GB620030A - Preparation of guanidine salts - Google Patents

Abstract

Guanidine salts are prepared by the fusion of an ammonium salt with a cyanamide salt wherein the fusion is effected in the presence of urea in an amount at least equal to 15 per cent of the weight of the ammonium salt to reduce the fusion temperature of said ammonium salt to below about 120 DEG C., there being not more than 0.5 per cent water present. Preferably, the amount of urea present is from 15 to 45 per cent, the fused reaction mixture being maintained at a temperature within the range 110-135 DEG C. Under these conditions the reaction mixture is non-corrosive towards stainless steel and the substantial absence of water allows the use of thin-walled reaction vessels. Generally, the cyanamide salt, for example, calcium cyanamide, is added to the fused urea-ammonium salt mixture. Formation of dicyandiamide is minimized by limiting the period of heating, after the initial reaction, to one hour or the total period of addition and heating to not more than two hours. An excess of the ammonium salt may be used. In an example: nitrolime is slowly added to a fused mixture of urea and ammonium nitrate at 120 DEG C., and the resulting product is dissolved in water, the calcium present removed as the carbonate and the solution then cooled to crystallise out the guanidine nitrate which is removed. The final filtrate containing the urea is evaporated to dryness and, after fortification with additional ammonium salts, may be recycled in the process. Specification 507,498 and U.S.A. Specification 2,109,934 are referred to.