Claisen-Schmidt aldol: benzaldehyde + acetone → benzalacetone

Reagent table at any scale. Enter how much benzaldehyde you have, or pick another reagent, and every mass, volume and amount follows.

Conditions and workup
OBenzaldehyde+OAcetoneNaOH (20 mol%)EtOHO4-Phenyl-3-buten-2-one70–85 %
OBenzaldehyde+OAcetoneNaOH (20 mol%)EtOHO4-Phenyl-3-buten-2-one70–85 %

Reagent table

ReagentRoleEquivMW (g/mol)ρ (g/mL)nmV
Benzaldehyde100-52-7limitingyour amount reactant 106.12 1.050 94.2 mmol 10.0 g 9.52 mL
Acetone67-64-1 reactant 58.08 0.790 471 mmol 27.4 g 34.6 mL
Sodium hydroxide1310-73-2 catalyst20 mol% 40.00 — 18.8 mmol 754 mg —
Ethanol64-17-5 solvent — 46.07 0.790 — — 286 mL
4-Phenyl-3-buten-2-one122-57-6 product — 146.19 — 94.2 mmol 13.8 g —
Theoretical yield13.8 g94.2 mmol of 4-phenyl-3-buten-2-one
Expected at 70–85 %9.64 g – 11.7 gtypical isolated yield
Solvent286 mLEthanol, 0.33 M
Limiting reagentBenzaldehyde
Notes on the reagents
Benzaldehyde
Benzaldehyde — limiting reagent. Freshly distilled or wash with 5 % NaHCO3 then water to remove benzoic acid (white film indicates oxidation).
Acetone
Acetone — large excess (5 equiv) to suppress double-condensation to dibenzylideneacetone (DBA). Also serves as a co-solvent.
Sodium hydroxide
Sodium hydroxide — catalytic base; deprotonates acetone's α-carbon. Aqueous, dissolved into the EtOH/H2O reaction medium.
Ethanol
Ethanol (95 % aqueous) — primary reaction medium. The 5 % water is part of the kinetic control: anhydrous EtOH overpowers the elimination step.
4-Phenyl-3-buten-2-one
Benzalacetone (4-phenyl-3-buten-2-one, E-isomer) — pale-yellow needles; mp 41–42 °C; recrystallises from EtOH; mild floral odour. Skin sensitiser — gloves.
How the amounts are calculated

The amount you enter is converted to millimoles with the molar mass, or with density and molar mass for a volume. Dividing by its equivalents gives the millimoles per equivalent; every other reagent is that times its own equivalents. Masses use the molar mass of the structure. Volumes are given for compounds that are liquid at room temperature and have a density on file. A reagent sold as a solution, such as n-BuLi in hexanes, gets the volume of that solution; enter your bottle's titre and every volume follows.

The theoretical yield assumes full conversion of the limiting reagent: the reactant with the fewest millimoles per stoichiometric coefficient. Change an equivalent and the limiting reagent may change with it.

Solvent volume and concentration

The concentration refers to the substrate, the limiting reagent: solvent volume = millimoles of substrate ÷ concentration, since 1 M is 1 mmol/mL. Liquid reagents add to the final volume, so the real concentration ends up slightly lower. Leave the field empty to leave the solvent out.

What the table cannot know

Purity, water content and reagents sold as solutions. Grignard reagents and organolithiums are bought as solutions: take the millimoles from the table and divide by the molarity on the bottle to get the volume to syringe out.

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