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 $C{H}_{3}COOH$
• 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. $C{H}_{3}COOH$ has three $\alpha$ -H-atoms but formic acid does not have $\alpha$ -H-atom hence formic acid cannot be halogenated.
For e.g. ${\text{CH}}_{\text{3}}\text{COOH}\text{+}{\text{Cl}}_{\text{2}}{\to }_{{\text{P}}_{\text{4}}}^{\text{Δ}}{\text{ClCH}}_{\text{2}}\text{COOH}\text{+}\text{HCl}$