3 - methyl - 2 - butanone cannot be removed from 3 - methyl - 2 - butanone and formic acid mixtures by distillation because of the presence of the maximum azeotrope between 3 - methyl - 2 - butanone and formic acid . 3 - methyl - 2 - butanone can be readily removed from 3 - methyl - 2 - butanone - formic acid mixtures by extractive distillation in which the extractive agent is dimethylacetamide , dimethylformamide or these with certain high boiling organic compounds .