p consisting of a halogen atom, an alkyl radical with 1 to 5 carbon atoms, a phenyl radical, which may be substituted, an alkoxy radical with 1 to 5 carbon atoms and a phenoxy radical, which may besubstituted.Most preferably R is a phenyl or a substituted phenyl radical.Preferably R.sup.1 and R.sup.4 are each selected from the group consisting of an alkyl radical with 1 to 5 carbon atoms, an alken