N-methyl-4-hydrazino-7-nitrobenzofurazan as a new reagent for air monitoring of aldehydes and ketones

The synthesis of N-methyl-4-hydrazino-7-nitrobenzofurazan (MNBDH) and its application as a new reagent for the determination of aldehydes and ketones are described. MNBDH reacts with carbonyl compounds in acidic media to the corresponding MNBD-hydrazones. In contrast to the established reagent 2,4-dinitrophenylhydrazine (DNPH), MNBDH is oxidized by both ozone and nitrogen dioxide quantitatively to only one product, N-methyl-4-amino-7-nitrobenzofurazan (MNBDA). This can easily be separated from the hydrazones of lower aldehydes by means of HPLC. Due to larger molar absorptivities and absorption maxima at wavelengths over 470 nm, selectivity is higher and limits of detection are lower for the new reagent compared to DNPH. MNBDH reacts slightly faster than DNPH with carbonyl compounds and significantly faster than other N-alkylated hydrazine reagents.