A mixture of 5.51 g (0.025 mole) of 2,6-di-tertiary-butyl-p-benzoquinone, 4.54 g (0.027 mole) of 3-(4-aminophenyl)propionic acid, 50 ml of tetrahydrofuran and 0.25 ml of boron trifluoride etherate was heated on a steam cone under a slow stream of nitrogen for two hours. The resulting solid was triturated with hexane, collected, rinsed with hexane and recrystallized from a mixture of ethyl acetate and hexane to give 5.1 g yellow 3-[4-(2,6-di-tertiary-butylcyclohexadienon-4-ylideneamino)phenyl]propionic acid, m.p. 165°-167° C. Analysis: Calculated for C23H29NO3 : % C, 75.2; % H, 8.0; % N, 3.8; Found % C, 74.8; % H, 7.9; % N, 3.7.
