The correct answer is Option (4) → $α$-halocarboxylic acids
- Option 1: Alcohols Alcohols are typically formed by hydration of alkenes, reduction of carbonyl compounds, or substitution reactions of alkyl halides. The HVZ reaction does not involve formation of an –OH group, so alcohols are not the products. The reagents in HVZ (halogen and red phosphorus) specifically promote α-halogenation of carboxylic acids, not alcohol formation.
- Option 2: Aldehydes Aldehydes are generally produced by oxidation of primary alcohols, ozonolysis of alkenes, or reduction of acid derivatives. The HVZ reaction does not change the carboxyl group (–COOH) into an aldehyde. Instead, it substitutes a hydrogen atom at the α-carbon of a carboxylic acid with a halogen.
- Option 3: Ketones Ketones are formed by oxidation of secondary alcohols or Friedel–Crafts acylation reactions. The HVZ reaction does not introduce a carbonyl group nor does it modify the existing carbonyl group into a ketone. Its function is specifically α-halogenation adjacent to the carboxylic acid group.
- Option 4: α-Halocarboxylic acids This is correct. The HVZ reaction involves treatment of a carboxylic acid with halogen (Cl₂ or Br₂) in the presence of red phosphorus, leading to substitution of a hydrogen atom at the α-carbon by a halogen. Thus, the product is an α-halogenated carboxylic acid.
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