Example 7.7

Example . (iii) (i) (iii) (i) . Electrophilic substitution The alkoxy group (-OR) is ortho , para directing and activates the aromatic ring towards electrophilic substitution in the same way as in phenol. (i) Halogenation : Phenylalkyl ethers undergo usual halogenation in the benzene ring, e.g. , anisole undergoes bromination with bromine in ethanoic acid even in the absence of iron (III) bromide catalyst. It is due to the activation of benzene ring by the methoxy group. Para isomer is obtained in % yield. . Write the reactions of Williamson synthesis of -ethoxy- -methylpentane starting from ethanol and -methylpentan- -ol. . Which of the following is an appropriate set of reactants for the preparation of -methoxy- -nitrobenzene and why? (i) (ii) Friedel-Crafts reaction : Anisole undergoes Friedel-Crafts reaction, i.e. , the alkyl and acyl groups are introduced at ortho and para positions by reaction with alkyl halide and acyl halide in the presence of anhydrous aluminium chloride (a Lewis acid) as catalyst. (iii) Nitration : Anisole reacts with a mixture of concentrated sulphuric and nitric acids to yield a mixture of ortho and para nitroanisole. . Predict the products of the following reactions: O – CH HBr − − − + → OC H HI ( ) −  →  (iii) (iv) Alcohols and phenols are classified (i) on the basis of the number of hydroxyl groups and (ii) according to the hybridisation of the carbon atom, sp or sp to which the –OH group is attached. Ethers are classified on the basis of groups attached to the oxygen atom. Alcohols may be prepared ( ) by hydration of alkenes (i) in presence of an acid and (ii) by hydroboration-oxidation reaction ( ) from carbonyl compounds by (i) catalytic reduction and (ii) the action of Grignard reagents. Phenols may be prepared by ( ) substitution of (i) halogen atom in haloarenes and (ii) sulphonic acid group in aryl sulphonic acids, by –OH group ( ) by hydrolysis of diazonium salts and ( ) industrially from cumene. Alcohols are higher boiling than other classes of compounds, namely hydrocarbons, ethers and haloalkanes of comparable