Abstract: Novel process for the preparation of a monomeric acyl cyanide of the general formula ##STR1## in which R represents optionally substituted alkyl with up to 8 carbon atoms, optionally substituted cycloalkyl with 3 to 12 carbon atoms, optionally substituted aryl or an optionally substituted 5-membered or 6-membered heterocyclic radical, which optionally can be fused with a benzene ring,which process comprises heating the corresponding dimeric acyl cyanide of the general formula ##STR2## in which R has the meaning stated above, to a temperature of from 50.degree. to 300.degree. C. in the presence of a compound having a basic reaction and rapidly removing the monomeric acyl cyanide (I) formed from the reaction mixture.