Preparation of 2,4 Dinitro-phenyl hydrazone (2,4-DNP) derivatives of aldehydes R-CHO / ketones R-Co-R

Abstract

An alternative variation of the most common preparation of 2,4-dinitrophenylhydrazine reagent is presented. This method is suitable for scaling up for quantities required for preparing stock reagent for classes. Since the action of 2, 4-dinitrophenylhydrazine (Brady’s reagent) on aldehydes and ketones was first investigated by Purgotti in 1894, its usefulness as an analytical reagent for carbonyl containing compounds has been thoroughly exploited. The 2, 4 -DNHP reagent is an orange crystalline solid melting at 1990C. Its usefulness as a reagent stems from the fact that it forms crystalline derivatives which are easily purified and have melting points supposedly characteristic of the aldehyde or ketone used in preparing the derivative. In principle, each aldehyde and ketone should form a single 2,4-dinitrophenylhydrazone (DNPH) with a characteristic melting point. In practice, however, a number of the aldehydes and ketones do not follow this general rule but form multiple derivatives, differing either in melting point, crystal structure, or both. Even the colors of pure DNPH's of a particular aldehyde or ketone are sometimes different.