Cannizzaro disproportionation: 2 benzaldehyde → benzyl alcohol + sodium benzoate
Reagent table at any scale. Enter how much benzaldehyde you have, or pick another reagent, and every mass, volume and amount follows.
Notes on the reagents
- Benzaldehyde
- Benzaldehyde — both reductant AND oxidant (the same molecule plays both roles in the disproportionation). Freshly distilled; remove benzoic acid (white film on bottle) by 5% NaHCO3 wash before use.
- Sodium hydroxide
- Sodium hydroxide — slight excess (1.1 eq per aldehyde pair) so the reaction goes to completion. Used as 50 wt% aqueous solution (~19 M); concentrated NaOH is corrosive — face shield + chemical-resistant gloves.
- Water
- Water — co-solvent / reaction medium. The alkali drives the hydride transfer; water solvates the resulting alkoxide. Dilution kills the rate (Cannizzaro is third-order in [base]).
- Benzoic acid
- Benzoic acid — the oxidation product; mp 122 °C. Released by acidifying the aqueous phase with conc. HCl. White needles from hot water recrystallisation.
- Benzyl alcohol
- Benzyl alcohol — the reduction product; bp 205 °C. Extract into Et2O after dilution; clean by distillation.
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.