Chlorinated Hydrocarbons

CHLORINATED HYDROCARBONS. From the extensive group of organic substances used in industry as solvents, a large group of chlorinated hydrocarbons should be distinguished, which, thanks to their special technical properties (good solvency combined with non-flammability and non-inflammability), found extensive application in a very large number of industries in the USA and Western European countries: machine building, aviation, automobile construction, electroplating, footwear, artificial leather, canning, oil extraction, and many others; they are also used for cleaning clothes and linen, for washing hair, for disinfection and disinsection, for filling fire extinguishers, for refrigeration, and other purposes. Chlorinated derivatives of methane (methyl chloride, dichloromethane, chloroform, carbon tetrachloride), acetylene (vinyl chloride, dichloroethylene, trichloroethylene, perchloroethylene, tetrachloroethane, pentachloroethane), aromatic hydrocarbons (mono- and dichlorobenzene), and many others are used. In the USSR, chlorinated hydrocarbons are currently used in small quantities, 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 safety measures. Compared to the parent hydrocarbons, they possess a much more pronounced action on the organism; this action is manifested in irritation of the mucous membranes and in damage to the central nervous system; in the picture of poisoning, narcotic phenomena alternating with signs of excitement come to the fore; furthermore, chlorinated hydrocarbons have a strong effect on parenchymatous organs (heart, liver, pancreas, etc.; chloroform, carbon tetrachloride, and tetrachloroethane act especially sharply on the liver). Methane derivatives possess less toxic action than ethane derivatives. Due to their strongly irritating properties, many chlorinated (as well as brominated) hydrocarbons are part of poisonous gases (chloroacetone, bromoacetone, chloromethyl, ethyl ketone, etc.). Of the numerous chlorinated hydrocarbons proposed and introduced into industry, the following have the greatest practical significance, due to their wide application in various industries: methyl chloride, CH₃Cl, a colorless gas condensing into a liquid at -24°; its main significance was acquired due to its wide introduction into refrigeration; in the USA, where refrigerators with methyl chloride are especially widespread, numerous cases of poisoning have been observed; in most cases they were of a mild character, but severe (and fatal) cases with convulsions, cyanosis, coma, and delirious state, disturbances of vision, anuria, leukocytosis, and other phenomena have been described. Carbon tetrachloride (tetrachloromethane), CCl₄, a readily evaporating liquid with a smell reminiscent of 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 productions, for extracting fats from bones, for washing hair; due to its absolute non-flammability, it has found especially wide application in the production of fire extinguishers (when it falls on red-hot iron, alcohol decomposes with the formation of phosgene). Compared to other chlorinated hydrocarbons, tetrachloromethane is slightly poisonous: according to Lehmann, concentrations of 80-260 mg/l are required to produce light narcosis in cats; according to Andreev, a concentration of 145 mg/l produces light narcosis, 400 mg/l causes death. The action of tetrachloromethane is narcotic; at the same time it irritates the skin and mucous membranes. With prolonged inhalation, workers observed dyspeptic disorders, headaches, irritation of the mucous membranes of the upper respiratory tract and eyes; in the literature there are reports of isolated cases of liver disease, up to acute yellow atrophy. Tetrachloroethane, C₂H₂-Cl₄, a colorless liquid with a faint smell reminiscent of chloroform, boils at 146°, is obtained by the action of chlorine on acetylene in the presence of a contact (iron). Tetrachloroethane is an excellent solvent; during the war it was widely used in the war industry—it was part of the lacquer used to cover airplane wings. However, due to its high toxicity (before 1916 in England it caused 70 cases of severe poisoning, of which 12 were fatal), its use in this industry is prohibited in a number of countries; nevertheless, it is still used in a number of industries: rubber, artificial silk, artificial pearl, film, for cleaning and degreasing metals, for filling fire extinguishers, etc.; from time to time reports of cases of poisoning arrive, and the poisoning has a particularly severe character (often with a fatal outcome) among workers in small industries (artificial pearl, footwear production, 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 may take (and often takes) a severe character with signs of serious intoxication—stupor, convulsions, coma; in those who died at autopsy, yellow atrophy of the liver was found. Damage to other organs was also observed—kidneys, heart, nervous system (tremor of hands, disturbances in sensory organs, dizziness, disturbances of gait, motor disorders, etc.). Trichloroethylene, C₂HCl₃, a colorless liquid with a sweetish smell, boils at 87°, is obtained by the action of chlorine on acetylene followed by the separation of a particle of hydrochloric acid from the resulting tetrachloroethane. Thanks to its excellent solvency, trichloroethylene has found very wide application in various industries, mainly in the metal industry—for cleaning large and especially small parts from contamination, grease, lubricating oils, for degreasing objects in electroplating; furthermore, for extracting fats at oil mills from skin, bones, fish offal; as a disinsectant, for filling fire extinguishers, etc. In the USSR, trichloroethylene was used for some time at fish canning plants for extracting fat from offal. Due to its wide distribution in industry, and indeed in a number of small productions, trichloroethylene is the most dangerous of all chlorinated hydrocarbons—it causes the greatest number of poisonings. By 1931, data from foreign literature collected 284 serious cases of poisoning, of which 25 ended in death; in the USSR there were 20 cases of poisoning in Astrakhan (in processing fish offal). In poisoning, phenomena on the nervous system come to the fore: loss of consciousness, state of stupor, general irritation of the nervous system, persistent damage to individual nerves, mainly the trigeminal, atrophy of the optic nerve, etc. Trichloroethylene is especially dangerous due to the following properties: in a number of cases where it has the opportunity to undergo oxidation, it decomposes with the formation of phosgene (the action of the latter is attributed to the fatal outcome in a number of cases); it possesses a smell which many workers perceive as very pleasant—they get used to it and strive to stay longer in its atmosphere (Trisucht). In the last few years, dichloroethane, or vinyl chloride, CH₂Cl-CH₂Cl, a colorless liquid with a smell reminiscent of chloroform, boiling point 86°, has been widely used in the USA as a solvent. Data on its toxic action are relatively scarce; experimental studies by a number of authors (Du Bois, Binz, Miller, Lazarov, etc.) indicate that it is close to chloroform in its toxic properties; long-term observations on workers are still lacking. Prevention. Since many chlorinated hydrocarbons are strong poisons giving many serious (and often fatal) poisonings, vigilant supervision must be exercised over their introduction and use in industry. Particular serious attention must be paid to those branches of industry where it is impossible to achieve hermetic equipment and where the release of solvent vapors can occur in significant quantities; such productions are: footwear, artificial leather (dermatin), shoe glues and creams, cleaning of clothes, etc.

CHLOROPHYLL (from Greek chloros-green and phyllon-leaf), the green pigment of plants; it is contained in the cells in chlorophyll grains, consisting of a compacted protoplasmic stroma and the pigment itself, which apparently exists here in a solid form or as a concentrated colloidal solution. Chlorophyll dissolves in alcohol and many other organic solvents. An alcoholic solution is green in color with a red fluorescence and a characteristic absorption spectrum. The most intense absorption band is in the red rays between the lines B and C, and there is significant absorption in the blue-violet part of the spectrum near the 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 (in green plants). According to its chemical nature, chlorophyll, as has been elucidated by the remarkable researches of Willstatter, represents a magnesium-organic compound of the type of complex esters. Its acid part, called chlorophyllin, is a dibasic acid, somewhat different in the two known modifications of chlorophyll: C32H30ON4Mg(COOH)2 (in chlorophyll a) or C32H28O2N4Mg(COOH)2 (in chlorophyll b). To its acid groups -COOH and -CH2CH3 - are attached two alcoholic residues: one from methyl alcohol and the other from phytol, an unsaturated monatomic alcohol with a strongly branched chain of composition (see scheme) C20H39OH. In turn, the basic nucleus of chlorophyllin (pheophytin) is represented by four pyrrole groups, the nitrogens of which are connected to a magnesium atom, and the carbons bear one methyl and one ethyl group. This structure of the central nucleus brings chlorophyll very close to hemoglobin (see), although in the latter the central position is occupied not by magnesium but by iron, and the corresponding chromophoric group of chlorophyllin is connected with a protein, not in the form of an ether 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 further emphasized by the fact that, according to many indications, chlorophyll (in food) exerts a significant effect on blood formation in animals (it is possible that the indicated effect depends on the accompanying chlorophyll pigments - xanthophyll and especially carotin, which, decomposing, gives vitamin A). In green leaves, chlorophyll is contained in an amount of about 1% of the dry weight, of which 3/4 falls on chlorophyll a and 1/4 on chlorophyll b. With few exceptions of certain lower green plants, chlorophyll is formed only in light. Plants grown in the dark, the so-called etiolated plants, contain a colorless chromogen - leucophyll, which on light is first transformed into a magnesium-containing green protochlorophyll, and then, by attaching oxygen, into chlorophyll. It is interesting that for this process of greening the presence of iron is necessary, although iron does not enter the molecule of chlorophyll.