(a) Illustrate the following name reactions giving a chemical equations in each case :
(i) Clemmensen reaction
(ii) Cannizzaro's reaction
(b) Describe how the following conversions can be brought about :
(i) Cyclohexanol to cyclohexan 1 - one
(ii) Ethylbenzene to benzoic acid
(iii) Bromobenzene to benzoic acid

Explanation

(a) (i) Clemmensen reaction : See Q 33 (a) (ii), Set - I, Delhi Board, 2009.
(ii) Cannizaro's reaction : Aldehydes which do not contain any ` alpha`- hydrogen atom such as formaldehyde HCHO and benzaldehyde ` C_(6) H_(5) CHO` undergo self oxidation and reduction reaction on treatment with concentrated alkali. A mixture of an alcohol and a salt of a carboxlic acid is formed.
`underset("Methanol")(HCHO +HCHO)overset("NaOH")to underset("Mathanol")(CH_(3)OH)+underset("Sod. formate")(HCOONa)`
`underset("Benzaldehyde")(C_(6)H_(5)CHO+C_(6)H_(5)CHO)overset(NaOH)to underset("Benzyl")(C_(6)H_(5)CH_(2))underset("alcohol")(OH)+underset("Sod. benzoate")(C_(6)H_(5)COO Na)`
(b)