Reactivity of 5-nitro-2-furaldehyde in alkaline and acidic solutions.

5-Nitro-2-furaldehyde (NFA) forms in alkaline solutions an anion of nitronic acid of (5-nitro-furan-2-yl)-methanediol. Upon acidification (5-nitro-furan-2-yl)-methanediol (HNFA) appears with pKa=4.6. Then, in a novel irreversible redox ring-opening reaction, nitrile oxide of alpha-ketoglutaconic acid is formed which hydrolyses in acidic solutions. With increasing pH it dimerizes to furoxane or polymerizes to hydraxamates. Some of the products were separated and identified by IR and NMR spectroscopy, confirmed by elemental analysis.