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

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.

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.

chlorination of toluene to benzylidene chloride

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.

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