lit.: Anichkov S., Lastochkin P., Leonardov B. and Likhachev A., Healthcare in Conditions of Chemical Defense, Moscow-Leningrad, 1931; Vainshtein G., On the Question of Chlorine Poisoning, Ozd. truda i revolyuts. byta, issue 6, Moscow, 1929; Glebovich A., Grigoryev A. and Drugov Yu., Short Course on Military Chemical Affairs, Moscow-Leningrad, 1933; Vnyuko V., Chlorine Plant and Its Installation, Moscow-Leningrad, 1932; Zhitkova A., Methodology for Determining Harmful Gases and Vapors in the Air, Leningrad, 1934; Kalf-Kalif, Materials on the Question of the Influence of Gaseous Chlorine on the Organism of Workers in the Chemical Industry, Trudy Ukr. in-ta rab. med., issue 5, Kharkov, 1926; Krichevsky I., Pathogenesis of the Toxic Action of Gaseous Chlorine, Zhurn. mikrobiol., patol. i inf. b-ney, vol. III, issue 2, 1926; Kucherov M., Table Salt and Its Technical Use, Leningrad, 1933; Lazarev N., On the Strength of the Narcotic Action of Vapors of Chlorine-Substituted Derivatives of Methane, Ethane and Ethylene, Zhurn. eksp. biol. i med., 1929, No. 33; Lazarev and Astrakhantsev, Chemically Harmful Substances in Industry, part 1, Moscow-Leningrad, 1933; Liberman, Chemistry and Technology of Poisonous Substances, Moscow-Leningrad, 1931; Lindeman, Toxicology of Chemical Warfare Agents, Moscow, 1928; Litkes V., Experience of Experimental Study of the Influence on the Organism of Work in an Atmosphere of Harmful Vapors and Gases, Gig. truda, 1925, No. 12; Industrial Poisons, collection edited by N. Rosenbaum, Moscow-Leningrad, 1933; Sass-Tisovsky B., Production of Chlorine, Leningrad, 1933; Khomyakov V., Short Course on Chlorine Technology, Moscow-Leningrad, 1933; Flury F. and Zernik F., Schädliche Gase, Dämpfe u. s. w., Berlin, 1930; Hygiene du travail, v. I, pp. 539-546, Geneve, 1930; Martin E., L'intoxication par le chlore, Med. du travail, 1932, No. 3-4; Wenze H., Zellstofferzeugung mit Hilfe von Chlor, Berlin, 1927.