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A solution of 15.2 g (0.2 mol) of thiourea in 100 ml of water is introduced into a 1 liter three-necked flask equipped with a magnetic stirrer, a condenser and a dropping funnel, and 28.9 g (0.2 mol) of p-fluorobenzyl chloride are added all at once, at 50°-60° C. The mixture is heated to reflux temperature, boiling is maintained for about 15 minutes and the solution becomes limpid. Thereafter the solution is cooled and a solution of 32 g (0.8 mol) of NaOH in water is added dropwise at about 60° C. The whole is heated under reflux for about 30 minutes, the mixture is cooled and a solution of about 0.28 mol of sodium chloroacetate (obtained by neutralising 26.46 g of chloroacetic acid in 200 ml of water with 23.52 g of sodium bicarbonate) is added dropwise at 60°-70° C. Thereafter the whole is heated under reflux for 30 minutes and then cooled. The mixture is acidified with 3 N HCl and the oil which is obtained is taken up in methylene chloride, this mixture is washed with a dilute sodium bicarbonate solution, filtered over charcoal and acidified once more with 3 N HCl; p-fluorobenzylthioacetic acid is thus precipitated, and is filtered off. After recrystallising from cyclohexane, 33.4 g (yield: 83%) of the said acid are collected. Instantaneous melting point: 68°-69° C.

1. customequipped with a magnetic stirrer, a condenser and a dropping funnel
2. temperatureThe mixture is heated
3. temperatureto reflux temperature
4. temperatureboiling is maintained for about 15 minutes
5. temperatureThereafter the solution is cooled
6. temperatureThe whole is heated
7. temperatureunder reflux for about 30 minutes
8. temperaturethe mixture is cooled
9. temperatureThereafter the whole is heated
10. temperatureunder reflux for 30 minutes
11. temperaturecooled
12. customthe oil which is obtained
13. washthis mixture is washed with a dilute sodium bicarbonate solution
14. filtrationfiltered over charcoal
15. customp-fluorobenzylthioacetic acid is thus precipitated
16. filtrationis filtered off