Chemical Reactions

Lucas reagent is a solution of saturated and anhydrous zinc chloride in concentrated hydrochloric acid. This solution is used to classify alcohols of low molecular weight. The reaction is a substitution in which the chloride replaces a hydroxyl group.

(i) This reaction occurs between an aromatic aldehyde and an aliphatic anhydride having at least two atoms.

(ii) Electron attracting groups attached to the ring increases the efficiency of Perkin condensation while electron releasing groups (electron donating group) decreases the efficiency of Perkin's reaction.

Hence

be the most reactive towards perkin's condensation.

HCHO contain no -H in its structure. Thus in presence of NaOH it show Cannizaro reaction.

Both aldehydes and ketone reacts with to form yellow, orange or red . of -dinitrophenylhydrazones.

with Fehling solution, Shiff??s reagent and Tollen reagent only aldehyde reacts. These are distinguishing test for aldehyde and ketones.

Cannizzaro reaction

Aldehydes that do not contain an -hydrogen atom, when treated with conc. NaOH solution undergo disproportionation, i.e. self reduction oxidation. As a result, one molecule of the aldehyde is reduced to corresponding alcohol and the other is oxidised to corresponding carboxylic acid.This is known as Cannizzaro reaction.

The reaction of p-methyl benzaldehyde and is an example of Cannizzaro reaction..