Cyanide Compounds

Cyanide compounds, otherwise cyanogen compounds, constitute an extensive group of compounds characterized by the presence of the monovalent radical -CN. The latter resembles halogens in its chemical properties and is sometimes classified among the so-called pseudohalogens (cf. the similarity of salts, for example, of silver chloride and silver cyanide, the similarity in the formation of hypochlorous and cyanic acids, etc.). The chemical peculiarities of cyanide compounds are the ease of formation of complex compounds, the ease of polymerization, and the existence of isomers of the cyanide or nitrile type with the formula RCN—see Nitriles—and of the isonitrile or carbylamine type with the formula RNC. C. compounds represent almost exclusively a toxicological interest for practical medicine, connected with the possibility of the formation in the body of C. compounds of highly poisonous hydrocyanic acid (see). In connection with this, the biological activity of C. compounds, depending on other inherent physical-chemical properties, is not considered here (for example, the laxative effect of yellow blood salt, the oxidizing effect of red blood salt, which converts hemoglobin into methemoglobin, or finally the formation of dermatitis caused by calcium cyanamide). The first studies on the comparative toxicity of cyanide compounds, belonging to the famous Russian toxicologist E.V. Pelikan (1856), were so substantial that "according to Rent (Hunt, 1920), numerous subsequent works on cyanide compounds have added nothing fundamentally new in this respect." The toxicological classification of cyanide compounds can be presented as follows: 1) Hydrocyanic acid, cyanogen (otherwise dicyan) (CN)₂ and halogen C. compounds: cyanogen chloride, cyanogen bromide, cyanogen iodide (cyanogen fluoride is not yet known). Cyanogen gas, acting similarly to hydrocyanic acid; halogen cyanides, in addition to the toxic action inherent in hydrocyanic acid, are characterized by strongly irritating (lachrymatory) properties. 2) Simple cyanides of alkali and alkaline earth metals, easily soluble in water and highly poisonous. Among them, barium cyanide is the most stable compound. 3) Simple cyanides of heavy metals, soluble in dilute acids (cyanides of silver, copper, zinc, lead), poisonous when introduced into the stomach, as they release hydrocyanic acid in its acidic environment. Mercury cyanide, unlike cyanides of other heavy metals, soluble in water, is especially poisonous. 4) Simple cyanides of heavy metals, insoluble in dilute acids (cyanides of iron, cobalt, chromium, gold, platinum), not poisonous. 5) Complex cyanide compounds of heavy (silver, zinc, nickel, mercury) and alkali metals (so-called double cyanides), slightly soluble in water, but releasing hydrocyanic acid when in contact with dilute acids (poisonous). 6) Potassium ferricyanide, K₃Fe(CN)₆, the so-called red blood salt, or "red potassium ferrocyanide," and potassium ferrocyanide, K₄Fe(CN)₆, the so-called yellow blood salt, and similar compounds of cobalt, despite the relatively greater stability of these compounds with respect to dilute acids, under certain conditions when introduced into the stomach can cause poisoning. 7) Particularly numerous is the group of organic compounds containing the cyan radical. With insufficient study of this group from a toxicological point of view, it should be noted that the release of hydrocyanic acid in the body occurs in nitriles and dinitriles of fatty acids (acetonitrile, propionitrile, propanedinitrile, etc.) and apparently does not occur in benzonitrile and toluonitrile. Depending on the rate of release of hydrocyanic acid, the picture of poisoning by C. compounds can vary considerably. In poisonings by C. compounds that release hydrocyanic acid in the body, thiocyanate compounds are found in the urine or other secretions, and compounds containing labile sulfur (sodium hyposulfite, etc.) demonstrate a detoxifying effect (see Hydrocyanic acid). This release of hydrocyanic acid in the case, for example, of acetonitrile (CH₃CN) depends on metabolism, diet, hormonal influences, which is why Gent proposed the so-called acetonitrile test, which makes it possible in experiments on mice to detect the activity of thyroid preparations by reducing the toxicity of acetonitrile. Some C. compounds, not releasing hydrocyanic acid, but in which the CN radical (similar to halogens) increases their irritating properties, in imperialist countries were used or proposed as combat poison gases (see). These cyanide compounds include benzyl cyanide bromide, diphenylcyanarsine, etc. For medical purposes, sodium and potassium cyanides are sometimes used. Potassium cyanide (Kalium cyanatum), a white large-crystalline powder (or a fused amorphous mass); in air containing even traces of moisture, it smells of hydrocyanic acid, displaced from the salt by the carbon dioxide of the air (which is why it gradually turns into potassium carbonate with poor storage). Under the influence of strong acids (for example, dilute sulfuric acid), it quickly releases hydrocyanic acid (a method used to obtain the latter for disinfestation purposes). It can be used for the same indications as bitter almond water, in doses of 0.005-0.01 (in solution). Maximum single dose 0.03, daily 0.5 (dosage given according to additions to the German pharmacopoeia). Lethal dose when taken internally 0.1-0.2 g. Externally in 0.2-0.3% solutions for itching (with caution!). Sodium cyanide (Natrium cyanatum); physical-chemical properties and application coincide with those of the previous salt. Sodium cyanide, being a salt of a lighter metal, is more poisonous than potassium cyanide. Other cyanide compounds, with the exception of mercury cyanide (see), are of greater interest not for therapeutic medicine, but for professional toxicology due to the possibility of cyanide poisonings during work on disinfestation, deratization, during the extraction of precious metals from their ores by the cyanide method, during galvanoplasty procedures, etc.