Compounds of the formula I ##STR1## wherein R.sub.1 is C.sub.1 -C.sub.18 alkyl, R.sub.2 is hydrogen or C.sub.1 -C.sub.18 alkyl, and A is a substituted primary or secondary aliphatic or alicyclic, aromatic or araliphatic amine, in which the substituents are identical or different, a heterocyclic amine or a hydrazine derivative.
                            式子I的化合物为##STR1##其中R.sub.1为C.sub.1 -C.sub.18烷基,R.sub.2为氢或C.sub.1 -C.sub.18烷基,A为取代的一级或二级脂肪或脂环、芳香或芳脂族胺,其中取代基相同或不同,或为杂环胺或
肼衍
生物。