Carboxylic acids, from primary nitroalkanes

When equal amount of concentrated mineral acid and primary nitroalkane react, a carboxylic acid and a hydroxylamine salt are generated, generally with yield of up to 85-90 %. When sulfuric acid reacts with nitromethane [6], products are CO and hydroxylamine sulfate. The mixture from the reaction between anhydride sulfuric acid and a primary nitroalkane at 60 °C was poured into ice-water and then... 

The a-hydrogens of nitroalkanes are appreciably acidic due to resonance stabilization of the anion [CH3NO2, 10.2 CH3CH2NO2, 8.5]. The anions derived from nitroalkanes give typical nucleophilic addition reactions with aldehydes (the Henry-Nef tandem reaction). Note that the nitro group can be changed directly to a carbonyl group via the Nef reaction (acidic conditions). Under basic conditions, salts of secondary nitro compounds are converted into ketones by the pyridine-HMPA complex of molybdenum (VI) peroxide. Nitronates from primary nitro compounds yield carboxylic acids since the initially formed aldehyde is rapidly oxidized under the reaction conditions. 

---