Question

Phenol can be converted into salicylic acid by:

• A. Cannizaros reaction
• B. Perkins reaction
• C. Tischenko reaction
• D. Reimer-Tiemann reaction

Answer 1

Answer: (D)

[a] Cannizaro reaction: During this reaction aldehydes which do not have a-hydrogen under disproportionation reaction in presence of aq. alkali half of the molecules are oxidised and other half are reduced. $\underset{\text{ formaldehyde }}{\mathrm{HCHO}}+NaOH\to \underset{\text{ sodium formate }}{\mathrm{HCOONa}}+\underset{\text{ methyl alcohol }}{C{H}_{3}OH}$
[b] Perkin condensation: When aromatic aldehydes react with aliphatic acid anhydride in presence of sodium salt of the same acid as base, they form $\alpha ,\beta$-unsaturated acid.
$\underset{\text{benzaldehyde}}{C_6{H}_{5}CHO}+\underset{\text{acetic anhydride}}{(C{H}_{3}CO{)}_{2}O}\stackrel{\mathrm{CH}{}_3\mathrm{COONa}}{\to }$
$\underset{\text{cinnamic acid}}{C_6{H}_{5}CH=CHCOOH}+C{H}_{3}COOH$
[c] Tischenko reaction: All the aldehydes on reaction with aluminium ethoxide form esters.
$\underset{\text{propanaldehyde}}{2C{H}_{3}C{H}_{2}CHO}\stackrel{\mathrm{Al}(\mathrm{OC}{}_2\mathrm{H}{}_5){}_3}{\to }\underset{\text{n -propylpropionate}}{C{H}_{3}C{H}_{2}COO{C}_3{H}_7}+H_{2}O$
[d] Reimer-Tiemann reaction: Phenol reacts with $CC{l}_4$ in presence of $NaOH$ at $340K$ to form salicylic acid.