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

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.

Preparation of benzaldehyde from toluene

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

Properties of benzaldelyde

Aromatic aldehydes and ketones undergo electrophilic substitution at the ring in which the carbonyl group acts as a deactivating and meta-directing group.

Important reactions of benzaldelyde

Perkin condensation

Benzoin condensation

Electrophilic substitution reaction

Aromatic aldehydes and ketones undergo electrophilic substitution at the ring in which the carbonyl group acts as a deactivating and meta-directing group.

Cannizzaro's reaction

Aldehydes which do not have an a-hydrogen atom undergo self oxidation and reduction (i.e., disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol and another is oxidised to carboxylic acid salt.

Aldehydes containing a-hydrogen atoms when heated with concentrated alkali give brown resinous mass.