NC(N)=[S:3].[CH3:5][O:6][C:7]1[CH:8]=[C:9]([CH:12]=[CH:13][C:14]=1[O:15][CH3:16])[CH2:10]Cl.[OH-].[Na+].Cl[CH2:20][C:21]([O-:23])=O.[Na+]>O>[CH3:5][O:6][C:7]1[CH:8]=[C:9]([CH:12]=[CH:13][C:14]=1[O:15][CH3:16])[CH2:10][CH2:20][C:21]([OH:23])=[S:3]13.07 g (0.172 mol) of thiourea and 86 ml of water are introduced into a 1 liter 3-necked flask equipped with a magnetic stirrer and a condenser. The mixture is heated to 50°-60° C. and 32 g (0.172 mol) of 3,4-dimethoxybenzylchloride are added in a single operation. The reactants are heated to reflux and boiling is maintained for 15 mins; the solution becomes limpid. Thereafter the mixture is cooled and a solution of 27.52 g (0.688 mol) of NaOH in 43 ml of water is introduced dropwise at about 60° C. Heating under reflux is again carried out for 30 minutes, the mixture is cooled and a solution of sodium chloroacetate (obtained by neutralising 22.76 g of chloroacetic acid in 172 ml of water with 20.23 g of NaHCO3) is added dropwise at 60°-70° C. The whole is then heated under reflux for 30 minutes, cooled, filtered and then acidified with 3N HCl. After recrystallisation from toluene, 28.7 g of 3,4-dimethoxybenzylthio-acetic acid are obtained. Yield: 69%. Instantaneous melting point: 94° C.
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