Terephthaldialdehyde (67 g; 0.5 mole), ethanediol (31 g, 0.5 mole) and p-toluenesulphonic acid (0.5 g) in benzene (400 ml.) were boiled under reflux for 2 hours, with the removal of the water formed via a Dean and Stark separator. After cooling, the mixture was washed with dilute sodium bicarbonate solution (100 ml, 2% W/V), then saturated sodium chloride solution (2×100 ml.) and dried over magnesium sulphate. After filtration, the benzene solution was evaporated in vacuo to give a straw-coloured oil containing ca 70% of the desired aldehyde, viz: 4-(1,3-dioxol-2-yl)-benzaldehyde, which was reacted with 3-n-butylhydantoin as in Example 1.
