[C:1]([C:4]1[C:5]([OH:25])=[C:6]([CH:22]=[CH:23][CH:24]=1)[NH:7][C:8]([C:10]1[N:14](CC2C=CC=CC=2)[N:13]=[N:12][N:11]=1)=[O:9])(=O)[CH3:2]>C(O)(=O)C.[Pd]>[CH2:1]([C:4]1[C:5]([OH:25])=[C:6]([CH:22]=[CH:23][CH:24]=1)[NH:7][C:8]([C:10]1[NH:14][N:13]=[N:12][N:11]=1)=[O:9])[CH3:2]A solution of 3'-acetyl-1-benzyl-2'-hydroxy-1H-tetrazole-5-carboxanilide (2.6 g) in glacial acetic acid (100 ml) was hydrogenated at 52° C. and 4.1 kg/cm2 for 6 hours, using a catalyst of palladium on charcoal (5% w/w). The mixture was filtered and the filtrate was evaporated in vacuo to give a solid residue, which was recrystallised by dissolving in hot dimethylformamide (7 ml) and slowly adding a large volume of water (100 ml). The colourless solid which crystallised out was collected and discarded as an unwanted by-product. The mother liquor was evaporated under diminished pressure, and the resulting residue was recrystallised from a small volume of aqueous dimethylformamide to give 3'-ethyl-2'-hydroxytetrazole-5-carboxanilide (0.3 g) in the form of pale cream crystals, m.p. 185°-187° C.
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