SYNTHESIS OF HEXYLBENZENE (1-Phenylhexane)

• Clemmensen reduction. Prepare 200 g of amalgamated zinc in a 2-litre three-necked flask. 

• Fit the flask with a reflux condenser, a sealed stirrer and a gas entry tube reaching to within 1 cm of the bottom; connect the last-named through an intermediate empty wash bottle to a Kipp's apparatus supplying hydrogen chloride gas. 

• Place a mixture of 500 ml of concentrated hydrochloric acid and 100ml of water in the flask and introduce 100g (0.57 mol) of l-phenylhexan-3-one. 

• Stir the mixture and pass a slow stream of hydrogen chloride gas while warming the flask on a suitable wire gauze by means of a small flame. 

• If the reaction becomes unduly vigorous, stop the supply of hydrogen chloride until it subsides somewhat. 

• Most of the zinc dissolves after 6 hours, by which time the reaction is almost complete; allow to stand overnight. 

• Arrange the apparatus for steam distillation and pass steam into the flask, heated by means of a small flame, until the distillate is clear. 

• Separate the upper hydrocarbon layer, wash it with 5 per cent sodium hydroxide solution, then with water and dry over magnesium sulphate. 

• Distil from a 100 ml flask and at 218-230 °C collect the crude hexyl benzene, which contains some unsaturated compounds. 

• These can be removed by repeated shaking with 5 per cent of the volume of concentrated sulphuric acid until the latter is colourless or, at most, very pale yellow. 

• The hydrocarbon is then washed with 5 per cent sodium carbonate solution, then with water and dried over magnesium sulphate. 

• It is then distilled twice from sodium when pure hexylbenzene, b.p. 220-225 °C is obtained. The yield is 40g (43%).