Question

Acetic acid can be halogenated in presence of phosphorus and chlorine. Formic acid cannot be halogenated with same way because of

• A. presence of $\alpha $ -H-atom in formic acid
• B. absence of $\alpha $ -H-atom in formic acid
• C. absence of $\alpha $ -H-atom in $CH_{3}COOH$
• D. higher acidic strength of acetic acid than formic acid

Answer 1

Answer: (B)

HVZ reaction is given by only those carboxylic acids which have $\alpha $ -H-atom. $CH_{3}COOH$ has three $\alpha $ -H-atoms but formic acid does not have $\alpha $ -H-atom hence formic acid cannot be halogenated.
For e.g. $\text{CH}_{\text{3}} \text{COOH} \, \text{+} \, \text{Cl}_{\text{2}} \rightarrow _{\text{P}_{\text{4}}}^{\text{Δ}} \text{ClCH}_{\text{2}} \text{COOH} \, \text{+} \, \text{HCl}$