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Originally appearing in Volume V27, Page 794 of the 1911 Encyclopedia Britannica.
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CONH -- NH2. CO2R-> NH2CO• NH •CO2R; by the action of chlorcarbonic esters on urea (H. Schiff, Ann., 1896, 291, p. 367) ; and by the action of urethanes on urea chloride (L. Gattermann, Bee., 1888, 21, p. 293 R). They are readily decomposed by alkalis, yielding cyanuric acid and ammonia. Biuret (allophanamide), NH2•CO•NH•CO•NH2, is formed by heating urea; by the action of ammonia on allophanic ester; and by heating urea to 14o° C. and passing chlorine into the melt at 14o-15o° C. (J. Thiele, Ann., 1898, 303, p. 95 Anm.). It crystallizes in needles which melt at 19o° C. (with decomposition), and is readily soluble in hot water. When heated strongly it is decomposed into ammonia and cyanuric acid. Baryta water hydrolyses it to carbon dioxide, ammonia and urea. With silver nitrate and caustic soda it yields a silver salt, Ag2C2HaN202• With nitric acid in the presence of sulphuric acid it yields a nitro derivative. Thiourea, or sulphocarbamide, CS(NH2)2, is formed by pro-longed fusion of ammonium thiocyanate (E. Reynolds, Ann., 1869, 15o, p. 224), by passing sulphuretted hydrogen into an ethereal solution of cyanamide (E. Baumann, Ber., 1873, 6, p. 1375), or by heating isopersulpho-cyanic acid (F. D. Chattaway, Jour. Chem. Soc., 1897, 71, p. 612). It crystallizes in thick prisms which melt at 18o° C. and is readily soluble in water. When heated for some time with water to 14o° C. in a sealed tube, it is transformed into ammonium thiocyanate, a similar result being obtained by heating the base alone for some hours to 16o-17o° C. On heating alone for some hours to 17o-18o° C. it is converted into guanidine thiocyanate. It is hydrolysed by alkalis, giving carbon dioxide, ammonia and sulphuretted hydrogen. It is readily desulphurized by silver oxide, mercuric oxide or lead oxide. Potassium permanganate oxidizes it to urea (R. Maly, Monats., 1890, 11, p. 278). It acts as a weak base and forms salts with one equivalent of an acid. The alkyl derivatives of thiourea are obtained by the action of ammonia and of primary and secondary amines on the mustard oils (A. W. Hofmann, Ber., 1867, 1, p. 27): CSNR+NH3=NH2•CS•NHR; CSNR+NH2R=R•NH•CS•NHR, or by heating the amide salts of the alkyl dithio-carbaminic acids, viz., NR•CS•S(NH,R). The monoalkyl derivatives are desulphurized by lead hydroxide in the presence of sodium carbonate, the a!3 dialkyl and trialkyl derivatives being unaffected (A. E. Dixon, Jour. Chem. Soc., 1893, 63, p. 325). The dialkyl thioureas when digested with mercuric oxide and amines give guanidines. CS(NHR)2+NH2R+HgO->HgS+RN:C(NHR)2. Thiourea and many of its unsymmetrical derivatives have marked physiological action; thiourea causes a slowing of the pulse and respiration, cardiac failure, and death in convulsions; phenyl-, ethyl- and acetyl-thiourea are actively toxic. The most important derivative pharmacologically is allyl-thiourea, also known as thiosinamine or rhodallin, NH2•CS•NH.CH2.CH:CI-I2. Thiosemicarbazide, NH2.CS•NH.NH2, prepared from hydrazine sulphate, potassium carbonate and thiocyanate (N. Freund, Ber., 1895, 28, p. 946; 1896, 29, p. 2501), crystallizes in long needles, which melt at 181-183° C. The addition of sodium nitrite to an aqueous solution of its hydrochloride converts it into amido-triaz- N- N sulphol S< 1. The hydrochloride with potassium cyanate C(NH2) : N gives hydrazothio-carbonamide, NH2.CO.NH•NH•CS•NH2. Medicine.-Urea has been given in medicine in doses of 10 to 6o grs. either in mixture or hypodermically. It has been used with success as an antiperiodic and antipyretic in ague, and also as a diuretic in gout and kidney affections. Thiosinamine is given internally in doses of z to I gr. in capsule. Larger doses usually upset the digestion. It has been used for the cure of lupus and of keloid, in which case it is administered hypodermically. In keloid 20 minims of a 1o%° solution is injected directly into the part. It causes a local reaction with absorption of the scar tissue. For this reason it is used to remove corneal opacities, deafness due to thickening of the membrane, stricture of the oesophagus and hypertrophy of the pylorus, it has also been successful in the treatment of adhesive parametritis. Fibrolysin is a modified form of thiosinamine made by mixing it with sodium salicylate Fibrolysin is freely soluble and may be given in hypodermic or intra-muscular injection. Like thiosinamine it has a specific action on scar tissue and has been used in urethral strictures. Both these preparations should only be used in cases where it is possible to exclude any tuberculous foci, or by their action in breaking down protective fibrous tissues they may cause a quiescent lesion to become active. In large doses toxic symptoms are produced, death following on coma.
End of Article: CONH
CONGRUOUS (from Lat. congruere, to agree)

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