10. 5-(N-3,4,5,6-tetrahydrophthalimido)benzoic acid thiolester according to claim 1 of formula Id ##STR37## wherein n is zero, 1 or 2, R1 is C1 -C3 alkyl, R2 is fluorine, R3 is chlorine or bromine, A is a C1 -C4 alkylene bridge and R11 are independently of each other C1 -C4 alkyl or C1 -C4 alkoxy.