GB910876A - Improvements in or relating to the preparation of cyano compounds - Google Patents

Abstract

The invention comprises 4-carboxy-2:6-dihalobenzonitriles and their sodium and potassium salts and C1-4 alkyl esters, and a method for preparing a 2:6-dihalobenzonitrile by heating a 4-carboxy-2:6-dihalobenzonitrile or a salt thereof to remove carbon dioxide from the carboxy group. The halogen is chlorine or bromine. 4-Amino benzoic acid is chlorinated or brominated with an alkali metal chlorate or bromate and acetic acid and sodium acetate, to give 4-carboxy-2:6-dihaloaniline, which is esterified either by saturating its solution in an alcohol of 1 to 4 carbon atoms with dry hydrogen chloride, or by reacting it with diazomethane to obtain the methyl ester. The ester is diazotized by reacting sodium nitrite solution with the ester in sulphuric acid at 0 DEG to 4 DEG C., and the resulting diazonium compound is reacted with sodium or potassium cuprous cyanide, or a mixture of sodium or potassium cyanide and cuprous cyanide, under alkaline conditions at 0 DEG to 20 DEG C., to obtain the ester of 4-carboxy - 2:6 - dihalobenzonitrile, which is hydrolysed by boiling with aqueous or alcoholic alkali metal hydroxide to a salt of 4-carboxy-2:6-dihalobenzonitrile. The salt may be converted to the acid by acidification. 2:6-Dihalobenzonitrile is obtained by heating the carboxy compound or its salt at 150 DEG to 250 DEG C. with a tertiary nitrogenous base, e.g. pyridine or quinoline, in the presence of finely divided metallic copper, copper bronze or a copper salt, e.g. copper sulphate, carbonate or chromite, and then removing the nitrogenous base by distillation or by precipitation with an acid and extracting the dihalobenzonitrile with a solvent e.g. ether. Examples describe the preparation of 4-carboxy-2:6-dichlorobenzonitrile and its methyl ester, and decarboxylation to obtain 2:6-dichlorobenzonitrile.