C1(SC2C=CC=C[C:9]=2[C:10](O)=[O:11])C=CC=CC=1.[OH-:17].[K+].[C:19]([OH:26])(=[O:25])/[CH:20]=[CH:21]\[C:22]([OH:24])=[O:23]>O.C(O)C>[CH2:10]([OH:11])[CH2:9][O:23][C:22]([CH2:21][CH:20]([OH:17])[C:19]([OH:26])=[O:25])=[O:24]A mixture of methyl 2-(4-(2-chloroethoxy)phenylsulfanyl)benzoate (7.2 g, 22.0 mmol), 1-(4-chlorobenzyl)piperazine (4.6 g, 22.0 mmol), anhydrous potassium carbonate (10.5 g), potassium iodide (0.2 g) and 4-methylpentane-2-one (120 ml) was refluxed for 20 h (the reaction was monitored by TLC and continued till 1-(4-chlorobenzyl)piperazine was not present in the reaction mixture). The hot mixture was filtered, the filtrate was evaporated to dryness. The residue was purified by column chromatography on silica gel using dichloromethane and chloroform as eluents. Crystallization from a mixture of n-hexane-ether (1:1) provided methyl ester of the title acid (4.2 g, 38.5%), m.p. 106-108° C. For C27H29ClN2O3S (497.1) calculated: 65.24% C, 5.88% H, 7.13% Cl, 5.64% N, 6.45% S; found: 65.62% C, 6.19% H, 7.08% Cl, 5.20% N, 6.35% S. 1H NMR spectrum (CDCl3): CH3(ester) 3.96 s; aromatic H on the phenylsulfanylbenzoic acid moiety: H(6) 8.00 dd (J=2.0, 7.5 Hz); H(3,4,5,3′,5′) 6.68-7.20 m; aromatic H of 4-chlorobenzyl group 7.28 s. A solution of potassium hydroxide (1.7 g) in water (10 ml) was added to a stirred solution of this ester (3.7 g, 7.4 mmol) in ethanol (40 ml) and the mixture was refluxed for 1 h. The residue after evaporation was dissolved in water and acidified with acetic acid, the mixture was cooled down and the formed precipitate was extracted with chloroform. The extract was dried with sodium sulfate, the residue after evaporation was suspended in ethanol (50 ml) and a solution of maleic acid (1.2 g, 10.0 mmol) in ethanol (10 ml) was added and the mixture was stirred for 8 h at 20° C. The insoluble portion was filtered off, washed with ethanol to provide the title hydrogenmaleate (4.0 g, 90.2%), m.p. 194-196 ° C. For C26H27ClN2O3S. C4H4O4 (599.1) calculated: 60.14% C, 5.22% H, 5.92% Cl, 4.68% N, 5.35% S; found: 59.94% C, 5.31% H, 6.01% Cl, 4.51% N,5.26% S.
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