Q. Phenol can be converted into salicylic acid by:
Delhi UMET/DPMTDelhi UMET/DPMT 2002
Solution:
[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. $\underset{\text { formaldehyde }}{ HCHO }+ NaOH \rightarrow \underset{\text { sodium formate }}{ HCOONa } +\underset{\text { methyl alcohol }}{ CH _{3} OH }$
[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.
$\underset{\text{benzaldehyde}}{C_6H_5CHO} +\underset{\text{acetic anhydride}}{(CH_3CO)_2O} \ce{->[CH_3COONa]}$
$\underset{\text{cinnamic acid}}{C_6H_5CH =CHCOOH} +CH_3COOH$
[c] Tischenko reaction: All the aldehydes on reaction with aluminium ethoxide form esters.
$\underset{\text{propanaldehyde}}{2CH_3CH_2CHO} \ce{->[Al(OC_2H_5)_3]} \underset{\text{n -propylpropionate}}{CH_3CH_2COOC_3H_7} + H_2O$
[d] Reimer-Tiemann reaction: Phenol reacts with $CCl_4$ in presence of $NaOH$ at $340\, K$ to form salicylic acid.
