Ladislas et al., European Patent Application 446047A1, published Sep. 11, 1991, disclose compounds of the formula: ##STR1## where R1 is a hydrogen atom or a C1 -C5 alkyl or alkoxy group, and R2 is a monovalent C8 -C20 alkyl or C9 -C20 alkenyl group, optionally substituted with OH or COOH group, or R2 is a group with the formula: ##STR2## where R3 is a divalent straight or branched C2 -C6 saturated