[CH2:1]([O:8][C:9]1[C:16]([O:17][CH2:18][C:19]2[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=2)=[CH:15][CH:14]=[CH:13][C:10]=1[CH:11]=[O:12])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.[O-:25][Mn](=O)(=O)=O.[K+].C(=O)C1C=CC=CC=1>CC(C)=O.O>[CH2:1]([O:8][C:9]1[C:16]([O:17][CH2:18][C:19]2[CH:24]=[CH:23][CH:22]=[CH:21][CH:20]=2)=[CH:15][CH:14]=[CH:13][C:10]=1[C:11]([OH:25])=[O:12])[C:2]1[CH:3]=[CH:4][CH:5]=[CH:6][CH:7]=119.8 g of 2,3-dibenzyloxybenzaldehyde are dissolved in 100 ml of acetone. While stirring vigorously and heating at 40° C., a solution of 4.0 g of KMnO4 in 90 ml of H2O is added within 45 min, the precipitated benzaldehyde being redissolved by the addition of a total of 150 ml of acetone. Once addition of the KMnO4 solution is complete, the mixture is boiled under reflux for one hour. The hot solution is then filtered, and the precipitate is washed with hot water. The carboxylic acid crystallizes out in fine white needles on acidification of the cold aqueous solution with dilute HCl. 18.0 g of the desired compound are obtained (92% yield). MS: 334 (M+); M.p.: 185°-187° C.
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