Question

Conversion of phenol to benzaldehyde

Answer 1

To phenol, add zinc dust. ... Treatphenol with zinc dust to obtain benzene. Use friedel crafts alkylation method to add a methyl group to the ring. Oxidise the methyl group with chromyl chloride (Etard reaction) to get the required benzaldehyde.

Answer 2

Conversion of phenol to benzaldehyde following method

METHOD -I

Step 1. Phenol on treatment with chloroform and KOH (Reimer-Tiemann reaction) yields salicylaldehyde, C6H4(CHO)(OH).

STEP 2. Salicylaldehyde on distillation with zinc dust will form benzaldehyde.

C6H4(CHO)(OH) + Zn = C6H5CHO + ZnO

METHOD-II

Step 1. Phenol on distillation with zinc dust is reduced to benzene.

C6H5OH +Zn = C6H6 + ZnO

STEP 2. Benzene undergoes Friedel-Crafts reaction with CH3Cl to give toluene.

C6H6 + CH3Cl = C6H5CH3 + HCl

STEP 3. Toluene can be oxidised to benzaldehyde by reacting it with chromyl chloride, CrO2Cl2 (Etard's reaction).

Explanation:

1.The Reimer–Tiemann reaction is a chemical reaction used for the ortho-formylation of phenols; with the simplest example being the conversion of phenol to salicylaldehyde. The reaction was discovered by Karl Reimer and Ferdinand Tiemann.

2.The Etard reaction is a chemical reaction that involves the direct oxidation of an aromatic or heterocyclic bound methyl group to an aldehyde using chromyl chloride.