[119-26-6] · C6H6N4O4 · 2,4-Dinitrophenylhydrazine · (MW 198.16)
Alternate Name: DNPH2.
Physical Data: mp 194 °C (198 °C dec).
Solubility: sol DMF, DMSO, aniline, hot EtOAc; mod sol hot EtOH; slightly sol Et2O, CHCl3, benzene, CS2.
Form Supplied in: moist, orange-red solid (contains 20-35% H2O).
Preparative Method: from 2,4-dinitrochlorobenzene and hydrazine in 81-85% yield.7
Handling, Storage, and Precautions: toxic; irritant; flammable solid.
The reaction of 2,4-dinitrophenylhydrazine with aldehydes and ketones represents an extensively studied qualitative test and usually leads to the formation of yellow to orange crystals of the corresponding 2,4-dinitrophenylhydrazone (DNP) derivatives (eq 1).1 Some long-chain aliphatic ketones (e.g. 2-decanone and 6-undecanone) fail to provide solid DNP derivatives.2 Further caution needs to be exercised in interpreting the results since primary and secondary alcohols containing two or more vinyl or aromatic substituents can be oxidized to the carbonyls which then form the corresponding hydrazones in low yields.8 Tertiary alcohols tend to undergo condensation reactions with DNPH2 (eq 2).9
The reactivity of DNPH2 has also been utilized in the syntheses of nitrogen-containing heterocycles.3 Imino ester hydrochlorides, generated from nitriles, react with DNPH2 to provide amidazones, which are converted in situ to 1,3,5-substituted triazoles by reaction with acid chlorides (eq 3).4 Treatment of acyldimedone derivatives with DNPH2 provides indole derivatives (eq 4).5
Catalytic hydrogenolysis of DNP derivatives of alkyl aryl or diaryl ketones leads to the formation of corresponding methylene derivatives and represents a useful alternative to Wolff-Kishner and Clemmenson reductions (eq 5).6 In the steroid series, where ordinary methods fail to induce unsaturation in a-bromo ketones, DNPH2 has been used to effect dehydrohalogenation.10
DNP derivatives can be cleaved to regenerate the carbonyl functionality. Efficient techniques for affecting this transformation include DNP exchange with pyruvate,10a Amberlyst 15 catalyst,11 clay-supported iron(III) nitrate,12 and aqueous titanium(III) ion.13
Humayun S. Ateeq, Fazila Iqbal & Asifa Bano
H. E. J. Research Institute of Chemistry, Karachi, Pakistan