SYNTHESIS OF OCTANE

STEP 1: Weigh out 23 g (1 mol) of clean sodium under sodium-dried ether, cut it up rapidly into small pieces and introduce the sodium quickly into a dry 750- or 1000-m1 round-bottomed flask. 

STEP 2: Fit a dry 30-cm double surface condenser (e.g. of the Davies type) into the flask and clamp the apparatus so that the flask can be heated on a wire gauze. 

STEP 3: Weigh out 68.5 g (53 ml, 0.5 mol) of butyl bromide previously dried over anhydrous sodium sulphate. 

STEP 4: Introduce about 5 ml of the bromide through the condenser into the flask. 

STEP 5: If no reaction sets in, warm the flask gently with a small lumin­ous flame; remove the flame immediately reaction commences (the sodium will acquire a blue colour). 

STEP 6: When the reaction subsides, shake the contents of the flask well; this will generally produce further reaction and some of the sodium may melt. 

STEP 7: Add a further 5 ml of butyl bromide, and shake the flask. 

STEP 8: When the reaction has slowed down, repeat the above process until all the alkyl bromide has been transferred to the flask (about 1.5 hours). 

STEP 9: Allow the mixture to stand for 1-2 hours. 

STEP 10: Then add down the condenser by means of a dropping funnel 50 ml of rectified spirit dropwise over 1.5 hours, followed by 50 ml of 50 per cent aqueous ethanol during 30 minutes, and 50 ml of distilled water over 15 minutes; shake the flask from time to time. 

STEP 11: Add 2-3 small pieces of porous porcelain and reflux the mixture for 3 hours; any unchanged butyl bromide will be hydrolysed. 

STEP 12: Add a large excess (500-750 ml) of water, and separate the upper layer of crude octane (17-18 g). 

STEP 13: Wash it once with an equal volume of water, and dry it with magnesium sulphate. Distil through a short fractioning side-arm and collect the fraction, b.p. 123­126 °C (15 g, 52%) (1).

Notes to keep in mind:

1. All hydrocarbons prepared by the Wurtz reaction contain small quantities of unsaturated hydrocarbons. These may be removed by shaking repeatedly with 10 per cent of the volume of concentrated sulphuric acid until the acid is no longer coloured (or is at most extremely pale yellow); each shaking should be of about 5 minutes' duration. The hydrocarbon is washed with water, 10 per cent sodium car­bonate solution, water (twice), and dried with magnesium sulphate or anhydrous cal­cium sulphate. It is then distilled from sodium; two distillations are usually necessary.