Q.With a suitable example, write equations for the following:

Four classic named reactions of alcohols/phenols and carbonyl/carboxylic-acid chemistry: Kolbe's (phenol to salicylic acid), Williamson's (ether synthesis), Cannizaro's (self redox of an aldehyde without alpha-H), and decarboxylation (loss of CO2 from a carboxylate).

1. Kolbe's reaction (Kolbe-Schmitt reaction): Sodium phenoxide (formed from phenol + NaOH) is treated with carbon dioxide at high temperature (~400 K) and pressure (4-7 atm); the CO2 attacks the highly electron-rich ortho position of the phenoxide ring. The resulting product is acidified with dilute acid to give ortho-hydroxybenzoic acid (salicylic acid). C6H5OH + NaOH -> C6H5ONa + H2O (sodium phenoxide) C6H5ONa + CO2 --(heat, pressure)--> sodium salicylate (ortho-C6H4(OH)COONa) sodium salicylate + H+ (dil. HCl) -> salicylic acid, ortho-C6H4(OH)COOH + NaCl
2. Williamson ether synthesis: An alkyl halide is treated with sodium alkoxide (prepared by reacting an alcohol with sodium metal). This proceeds by an SN2 mechanism - the alkoxide ion (a good nucleophile) attacks the electrophilic carbon of the alkyl halide, displacing the halide ion, forming an ether. R-X + R'-O-Na+ -> R-O-R' + NaX (For best results, the alkyl halide should be primary; a bulky/secondary or tertiary halide favours elimination instead of substitution.) Example: CH3Br + C2H5ONa -> CH3-O-C2H5 (ethyl methyl ether) + NaBr
3. Cannizaro reaction: Aldehydes that do not have an alpha-hydrogen atom (i.e., cannot undergo aldol condensation) undergo self oxidation-reduction (disproportionation) when treated with concentrated alkali (NaOH). In this reaction, one molecule of the aldehyde is reduced to the corresponding alcohol while another molecule of the same aldehyde is oxidised to the corresponding carboxylic acid salt. …