How to Prepare Benzaldehyde
Toluene: benzaldehyde is obtained from oxidation of toluene by chromyl chloride CrO2Cl2. This reaction is called Etard’s Reaction.
C6H5CH3 + 2CrO2Cl2 → C6H5CH(OCrOHCl2)2 → C6H5CHO
Benzaldehyde is also obtained by oxidation of acidic solution of toluene’s manganese dioxide MnO₂. In the presence of vanadium pentoxide(V₂O₅) at 350°C, oxidation of toluene by air oxygen also yields benzaldehyde.
Benzenal chloride: benzenal chloride (C7H7Cl) gets benzaldehyde on heating with lead nitrate solution in the atmosphere of carbon dioxide gas.
2C6H5CH2Cl + Pb(NO3)2 → 2C6H5CHO + PbCl2 + 2HNO2
Preparation Method
To make benzaldehyde in the laboratory, take 10 grams of benzene chloride, 8 gram lead nitrate and about 50 ml of water in a round flask. Attaches a reflux condenser to the flask. CO2 gas flows into the flask. So that the atmosphere of CO2 remains in the flask.
Heats the flask for about 6 hours in this condition. The mixture is then cooled and extracted by ether. Benzaldehyde enters the ether layer. Separating the ether layer and adding a saturated solution of sodium bisulfite(NaHSO3) to it.
Crystals of benzaldehyde sodium bisulfite are obtained. They are filtered and dried. Benzaldehyde is released upon heating these crystals with sulfuric acid. It is extracted by ether. Distill the ether solution and separate the ether. After benign distillation of the remaining fluid, pure benzaldehyde is obtained at 179°C.
Benzal chloride: Benzaldehyde is obtained by reaction of benzal chloride with aqueous NaOH or KOH. C7H6Cl2
C6H5CHCl2 → C6H5CH(OH)2 → C6H5CHO
Benzene alcohol: benzaldehyde can be obtained by oxidation of benzene alcohol by acidic potassium dichromate.
C6H5CH2OH + O → C6H5CHO + H2O
Benzaldehyde is also obtained when the vapors of benzene alcohol are precipitated at 300°C heated copper.
Benzoyl chloride: benzaldehyde is obtained from rosenmund reduction of Benzoyl chloride.
C6H5COCl + H2 → C6H5CHO + HCl
Benzene: benzaldehyde is also obtained from benzene by gattermann koch aldehyde synthesis.
C6H6 + CO → C6H5CHO + HCl
