The unsaturated ether on acidic hydrolysis produces carbonyl compounds as shown below:- CH _ 3 - CH = CH - O - CH = CH _ 2$$ \mathrm{CH} _ {3} - \mathrm{CH} = \mathrm{CH} - \mathrm{O} - \mathrm{CH} = \mathrm{CH} _ {2} $$ H _ 3 O ^ (+)$$ \downarrow \mathrm{H} _ {3} \mathrm{O} ^ {(+)} $$ CH _ 3 - CH _ 2 - CH = O and O = CH - CH _ 3$$ \mathrm{CH} _ {3} - \mathrm{CH} _ {2} - \mathrm{CH} = \mathrm{O} \text{ and } \mathrm{O} = \mathrm{CH} - \mathrm{CH} _ {3} $$ Based on this, predict the solution / reagent that will help to distinguish "P" and "Q" obtained in the following reaction.

Core Logic

The given reactant is p-hydroxybenzaldehyde, which contains both a phenolic -OH$-OH$ group (acidic) and an aldehyde group (electrophilic).

When one equivalent of Grignard reagent (PhMgBr$PhMgBr$) is added, it behaves primarily as a strong base due to the presence of an acidic proton. Acid-base reactions are extremely fast compared to nucleophilic additions.

The acidic phenolic -OH$-OH$ reacts with PhMgBr$PhMgBr$:

Upon workup with aq. NH₄Cl$aq. NH_4Cl$, the phenoxide ion simply regenerates the starting p-hydroxybenzaldehyde. However, the question asks for the number of hydroxyl groups present in the formed product (Benzene).

The distinct product formed in the reaction is Benzene. Benzene has 0 hydroxyl groups.

Pattern Recognition

Whenever a Grignard reagent encounters a molecule with an acidic hydrogen (alcohol, phenol, amine, alkyne), it will invariably act as a base first. If only 1 equivalent is used, nucleophilic addition to carbonyls will NOT happen.

Chapter Mix

Class 12 Chemistry: Aldehydes, Ketones and Carboxylic Acids Class 12 Chemistry: Alcohols, Phenols and Ethers