Reactions · Henry 1895 ↗
Henry reaction (nitroaldol addition)
Overview
RCH₂NO₂ + R'CHO → R'CH(OH)CH(NO₂)R
Base-catalysed addition of a nitroalkane to an aldehyde to give a β-nitro alcohol that dehydrates under Knoevenagel-Henry conditions to the conjugated nitroalkene. Default example here is the textbook β-nitrostyrene prep — yellow needles, mp 58 °C, recrystallised from EtOH.
Conditions: Knoevenagel-Henry variant: glacial acetic acid (or 80 % aq. AcOH for milder conditions) with 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 nitrostyrene, recrystallise from boiling EtOH. Slow cooling gives larger needles; seeding the cooling solution with a previously-isolated crystal accelerates onset. Classical alternative (Worrall, Org. Synth. Coll. Vol. 1, 413): NaOH in MeOH at 0–5 °C — fast (≤1 h to first crop) but lower yield (~50 %).
- Expected yield
- 70–80 %
- Expected duration
- 5–14 days at RT in the dark; 3–6 h at reflux (Knoevenagel variant)
Reagents
| Reagent | Role | Equiv | MW | ρ |
|---|---|---|---|---|
|
Benzaldehyde
100-52-7 · C7H6O
Aldehyde acceptor. |
reactant | 1.0 | 106.12 | 1.050 |
|
Nitromethane
SDS
75-52-5 · CH3NO2
Nitroalkane — limiting reagent in this template. |
reactant | 1.0 | 61.04 | 1.130 |
|
109-73-9
109-73-9 · C4H11N
Primary amine catalyst — typically 5–20 mol%. |
catalyst | 0.1 | 73.14 | 0.730 |
|
Acetic Acid
64-19-7 · C2H4O2
Glacial acetic acid — proton shuttle + Mannich buffer. |
solvent | — | 60.05 | 1.040 |
|
Β-Nitrostyrene
102-96-5 · C8H7NO2
(E)-β-Nitrostyrene. Yellow crystalline needles, mp 58 °C; recrystallises cleanly from boiling EtOH or MeOH. The parent Knoevenagel-Henry condensation product — Worrall's Org. Synth. 1929 prep is the classical undergraduate preparation of this compound. |
product | 1.0 | 149.15 | — |
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