Hydrogen Bromide → 3,4-Methylenedioxybenzylthio-acetic acid

참여 물질

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A solution of 18.24 g (0.24 mol) of thiourea in 104 ml of 48% strength hydrobromic acid and 20 ml of water is introduced into a one liter three-necked flask equipped with a magnetic stirrer and a condenser. The mixture is heated to 60° C. and 30.4 g (0.2 mol) of piperonyl alcohol are introduced. The temperature is raised to 95° C. and the mixture is left to cool. Crystals of the thiouronium salt appear; these are filtered off and dried. The precipitate thus obtained is introduced into a 500 ml three-necked flask with 60 ml of sodium hydroxide solution. The mixture is heated to 70° C. and 15.6 g (0.164 mol) of chloroacetic acid in 30 ml of water are added dropwise. Thereafter the whole is heated under reflux for half an hour and then cooled. The mixture is acidified with 3 N HCl, the precipitate obtained is redissolved in a dilute bicarbonate solution, and the solution is washed with methylene chloride, filtered over charcoal and acidified once more with 3 N HCl in order to precipitate 3,4-methylenedioxybenzylthio-acetic acid, which is filtered off. After recrystallisation from a diisopropyl ether/petroleum ether mixture (1:1 v/v), 18.2 g (yield 40%) of the said acid are collected (instantaneous melting point=87° C.).

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