Imidazolidine-4,5-dione dicarboxylic acids and derivatives

A dicarboxylic acid or derivative which contains an imidazolidine-4, 5-dione ring, of the formula I ##STR4## wherein X represents nitrile, carboxyl, chlorocarbonyl, phenoxycarbonyl or alkoxycarbonyl of 1 to 10 carbon atoms in the alkoxy moiety,

• R represents alkylene of 1 or 2 carbon atoms in the chain, said alkylene substituted with alkyl groups of 1 to 6 carbon atoms, cyclohexylene, phenylene or benzylene the methyl group of which is attached to the nitrogen atom, each of R.sup.1 and R.sup.2 independently represents hydrogen, alkyl of 1 to 18 carbon atoms, cycloalkyl of 5 to 8 ring members, phenyl, or together R.sup.1 and R.sup.2 represent tetramethylene, pentamethylene, hexamethylene or heptamethylene, with the proviso that, if R represents phenylene, R.sup.1 is a hydrogen atom and R.sup.2 is alkyl of 1 to 18 carbon atoms or cycloalkyl of 5 to 8 ring members.