question_answer 30)

Explain the following with an example. (i) Kolbe's reaction. (ii) Reimer-Tiernann reaction. (iii) Williamson ether synthesis. (iv) Unsymmetrical ether.   (i) (Reaction of phenol with and ), Salicylic acid is formed. (ii) Reaction of phenol with salicylaldehyde. (iii) AlkyI halide + sod. alkoxide Ether + Sod. halide. (iv) Ethers containing two different alkyl/aryl groups.  

Answer:

(i) Kolbe's reactionWhen phenol reacts with sodiumhydroxide, reactive phenoxide ion is formed. So, electrophilicaromatic substitution takes place with  under a pressure of 4-7atm followed by acidification and orthohydroxybenzoic acid(Salicylic acid) is formed. This is called Kolbe's reaction.   (ii) Reimer-Tiemann reaction When phenol is treated withchloroform in the presence of sodium hydroxide, ?CHO group isintroduced at ortho position of benzene ring. This is calledReimer-Tiemann reaction.       (iii) Williamson   ether   synthesis Ethers   (symmertical   andunsymmertrical) are prepared by this method. It involves thereaction of an alkyl halide with sodium alkoxide. e.g., 1. 2. (iv) Unsymmetrical etherAn ether in which alkyl or aryl groupsattached to the oxygen atom are different, is known asunsymmetrical ether. For example, ethyl methyl ether methyl phenyl ether  etc.