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Reaction Scale Calculator

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Cannizzaro disproportionation: 2 benzaldehyde → benzyl alcohol + sodium benzoate

2 Ph–CHO + NaOH → Ph–CH2–OH + Ph–COO⁻ Na⁺

Textbook redox disproportionation of an α-H-free aldehyde. Concentrated NaOH drives hydride transfer between two benzaldehyde molecules: one is reduced to benzyl alcohol, the other oxidised to sodium benzoate. Mechanism goes through a tetrahedral hydride-donor intermediate; chemists isolate the products by acidifying the aqueous phase to precipitate benzoic acid and ether-extracting the alcohol.

Conditions: Dissolve NaOH (1.1 equiv per pair of aldehyde, ~50 wt% aq.) in water. Add benzaldehyde (2.0 equiv) — exotherm; cool with an ice bath to keep T < 30 °C during addition. Stir vigorously (the system rapidly thickens to a paste as the disproportionation advances). Continue stirring 4–24 h at RT until a single phase forms. Workup — Dilute with cold water; extract benzyl alcohol into Et2O (3×). Acidify the aqueous phase with conc. HCl to pH < 2 — benzoic acid precipitates as white needles. Filter, wash with cold water, dry. Recrystallise from hot water. α-H-free aldehydes are the substrate scope (benzaldehyde, furfural, formaldehyde): if the aldehyde has α-H, aldol condensation outcompetes Cannizzaro at the same conditions.

Expected yield
70–88 %
Expected duration
4–24 h at RT after 0–30 °C base addition

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