Conventional methods for forming 2, 4-dinitrophenylhydrazones (2, 4-DNPH's) usually leave traces of acids complexed with the derivatives and cause variable melting points. A bicarbonate wash of the 2, 4-DNPH crystals removes the acid and reproducibly gives derivatives with previously reported or higher melting ranges. 2, 4-DMH's of hydroxy ketones previously unattainable by the standard methods were prepared by this method. NMR ...
