Preparation of benzaldelyde from toluene

Benzaldehyde is the simplest aromatic aldehyde. It occurs in bitter almonds in the form of its glucoside,amygdalin ( C₂₀H₂₇O₁₁N) . When amygdalin is boiled with dilute acids, it hydrolyses into benzaldehyde, glucose and HCN

CN

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C₆H₅ CHOC₁₂ H₂₁ O₁₀ + 2H₂O ———→ C₆H₅ CHO + 2C₆ H₁₂ O₆ + HCN

Amygdalin Benzaldehy de Glucose

Benzaldehyde is also known as oil of bitter almonds.

Laboratory Method of preparation of Benzaldehyde

It is conveniently prepared by boiling benzyl chloride with copper nitrate or lead nitrate solution in a current of carbon dioxide.

Heat

C₆H₅ CH₂ Cl + Cu( NO₃ )₂ ———→ 2C₆H₅ CHO + CuCl₂ + 2HNO₂

Benzyl chloride or CO₂ Benzaldehy de

Pb(NO₃ )₂

[ 2HNO₂ ———→ NO + NO₂ + H₂O ]

Preparation of benzaldehyde from toluene

Benzaldehyde is prepared by side chain chlorination of toluene to benzylidene chloride followed by hydrolysis.

Benzaldehyde is a colorless liquid (boiling point 452 K) with the smell of bitter almonds. It is used in perfurmery and dye industry for making dyes like malchite green.