l radical is unsubstituted or substituted by a hydroxyl group and/or 1 or 2 C1-12 alkyl radicals, or a phenyl group, unsubstituted or substituted by one or more substituents selected from 1 or 2 halogen atoms, a cyano group, a hydroxyl group, 1 or 2 C1-12 alkyl radicals, 1 or 2 C1-12 alkoxy radicals, a phenyl group and the radicals R4 --O-- and R4 --SO2 --, wherein R4 is a phenyl group, unsubstitu