C([C:4]1[C:5]([C:24]([O-:26])=[O:25])=[C:6](C(C)C)[C:7]([S:13][CH2:14][C:15]2[CH:20]=[CH:19][CH:18]=[CH:17][CH:16]=2)=[C:8]([CH:12]=1)[C:9]([O-:11])=[O:10])(C)C.CO.[OH-].[K+]>O>[CH2:14]([S:13][C:7]1[CH:6]=[C:5]([C:24]([OH:26])=[O:25])[CH:4]=[CH:12][C:8]=1[C:9]([OH:11])=[O:10])[C:15]1[CH:16]=[CH:17][CH:18]=[CH:19][CH:20]=1The diisopropyl-(benzylthio)-terephthalate obtained in Preparation 2 is refluxed with 500 ml. of methanol, 25 g. of potassium hydroxide and 50 ml. of water for 2 hours. The reaction mixture is then concentrated to a small volume, cooled, diluted with water and filtered through diatomaceous earth (Celite). The thus-obtained filtrate is acidified with 4N hydrochloric acid and the precipitate with forms is collected by filtraton and dried in an oven at 90°-100° C. to yield 45 g. (yield 87%) of (benzylthio)-terephthalic acid having a melting point of 299°-300° C.
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