GUANIDINE, a colourless, deliquescent, crystalline solid readily soluble in water or alcohol; it occurs in both vegetable and animal kingdoms. Guanidine, HN : C 2j is found in the juice of sugar beet, in etiolated vetch seedlings and in the embryo of the chick. It was first prepared by A. Strecker, who oxidized guanine with potassium chlorate and hydrochloric acid, and is also formed by oxidizing egg albumin or gelatin with a soluble permanganate. Many synthetic processes have been devised for the preparation of guanidine of which the best known is the heat ing of ammonium thiocyanate to 180-190 ° C; thiourea, formed as an intermediate product, changes into guanidine thiocyanate with elimination of hydrogen sulphide. E. A. Werner and J. Bell recommend the heating to 120° C of an intimate mixture of am monium thiocyanate and dicyanodiamide (obtained commercially from calcium cyanamide) . After heating for several hours, the melted mass is extracted with water, and the concentrated aque ous extracts give 9o% yields of guanidine thiocyanate (1920). Guanidine has strongly alkaline properties : it absorbs carbon diox ide from the air and forms well-defined crystalline salts with mineral and organic acids. Its relationship with the more com plex products of animal metabolism is shown by the fact that when its carbonate is condensed with methylglycine (sarcosine) it yields creatine and creatinine.
Guanidine has played an important part in the development of the chemistry of nitrogen compounds. Mixed with nitric and sul phuric acids it furnishes nitroguanidine, HN : C (colourless needles decomposing at which on reduc tion with zinc dust and acetic acid gives rise to aminoguani dine, HN :C This amino compound undergoes hydrolysis with dilute acids or alkalis in two stages, yielding first semicarbazide, (colourless prisms, m.p. 96° C), a valuable reagent for aldehydes and ketones, and secondly carbon dioxide, ammonia and hydrazine. The final stage of hy drolysis is of special interest as being one of the earlier methods adopted for the preparation of hydrazine, (J. Thiele, 1892). By the action of nitrous acid on aminoguanidine nitrate, diazoguanidine nitrate is produced, NH : C This diazo-compound is decomposed by caustic alkalis into cyan amide and an alkali salt of hydrazoic acid, another of the nitrogen hydrides.
See "Guanidine," Thorpe, Dictionary of Applied Chemistry (1922) ; E. Abderhalden, Biochemisches Handlex kon, vol. iv., 783 ; vol. ix., 187 (191I and 1915).