SYNTHESIS OF BUTYLBENZENE (2-Phenylbutane)

• Equip a 500-ml three-necked flask as detailed for p-toluic acid and pass a slow stream of nitrogen through the apparatus. 

• Charge the flask with 150 ml of sodium dried, sulphur-free toluene and 13.8g (0.6mol) of sodium wire. 

• Place 34g (31ml, 0.3 mol) of chlorobenzene in the dropping funnel and add it dropwise through the condenser during 1 hour, with vigorous stirring, while maintaining the temperature inside the flask at 30-35 °C. 

• The start of the reaction is indicated by the appearance of black specks on the sodium surface. (If the reaction is slow to start, it may be instantly initiated by a few drops of butanol.) Complete the formation of phenylsodium by stirring for 2-3 hours at 30 °C.

• Attach a calcium chloride tube to the top of the reflux condenser and reflux the mixture for 40 minutes. 

• The reflux temperature, initially 107 °C, gradually falls to 103 °C as benzene is formed by the exchange reaction. 

• Remove the heating bath and add 27.6 g (20.5 ml, 0.224 mol) of redistilled propyl bromide during 20-25 minutes at 103-105 °C; the reaction is strongly exothermic. 

• Allow the reaction mixture to cool to room temperature: maintain the stirring and the slow stream of nitrogen. 

• Add water slowly to destroy the excess of sodium. 

• Separate the toluene layer, dry it (magnesium sulphate) and distil it through a short, jacketed column filled with glass helices (19 cm packed length, 14 mm diameter;). 

• After removal of the toluene (up to 111 °C) and a small intermediate fraction (11 1-179 °C), pure butylbenzene passes over at 179.5-181 °C/752 mmHg (23g, 77%). 

• A brown residue (4g) remains in the flask. 

• The i.r. spectrum shows absorptions at c. 3050 and 2950 cm⁻¹ for the aromatic and alkyl carbon-hydrogen stretching vibrations respectively, at 1600, 1590 and 1500 cm⁻¹ for the ring breathing vibrations (the 1450 cm¹ absorption is obscured by the alkyl carbon-hydrogen deformation vibrations), at c. 700 and 750 cm⁻¹ characteristic of monosubstitution, and well-defined summation bands at 1600-2000 cm⁻¹. 

• The p.m.r. spectrum (CCl₄, TMS), shows signals at 𝛿 0.92 (t, 3H, Me), 1.10-1.80 (m, 4H, — CH₂CH₂—), 2.58 (t, 2H, ArCH₂) and 7.09 (s, 5H, C— H). The m.s. shows significant fragment ions at m/z 134 (M), 105 (M - C₂H₅), 91 (M - C₃H₇, base peak), and 65 (91 - C₂H₂).