a phenyl radical or a 4???-amino-phenyl radical; R2 is chosen from a hydrogen atom, a C1-C4 alkyl radical, a C1-C4 monohydroxyalkyl radical, a C2-C4 polyhydroxyalkyl radical, a (C1-C4)alkoxy(C1-C4)alkyl radical and a C1-C4 alkyl radical substituted with a nitrogenous group; R3 is chosen from a hydrogen atom, a halogen atom such as a chlorine, bromine, iodine or fluorine atom, a C1-C4 alkyl radical