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Henry reaction (nitroaldol addition)
RCH₂NO₂ + R'CHO → R'CH(OH)CH(NO₂)R
Base-catalysed addition of a nitroalkane to an aldehyde or ketone to give a β-nitro alcohol. Key C-C bond-forming step in the Knoevenagel-Henry route to β-nitrostyrenes (e.g. P2NP).
Conditions: Glacial acetic acid (or 80 % aq. AcOH for milder conditions); primary amine catalyst (n-butylamine, 5–20 mol%). Run at 20–25 °C in the dark for the slow variant, or at reflux (~118 °C glacial) for the faster Knoevenagel variant. Workup: pour onto cold water, filter the yellow nitroalkene, recrystallise from MeOH or EtOH.
- Expected yield
- 60–75 %
- Expected duration
- 5–14 days at RT in the dark; 3–6 h at reflux (Knoevenagel variant)