Grignard addition: phenylmagnesium bromide + benzaldehyde → diphenylmethanol
Ready to scaleOrganometallic addition
Textbook Grignard addition. Phenylmagnesium bromide (PhMgBr) attacks benzaldehyde's carbonyl carbon; aqueous acidic workup releases diphenylmethanol (benzhydrol). PhMgBr is bought as a 1 M or 3 M solution in anhydrous Et2O or THF — solid Grignards are not weighed. Reaction is run under N2 with rigorous water exclusion.
Conditions
Cool a flame-dried, N2-flushed flask to 0 °C. Charge anhydrous Et2O (~3 mL per mmol of benzaldehyde). Add benzaldehyde (1.0 equiv) by syringe; stir 5 min. Add PhMgBr (1.1 equiv, 1 M or 3 M solution in Et2O) dropwise over 10 min — exotherm; control addition rate to keep T < 5 °C. Warm to RT, stir 1–2 h.
Workup
Quench cautiously with sat. NH4Cl (or 10 % HCl); extract with Et2O; wash organic with sat. NaHCO3 + brine; dry MgSO4. Concentrate. Recrystallise from hexane or hexane/EtOAc. White crystals; mp 65–67 °C.
| Compound | Role | Equiv | MW (g/mol) | ρ (g/mL) | Safety |
|---|---|---|---|---|---|
| Benzaldehyde100-52-7 · C7H6OBenzaldehyde — limiting reagent. Freshly distilled or wash with 5 % NaHCO3 then water to remove benzoic acid (white film on the bottle indicates oxidation). Anhydrous before use — Grignards quench instantly on water. | reactant | 1.0 | 106.12 | 1.050 | WarningSDS |
| Phenylmagnesium bromide100-58-3 · C6H5BrMgPhenylmagnesium bromide — purchased as 1 M or 3 M solution in anhydrous Et2O or THF; never weighed as a solid. Slight excess (1.1 equiv) compensates for trace H2O in the substrate or solvent that consumes the Grignard. | reactant | 1.1 | 181.31 | — | — |
| Diethyl ether60-29-7 · C4H10ODiethyl ether — anhydrous, sodium-dried. THF (CAS 109-99-9) is the modern alternative for less reactive Grignards but Et2O remains the textbook choice for PhMgBr addition to aromatic aldehydes. | solvent | — | 74.12 | 0.710 | DangerSDS |
| Diphenylmethanol91-01-0 · C13H12ODiphenylmethanol (benzhydrol) — white crystalline solid, mp 65–67 °C; recrystallises from hexane. Mild aromatic odour. Used as a starting material for benzhydrol-derived pharmaceuticals (diphenhydramine, etc.). | product | — | 184.24 | — | Warning |