[C:1]([OH:22])(=[O:21])[CH2:2][CH2:3][CH2:4][CH2:5][CH2:6][CH2:7][CH2:8][CH2:9][CH2:10][CH2:11][CH2:12][CH2:13][CH2:14][CH2:15][CH2:16][CH2:17][C:18]([OH:20])=[O:19].O.[C:24]1([CH3:34])[CH:29]=[CH:28][C:27](S(O)(=O)=O)=[CH:26][CH:25]=1.C(O)C1C=CC=CC=1>C1(C)C=CC=CC=1>[CH2:34]([O:19][C:18](=[O:20])[CH2:17][CH2:16][CH2:15][CH2:14][CH2:13][CH2:12][CH2:11][CH2:10][CH2:9][CH2:8][CH2:7][CH2:6][CH2:5][CH2:4][CH2:3][CH2:2][C:1]([OH:22])=[O:21])[C:24]1[CH:29]=[CH:28][CH:27]=[CH:26][CH:25]=1A solution of 1,18-octadecanedioic acid (75 g, 0.24 mol), p-toluene sulfonic acid mono hydrate (2.27 g, 11.9 mmol) and benzyl alcohol (20.7 g, 0.19 mol) in toluene (2.75 L) was heated to reflux for 3 hr. Water was removed by azeotropic distillation during reflux. Celite (25 g) was added and the mixture was cooled to 40° C. and stirred for an additional hour. The mixture was purified by plug filtration through silica using toluene as mobile phase. Fractions containing 1,18-octadecanedioic acid mono benzyl ester was collected and the volume was reduced by vacuum distillation at 75° C. The solution was cooled to 50° C., heptane was added, and the mixture was cooled to 35° C. Upon crystallisation additional heptane was added over a period of 15 min. and finally the mixture was cooled to 10° C. for an additional hour. The product was collected by filtration, washed with heptane and dried in vacuum. Yield of 1,18-octadecanedioic acid mono benzyl ester was 34 g (35%).
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