[CH3:1][C:2]1[NH:6][C:5]2[CH:7]=[CH:8][CH:9]=[C:10]([CH2:11][OH:12])[C:4]=2[N:3]=1>[O-2].[Mn+4].[O-2].C(OCC)(=O)C>[CH3:1][C:2]1[NH:6][C:5]2[CH:7]=[CH:8][CH:9]=[C:10]([CH:11]=[O:12])[C:4]=2[N:3]=1(a-3) A mixture of 10 parts of 2-methyl-1H-benzimidazole-4-methanol, 10 parts of manganese(IV) oxide and 180 parts of ethyl acetate was stirred for 19 hours at room temperature. The reaction mixture was filtered over diatomaceous earth and washed with a mixture of ethyl acetate and methanol (80:20 by volume). The filtrate was evaporated and the residue was crystallized from 2-butanone. The product was filtered off and dried, yielding 3.5 parts (35.2%) of 2-methyl-1H-benzimidazole-4-carboxaldehyde (int. 67).
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