SYNTHESIS OF t-BUTYLBENZENE (2-Methyl-2-pheny\propane)

CAUTION: This preparation should be conducted in an efficient fume cupboard.

• Place 50g (0.33 mol) of anhydrous aluminium chloride (1) Into a 1-litre three-necked flask and 200 ml (2.25 mol) of dry benzene (CAUTION); cool in a bath of crushed ice. 

• Stir the mixture and add 50g (59 ml, 0.54 mol) of t-butyl chloride from the dropping funnel during 4-5 hours; the first addition should be 3-4 ml in order to prevent the benzene from freezing. 

• Maintain the mixture at a temperature of 0-5 °C by the addition of salt to the ice, if necessary. 

• When all the t-butyl chloride has been run in, continue the stirring for 1 hour longer. 

• Remove the separatory funnel and add 200g of finely crushed ice in small portions with stirring; finally add 100 ml of cold water to complete the decomposition of the intermediate addition compound. 

• Arrange the flask for steam distillation and steam distil the resulting reaction mixture. 

• Transfer the steam distillate to a separatory funnel, remove the upper hydrocarbon layer, extract the water layer with two 50 ml portions of ether and combine the extracts with the upper layer. 

• Dry with magnesium sulphate, distil off the ether on a water bath and fractionally distil the residue twice, using a well-lagged column. 

• Collect the t-butylbenzene at 165-170 °C. The yield is 45g (62%). Pure t-butylbenzene boils at 168.5 °C. 

• Note the characteristic absorptions for the aromatic system at c. 3050 cm⁻¹ , at 1600, 1590 and 1500 cm⁻¹ and at c. 700 and 765 cm⁻¹ for a monosubstituted nucleus. The t-butyl group shows characteristic carbon-hydrogen stretching absorptions at c. 2950 cm⁻¹.

Notes to Keep in Mind:

1. In an alternative procedure 25g of anhydrous iron(m) chloride replace the aluminium chloride, the mixture is cooled to 10 °C and the 50g of t-butyl chloride are added. The mixture is slowly warmed to 25 °C and maintained at this temperature until no more hydrogen chloride is evolved. The reaction mixture is then washed with dilute hydrochloric acid and with water, dried and fractionally distilled. The yield of t-butyl benzene, b.p. 167-170 °C, is 60g.