Carbon oxychloride (COCl₂, carbonyl dichloride, phosgene) is produced by direct combination of chlorine and carbonic oxide in presence of animal charcoal. Phosgene is itself a very poisonous gas which, in addition to the poisonous qualities of carbonic oxide (which have to be borne in mind in view of the method of manufacture), acts as an irritant of the mucous membranes. Commercially it is in solution in toluene and xylene, from which the gas is readily driven off by heating. It is used in the production of various colours, such as crystal violet, Victoria blue, auramine, &c.
A fatal case of phosgene gas poisoning in the report of the Union of Chemical Industry for 1905 deserves mention. The phosgene was kept in a liquefied state in iron bottles provided with a valve under 2·3 atm. pressure. The valve of one of these bottles leaked, allowing large escape into the workroom. Two workers tried but failed to secure the valve. The cylinder was therefore removed by a worker, by order of the manager, and placed in a cooling mixture, as phosgene boils at 8° C. The man in question wore a helmet into which air was pumped from the compressed air supply in the factory. As the helmet became obscured through moisture after five minutes the worker took it off. A foreman next put on the cleaned mask, and kept the cylinder surrounded with ice and salt for three-quarters of an hour, thus stopping the escape of gas. Meanwhile, the first worker had again entered the room, wearing a cloth soaked in dilute alcohol before his mouth, in order to take a sack of salt to the foreman. An hour and a half later he complained of being very ill, became worse during the night, and died the following morning. Although the deceased may have been extremely susceptible, the case affords sufficient proof of the dangerous nature of the gas, which in presence of moisture had decomposed into carbonic acid and hydrochloric acid; the latter had acutely attacked the mucous membrane of the respiratory passages and set up fatal bronchitis. Further, it was found that the leaden plugs of the valves had been eroded by the phosgene.
Three further cases of industrial phosgene poisoning have been reported,[9] one a severe case in which there was bronchitis with blood-stained expectoration, great dyspnœa, and weakness of the heart’s action. The affected person was successfully treated with ether and oxygen inhalations. Phosgene may act either as the whole molecule, or is inhaled to such degree that the carbonic oxide element plays a part.
In another case of industrial phosgene poisoning the symptoms were those of severe irritation of the bronchial mucous membrane and difficulty of breathing.[10] The case recovered, although sensitiveness of the air passages lasted a long time.
Carbon chlorine compounds (aliphatic series).—Methyl chloride (CH₃Cl) or chlormethane is prepared from methyl alcohol and hydrochloric acid (with chloride of zinc) or methyl alcohol, salt, and sulphuric acid. It is prepared in France on a large scale from beetroot vinasse by dry distillation of the evaporation residue. The distillate, which contains methyl alcohol, trimethylamine, and other methylated amines, is heated with hydrochloric acid; the methyl chloride so obtained is purified, dried and compressed. It is used in the preparation of pure chloroform, in the coal-tar dye industry, and in surgery (as a local anæsthetic). In the preparation of methyl chloride there is risk from methyl alcohol, trimethylamine, &c. Methyl chloride itself is injurious to health.
Methylene chloride (CH₂Cl₂, dichlormethane) is prepared in a similar way. It is very poisonous.
Carbon tetrachloride (CCl₄, tetrachlormethane) is technically important. It is prepared by passing chlorine gas into carbon bisulphide with antimony or aluminium chloride. Carbon tetrachloride is a liquid suitable for the extraction of fat or grease (as in chemical cleaning), and has the advantage of being non-inflammable. Carbon tetrachloride, so far as its poisonous qualities are concerned, is to be preferred to other extractives (see Carbon Bisulphide, Benzine, &c.); for the rest it causes unconsciousness similar to chloroform.
When manufactured industrially, in addition to the poisonous effect of chlorine, the poisonous carbon bisulphide has also to be borne in mind.
Ethyl chloride (C₂H₅Cl) is made in a way analogous to methyl chloride by the action of hydrochloric acid on ethyl alcohol and chloride of zinc. It is used in medicine as a narcotic.
Monochloracetic acid.—In the preparation of monochloracetic acid hydrochloric acid is developed in large quantity. From it and anthranilic acid artificial indigo is prepared (according to Heuman) by means of caustic potash.