4-(2,5-Dihydroxyphen-1-yl)-crotonic acid and its derivative (I) ##STR1## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are each H or C.sub.1 -C.sub.8 -alkyl, R.sup.5 is H, C.sub.1 -C.sub.30 -alkyl or C.sub.2 -C.sub.30 -alkenyl, and R' is H or an organic radical which can be split off hydrogenolytically, and a process for the preparation of the compounds I, wherein a hydroquinone II ##STR2## is reacted, in the presence of from 0.1 to 2 moles of a Lewis acid per mole of II, with (a) a vinylglycolic acid derivative IIIa ##STR3## or (b) a crotonic acid derivative IIIb ##STR4## where X is halogen, hydroxyl or C.sub.1 -C.sub.4 -alkoxy or acyloxy.
4-(2,5-二羟基苯基)-
巴豆酸及其衍
生物(I),其中R.sup.1、R.sup.2、R.sup.3和R.sup.4分别为H或C.sub.1-C.sub.8-烷基,R.sup.5为H,C.sub.1-C.sub.30-烷基或C.sub.2-C.sub.30-烯基,R'为H或可通过氢解裂的有机基,以及一种用于制备化合物I的方法,其中
氢醌II ##STR2## 在每摩尔II的存在下与(a)
乙烯基甘醇酸衍
生物IIIa ##STR3## 或(b)
巴豆酸衍
生物IIIb ##STR4## 反应,其中X为卤素、羟基或C.sub.1-C.sub.4-烷氧基或酰氧基。