Question

a) The product obtained when benzene is treated with carbon monoxide and hydrogen chloride in presence of anhydrous AICI₃ is

i) Chlorobenzene 

ii) Phenol 

iii) Benzaldehyde 

iv) Benzoic acid 

b) How will you carry out the following conversions?

OR
Explain the following:

i) Esterification

ii) Tollen’s test

iii) HVZ reaction

iv) Decarboxylation of Carboxylic acid.

Answer 1

a) iii) Benzaldehyde

b) i) Toluene on heating with alkaline KMnO₄ followed by acid hydrolysis give benzoic acid.

ii) Benzoic acid reacts with ammonia to give ammonium benzoate which on further heating at high temperature gives benzamide.

iii) Propanoic acid on reduction using LiAIH₄ gives Propan-1 -al.

iv) Ethanoic acid on heating with mineral acids such as H₂SO₄ or with P₂O₅ gives ethanoic anhydride.

i) Estenfication: Carboxylic acids are estenfied with alcohols or phenols in the presence of a mineral acid such as concentrated H₂SO₄ or HCI gas as a catalyst.

ii) Tollens’s Test: On warming an aldehyde with freshly prepared ammoniacal silver nitrate solution (Tollens’ reagent), a bright silver minor is produced due to formation of silver metal. The aldehydes are oxidised to corresponding carboxylate anion.

Ketones will not give this reaction because Tollens’ reagent being a mild oxidising agent cannot oxidise ketones.

iii) HVZ reaction: Carboxylic acids having an α – hydrogen are halogenated at the α – position on treatment with chlorine or bromine in the presence of small amount of red phosphorus to give halocarboxylic acids. The reaction is known as Hell-Volharti-Zelinsky (HVZ) reaction.

iv) Decarboxylation: Carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with sodalime (NaOH and CaÇ. in the ratio of 3: 1). The reaction is kriownas decar carboxylation.