. . . . "4-phenoxybutyl, heptyl, octyl or 2-ethylhexyl.If R.sup.1 is substituted C.sub.1 -C.sub.6 -alkyl, suitable substituents are, for example, C.sub.1 -C.sub.4 -alkoxy, phenoxy, phenyl which may be substituted by C.sub.1 -C.sub.4 -alkyl, halogen, in particular fluorine, chlorine or bromine orC.sub.1 -C.sub.4 -alkoxy, or are C.sub.1 -C.sub.4 -mono- or dialkylcarbamoyl, pyrrolidinocarbonyl, piperidinocarb" .