ent to K1 and of the general formulae given below, described in the form of the free acid ##STR4## in which B, R5, R6 and R7 are as defined above and R represents a hydrogen atom or a lower alkyl group, such as a methyl group, and p represents the number 1 or 2, examples which may be given of the abovementioned aminonaphtholsulfonic acid radical being the bivalent radicals of the formulae ##STR5##