SYNTHESIS OF 1-CHLOROHEXANE

• Reaction in the absence of catalyst. 

• Assemble in a fume cupboard a 500-ml three-necked flask equipped with a sealed stirrer unit, a double surface reflux condenser and a separatory funnel; fit the condenser and the funnel with calcium chloride guard-tubes. 

• Place 179 g (109.5 ml, 1.5 mol) of redistilled thionyl chloride in the flask and 51 g (62.5 ml, 0.5 mol) of hexan-1-ol, b.p. 156-158 °C, in the separatory funnel. 

• Add the alcohol with stirring during 2 hours; there is a slight evolution of heat, sulphur dioxide is evolved and the liquid darkens considerably. 

• When all the alcohol has been added, reflux the mixture for 2 hours. 

• Rearrange the apparatus for distillation, and distil slowly; the excess of thionyl chloride passes over below 80 °C, followed by a small fraction up to 120 °C; and finally the crude 1-chlorohexane at 132— 134 °C. Wash the last-named successively with water, 10 per cent sodium carbonate solution, and twice with water. 

• Dry with anhydrous calcium chloride and distil through a short fractionating column. Pure 1-chlorohexane passes over at 133-1 34 °C. The yield is 36 g (60%).

Cognate preparations: 1-Chloroheptane

• From 58 g (70.5 ml, 0.5 mol) of heptan-1-ol (b.p. 175-177°C) and 179g (109.5ml, 1.5 mol) of redistilled thionyl chloride; refluxing period, 4 hours. The yield of 1-chloroheptane, b.p. 159-1 60 °C, is 52g(77%).

1-Chlorododecane:

• From 46.5 g (0.25 mol) of dodecan-1-ol (lauryl alcohol), m.p. 24 °C, and 1 19 g (73 ml, 1 mol) of redistilled thionyl chloride; refluxing period, 6 hours. 

• The crude chloride passes over at 252-257 °C, mainly at 255- 257 °C. 

• Upon redistillation under reduced pressure 35 g (68%) of 1-chlorododecane, b.p. 116.5°C/5mmHg, are obtained.

1,4-Dichlorobutane:

• Place 22.5 g (0.25 mol) of redistilled butane- 1,4-diol and 3 ml of dry pyridine in the flask in an ice bath. 

• Add 119 g (73 ml, 1 mol) of redistilled thionyl chloride dropwise to the vigorously stirred mixture at such a rate that the temperature remains at 5-10 °C. 

• When the addition is complete, remove the ice bath, keep the mixture overnight and then reflux for 3 hours. 

• Cool, add ice-water cautiously and extract with ether. 

• Wash the ethereal extract successively with 10 per cent sodium hydrogen carbonate solution and water, and dry with magnesium sulphate. 

• Remove the ether by flash distillation and distil the residue under reduced pressure. 

• Collect the 1,4- dichlorobutane at 55.5-56.5 °C/14mmHg; the yield is 18 g (58%). The b.p. under atmospheric pressure is 154-155 °C.

Isobutyl chloride (l-chloro-2-methylpropane): 

• Reaction in the presence of pyridine. 

• Place 37 g (46ml, 0.5 mol) of 2-methylpropan-l-ol (b.p. 106-108 °C) and 40 g (41 ml, 0.5 mol) of pure pyridine (CAUTION) in the flask, and 1 1 9 g (73 ml, 1.0 mol) of redistilled thionyl chloride in the funnel. 

• Introduce the thionyl chloride with stirring during 3-4 hours; a white solid separates, which partially dissolves as the reaction proceeds. 

• Reflux for 45 minutes: the solid will dissolve completely. 

• Allow to cool and remove the upper layer. 

• Wash the latter cautiously with water, 5 per cent sodium hydroxide solution, and twice with water; dry with anhydrous calcium chloride. 

• Distil the product through a short fractionating column and collect the isobutyl chloride at 68-69 °C.

• The yield is 26 g (56%). 

• Record the p.m.r. spectrum (CC1 4 , TMS) and assign the signals which appear at 8 1.03 (d, 6H), 1.91 (m, 1H) and 3.32 (d, 2H). 

• The base peak in the m.s. appears at m/z 43 [M — ( — CH 2 35,37 C1) and corresponds to the isopropyl carbocation.

General procedure for reactions in the presence of dimethylformamide: 

• 85 Thio- nyl chloride (1.1 mol) followed by the alcohol (1 mol) is added dropwise to dimethylformamide (40 ml) at 0-10 °C (1). 

• The reaction is heated as specified below, cooled and excess water added. 

• The upper layer is then washed, dried (K 2 C0 3 ) and distilled. 

• The following conditions are specified: neopentyl alcohol (150 °C, 2 hours), pentan-3-ol (100 °C, 0.5 hours), 3-methylbutan-2-ol (100 °C, 0.5 hours).

Notes to keep in mind:

1. The dimethylformamide is dried over molecular sieves.