Chlorinated Hydrocarbons

CHLORINATED HYDROCARBONS. From the vast group of organic substances used in industry as solvents, one should distinguish a large group of chlorinated hydrocarbons—substances which, due to their special technical properties (good dissolving capacity combined with non-inflammability and non-combustibility), have found extensive application in the USA and Western European countries in a very large number of industries: machine building, aviation, automotive, electroplating, footwear, artificial leather, canning, oil extraction, and many others; they are further used for cleaning clothes and linens, for hair washing, for disinfection and disinsection, for filling fire extinguishers, for refrigeration, and others. Use is found for chloro-derivatives of methane (methyl chloride, dichloromethane, chloroform, carbon tetrachloride), acetylene (ethylene chloride, dichloroethylene, trichloroethylene, perchloroethylene, tetrachloroethane, pentachloroethane), aromatic hydrocarbons (mono- and dichlorobenzene), and many others. In the USSR, chlorinated hydrocarbons are currently used only on a small scale, but in the coming years, a number of these substances will be introduced into industry. Chlorinated hydrocarbons require special attention due to their toxic properties; many of them represent serious and dangerous industrial poisons, work with which requires the observance of special precautionary measures. Compared to the parent hydrocarbons, they possess a much sharper effect on the organism; this effect manifests itself in the irritation of mucous membranes and in damage to the central nervous system; in the clinical picture of poisoning, phenomena of narcosis come to the fore, alternating with symptoms of excitation; furthermore, chlorinated hydrocarbons have a strong effect on parenchymatous organs (heart, liver, pancreas, etc.; chloroform, carbon tetrachloride, and tetrachloroethane act particularly sharply on the liver). Methane derivatives possess a lesser toxic effect than ethane derivatives. Due to their strongly irritating properties, many chlorinated (as well as brominated) hydrocarbons are included in the composition of poisonous gases (chloroacetone, bromoacetone, chloromethyl, ethyl ketone, etc.). Of the numerous chlorinated hydrocarbons proposed and introduced into industry, the following are of the greatest practical importance due to their wide application in various industries: Methyl chloride, CH₃Cl, a colorless gas condensing into a liquid at -24°; it acquired its primary significance due to its wide introduction in the refrigeration industry; in the USA, where refrigerators with methyl chloride are especially common, numerous cases of poisoning have been observed; in the majority of cases, they were of a mild character, but severe (and fatal) cases have been described with convulsions, cyanosis, comatose and delirious states, visual disturbances, anuria, leukocytosis, and other phenomena. Carbon tetrachloride (tetrachloromethane), CCl₄, an easily evaporating liquid with an odor resembling chloroform; it is obtained by the action of chlorine or sulfur chloride on carbon disulfide. It is used for dissolving fats, rubber, sulfur chloride, resins; for degreasing metal parts in various industries, for extracting fats from bones, for hair washing; due to its absolute non-combustibility, it has found especially wide application in the production of fire extinguishers (when it comes into contact with red-hot iron or wood wool, it decomposes with the formation of phosgene). Compared to other chlorinated hydrocarbons, tetrachloromethane is slightly toxic: according to Lehmann, concentrations of 80–260 mg/l are required to produce mild narcosis in cats; according to Andreev, a concentration of 145 mg/l produces mild narcosis, and 400 mg/l causes death. The effect of tetrachloromethane is narcotic; at the same time, it irritates the skin and mucous membranes. During prolonged inhalation, dyspeptic disorders, headaches, and irritation of the mucous membranes of the upper respiratory tract and eyes were observed in workers; there are reports in the literature of isolated cases of liver disease, up to acute yellow atrophy. Tetrachloroethane, C₂H₂Cl₄, a colorless liquid with a faint odor resembling chloroform, boils at 146°, and is obtained by the action of chlorine on acetylene in the presence of a contact agent (iron). Tetrachloroethane is a very good solvent; during the war, it was widely used in the military industry—it was included in the composition of the varnish used to coat the wings of airplanes. However, due to its strong toxicity (up to 1916, it caused 70 cases of severe poisoning in England, 12 of which were fatal), its use in this industry has been banned in a number of countries; nevertheless, it is still used today in a number of industries: rubber, artificial silk, artificial pearl, motion picture film, for cleaning and degreasing metals, for filling fire extinguishers, etc.; from time to time, reports of poisoning cases arrive, and the poisonings are of a particularly severe character (often with a fatal outcome) among those working in small-scale industry (artificial pearl, footwear industry, where glue containing tetrachloroethane is used). The main phenomena in poisoning with tetrachloroethane are disorders of the gastrointestinal tract: loss of appetite, vomiting, diarrhea, jaundice, which can take (and often does take) a severe character with phenomena of serious intoxication—stupor, convulsions, comatose state; in those who died, yellow atrophy of the liver was found during autopsy. Damage to other organs was also observed—kidneys, heart, nervous system (tremor of the hands, disturbances of the sensory organs, dizziness, gait disorders, motor disturbances, etc.). Trichloroethylene, C₂HCl₃, a colorless liquid with a sweetish odor, boils at 87°, and is obtained by the action of chlorine on acetylene with subsequent splitting off of a particle of hydrochloric acid from the resulting tetrachloroethane. Due to its excellent dissolving properties, trichloroethylene has found very wide application in various industries, mainly in the metal industry—for cleaning large and especially small parts of dirt, grease, and lubricating oils, for degreasing objects in electroplating; furthermore, for the extraction of fats in oil mills from skin, bones, and fish waste; as a disinfectant, for filling fire extinguishers, etc. In the USSR, trichloroethylene was used for some time at fish-canning plants to extract fat from waste. Due to its wide distribution in industry, and moreover in a number of small-scale industries, trichloroethylene is the most dangerous of all chlorinated hydrocarbons—it causes the greatest number of poisonings. By 1931, information on 284 serious cases of poisoning had been collected from foreign literature, 25 of which ended in death; in the USSR, 20 cases of poisoning occurred in Astrakhan (during the processing of fish waste). In cases of poisoning, phenomena from the nervous system come to the fore: loss of consciousness, a state of stupor, general irritation of the nervous system, persistent damage to individual nerves, mainly the trigeminal nerve, atrophy of the optic nerve, etc. Trichloroethylene is especially dangerous due to the following additional properties: in a number of cases where it has the opportunity to undergo oxidation, it decomposes with the formation of phosgene (the fatal outcome in a number of cases is attributed to the action of the latter); it possesses an odor which many workers perceive as quite pleasant—they become accustomed to it and strive to remain in its atmosphere for longer (Trisucht). In the last few years, dichloroethane, or ethylene chloride, CH₂Cl-CH₂Cl, a colorless liquid with an odor resembling chloroform, boiling point 86°, has begun to be widely used in the USA as a solvent; it is obtained by the action of chlorine on ethylene. There is comparatively little data regarding its toxic effect; experimental studies by a number of authors (Dubois, Bintz, Miller, Lazarev, etc.) suggest that it is close to chloroform in its toxic properties; long-term observations on workers are currently absent. Prophylaxis. Since many chlorinated hydrocarbons are strong poisons that cause many serious (and often fatal) poisonings, vigilant supervision must be maintained over their introduction and use in industry. Especially serious attention should be paid to those branches of industry where it is impossible to implement airtight equipment and where the release of solvent vapors may occur in significant quantities; such are the industries: footwear, artificial leather (dermatin), shoe glues and creams, cleaning of clothes, etc.

In particular, regarding individual substances, the following must be pointed out: tetrachloroethane, as the most potent poison, may be permitted only in those industries where hermetically sealed equipment is available; the same should be said regarding trichloroethylene: work with it may be permitted only where it cannot be replaced by another solvent, in the presence of hermetically sealed equipment and constant supervision over it; the use of these substances cannot be permitted where they may decompose with the formation of phosgene; only those chlorinated hydrocarbons whose toxic properties and dangerous aspects have already been established, etc., may be permitted in industry. Since a number of chlorinated hydrocarbons will be introduced into production in the USSR in the coming years in connection with the widespread adoption of solvents in industry, the study of their toxic properties and the development of preventive measures must be carried out in advance. [Literature: Andreev V., Possibility of using carbon tetrachloride in aviation fire extinguishers and its effect on the human body, Hyg., Saf. and Labor Path., 1931, No. 2; Bernstein S., Trichloroethylene in factory practice, Hyg., Saf. and Labor Path., 1931, No. 3; Derrons T., Solvents, L., 1933; Korenman I., The solvent trichloroethylene and some of its properties, Hyg., Saf. and Labor Path., 1931, No. 3; Lazarev N. and Astrakhantsev P., Chemically harmful substances in industry, part 1, L., 1933; Proceedings of the I Congress of the Paint and Varnish Industry (articles by Astrakhantsev and Chelintsev), L., 1932; Hygiene du travail, Encyclopedic, v. I, pp. 834-38, Geneve, 1930; Stuber K., Gesundheitschadigungen bei der gewerblichen Verwendung des Trichlorathylens und die Moglichkeit ihrer Verhutung, Arch. f. Gewerbepath. u. Gewerbehyg., B. II, H. 3, 1931; Zangger H., Uber die modernen organischen Losungsmittel, ibid., B. I, H. 1, 1930; Zottinger F., Ein Beitrag zur gewerbepathologischen Bedeutung des Tetrachlorathans, ibid., B. II, H. 2, 1931. O. Leshchinovaya, D. Rozenbaum.] CHLOROMA, see Leukemia. CHLOROPHYLL (from Greek chloros - green and phyllon - leaf), a green pigment of plants; it is contained in cells in chlorophyll grains, consisting of a condensed protoplasmic stroma and the pigment itself, which is apparently present here in solid form or in the form of a concentrated colloidal solution. Chlorophyll is soluble in alcohol and many other organic solvents. An alcoholic solution is green in color with red fluorescence and a characteristic absorption spectrum. The sharpest absorption band is in the red rays between lines B and C, and there is significant absorption in the blue-violet part of the spectrum near line G and to the right of it. These optical properties of chlorophyll are very important in view of its role in photosynthesis (see Assimilation), which, as a photochemical reaction, proceeds most successfully in the absorbed rays, i.e., in the red ones (in green plants). By its chemical nature, chlorophyll, as clarified by the remarkable studies of Willstatter, is a magnesium-organic compound of the type of esters. Its acidic part, called chlorophyllin, is a dibasic acid, slightly different in the two known modifications of chlorophyll: C₃₂H₃₀ON₄Mg(COOH)₂ (in chlorophyll a) or C₃₂H₂₈O₂N₄Mg(COOH)₂ (in chlorophyll b). Attached to its acidic groups are two alcohol residues: one from methyl alcohol and the other from phytol - an unsaturated monohydric alcohol with a strongly branched chain of the composition C₂₀H₃₉OH.

The basic core of chlorophyllin (etiophyllin) appears in the form of 4 pyrrole groups, the nitrogens of which are connected to a magnesium atom, and the carbons carry one methyl and one ethyl group each. This structure of the central core significantly brings chlorophyll closer to hemoglobin (see), although in the latter, the central position is occupied not by magnesium but by iron, and the chromogenic group corresponding to chlorophyll is bound to a protein, and not in the form of an ester with alcohols. The physiological functions of both pigments are also opposite: the oxidative function of hemoglobin and the reductive function in the process of photosynthesis in chlorophyll. However, the chemical proximity of both pigments is also emphasized by the fact that, according to many indications, chlorophyll (in food) has a significant effect on hematopoiesis in animals (it is possible that the indicated effect depends on the pigments accompanying chlorophyll - xanthophyll and especially carotene, which, upon decomposition, yields vitamin A).

In green leaves, chlorophyll is contained in an amount of about 1% of the dry weight, with 3/4 being chlorophyll a and 1/4 being chlorophyll b. With few exceptions of some lower green plants, chlorophyll is formed only in the light. Grown in the dark, so-called etiolated plants contain a colorless chromogen - leucophyll, which in the light turns first into magnesium-containing green protochlorophyll, and then, by adding oxygen, into chlorophyll. It is interesting that the presence of iron is necessary for this process of greening, although iron does not enter into the chlorophyll molecule.