ving from 1 to 4 carbon atoms, halogen atoms, the --OH radical, the --C.tbd.N radical, the --NO2 radical, and the radical of the formula --NR1 R2, in which R1 and R2, which may be identical or different, represent a linear or branched chain alkyl radical having from 1 to 4 carbon atoms, M is an inorganic or organic cationic radical selected from the group consisting of the cations derived from the