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Originally appearing in Volume V22, Page 531 of the 1911 Encyclopedia Britannica.
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C2H6NC + CH3COCI --> C2H5NC(COCH3)Cl —~HCI + C2H6NH3 + CH3CO•CO2H. This view was confirmed by J. Wade (Journ. Chem. Soc., 1902, 81, p. 1596) who showed that the products obtained by the action of alkyl iodides on the isonitriles in alcoholic solution at roe C. yield amine hydroidides and formic acid when hydrolysed. Such a reaction can only take place if the addition of the alkyl group takes" place on the nitrogen atom of the isonitrile, from which it follows that the nitrogen atom must be trivalent and consequently the carbon atom divalent. The reactions may probably be represented as follows: C2H6NC+C2H5I+4C2H6OH=C2H5NH2•HI+HCO2C2H5+2 (C2H5)2O, C2H6NC(+C2HSI)-3C2H6N(C2H5•I)C(+3C2H5OH) -(C2H5)2NH•HI+ H•CO2C2H5 + (C2H5)2O. The isonitriles dissolve silver cyanide readily, forming a soluble silver salt (cf. KNC). At 200° C. the isonitriles are converted into nitrites. Constitution of Metallic Cyanides.—Considerable discussion has taken place as to the structure of the metallic cyanides, since potassium cyanide and silver cyanide react with alkyl iodides to form nitriles and isonitriles respectively, thus apparently pointing to the fact that these two compounds possess the formulae KCN. and AgNC. The metallic cyanides are analogous to the alkyl isocyanides, since they form soluble double silver salts, and the fact that ethyl ferrocyanide on distillation yields ethyl isocyanide also points to their isocyanide structure. J. Wade (loc. cit.) explains the formation of nitriles from potassium cyanide, and of isonitriles from silver cyanide by the assumption that unstable addition products are formed, the nature of which depends on the relative state of unsaturation of the carbon and nitrogen atoms under the varying conditions : KNC-KN:C(:C2H51) –)KI+C2HsCN, AgNC -AgN(:C2HsI)C-AgI +C2H5NC; that is, when the metal is highly electro-positive the carbon atom is the more unsaturated, the addition takes place on the carbon atom, and nitriles are produced. The same type of reaction occurs when the metal is relatively electro-positive to the added radical, for example, with ethyl isocyanide and acetyl chloride (see above) ; compare also AgNC --AgN(:Cl•000H3)C -->AgCl+CHa000N. On the other hand, when there is but little electro-chemical difference between the radical of the cyanide and that of the reacting compound then the nitrogen atom is the more unsaturated element and isonitriles are produced. This explanation also accounts for the formation of nitriles by the diazo reaction, thus : C6H1N2CI+CuNC–4CuN:C•CI•N2•C,HS~CuCl•}• N :C•N2•CoH6- >C6HsCN+N2. Detection.—The metallic cyanides may be detected by adding ferrous sulphate, ferric chloride, and hydrochloric acid to their solution, when a precipitate of.Prussian blue is produced; if the original solution contains free acid it must be neutralized by caustic potash before the reagents are added. As an alternative test the cyanide may be decomposed by dilute hydrochloric acid, and the liberated hydrocyanic acid absorbed in a little yellow ammonium sulphide. The excess of reagent is removed by evaporation and a small quantity of a ferric salt added, when a deep red colour is produced. Silver nitrate gives a white precipitate with cyanides, soluble in excess of potassium cyanide. The amount of hydrocyanic acid in a solution may be determined by adding excess of caustic potash and a small quantity of an alkaline chloride, and running into the dilute solution standard silver nitrate until a faint permanent turbidity (of silver chloride) is produced, that is, until the reaction, 2KNC+AgNOa=KAg(NC)2+KNO3, is completed. See R. Robine and M. Lengler, The Cyanide Industry, 1906 (Eng. trans. by J. A. Le Clerc) ; W. Bertelsmann, Die Technologie der Cyanverbindungen,1906. Pharmacology, Therapeutics and Toxicology of Hydrocyanic Acid.—The pharmacopoeial preparations of this acid are a 2% solution, which is given in doses of from two to six minims, the tinctura chloroformi et morphinae composita, which contains a half-minim of this solution in each ten minims, and the aqua laurocerasi, which owes its virtues to the presence of this acid, and is of inconstant strength, besides being superfluous. The acid is also the active ingredient of the preparations of Virginian Prune, to which the same strictures apply. The simple cyanides share the properties of the acid, except those of platinum and iron. With these exceptions, the simple cyanides are readily decomposed even by carbonic acid, free prussic acid being liberated. The double cyanides are innocuous. Hydrocyanic acid is a protoplasmic poison, directly lethal to all living tissues, whether in a plant or an animal. It is by no means the most powerful poison known, for such an alkaloid as pseud-aconitine, which is lethal in dose of about 1/200 of a grain, is some hundreds of times more toxic, but prussic acid is by far the most rapid poison known, a single inhalation of it producing absolutely instantaneous death. The acid is capable of passing through the unbroken skin, where-upon it instantly paralyses the sensory nerves. It is very rapidly absorbed from raw surfaces and may thereby cause fatal consequences. It is naturally an antiseptic. The therapeutic applications of the drug are based entirely upon its anaesthetic or anodyne power. A lotion containing ten minims of the dilute acid to an ounce of water and glycerin will relieve itching due to any cause; and is useful in some forms of neuralgia. It must never be employed when the skin is abraded. The diluted acid is used internally to relieve vomiting or gastric pain. It is also added to cough mixtures, when the cough is of the dry, painful kind, which serves no purpose, as nothing is expectorated. Such a cough is relieved by the sedative action on the central nervous system. Toxicology.—Instantaneous death results from taking the pure acid. The diluted form, in toxic quantities, will cause symptoms usually within a few seconds. The patient is quite unconscious, the eyes are motionless, the pupils dilated, the skin cold and moist, the limbs relaxed, the pulse is slow and barely perceptible, the respirations very slow and convulsive. Post mortem, the body is livid, and the blood very dark. There may be an odour of prussic acid, but this soon disappears. Treatment is only rarely of use, owing to the rapidity of the toxic action. The patient who survives half-an-hour will probably recover, as the volatile acid is rapidly excreted by the lungs. The drug kills by paralysing the nervous arrangements of the heart and respiration. The appropriate drug is therefore atropine, which stimulates the respiration and prevents the paralysis of the heart. One-fiftieth of a grain must be immediately injected subcutaneously. The stomach must be washed out and large doses of emetics given as soon as possible. Every second is of consequence. Ammonia should be given by inhalation, and artificial respiration must never be forgotten, as by it the paralysed breathing may be compensated for and the poison excreted. The use of chemical antidotes, such as iron salts, is futile, as the drug has escaped into the blood from the stomach long before they can be administered.
End of Article: C2H6NC

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