SYNTHESIS OF CHLOROCYCLOHEXANE (Cyclohexyl chloride)

• In a 1 -litre, round-bottomed two-necked flask, carrying a reflux condenser  and mechanical stirrer, place lOOg (1 mol) of pure cyclohexanol, 250ml of concentrated hydrochloric acid and 80 g of anhydrous calcium chloride: heat the mixture on a boiling water bath for 10 hours with stirring (1).

• Some hydrogen chloride is evolved, consequently the preparation should be conducted in the fume cupboard. 

• Separate the upper layer from the cold reaction product, wash it successively with saturated salt solution, saturated sodium hydrogen carbonate solution, saturated salt solution, and leave the crude chlorocyclohexane over an excess of anhydrous calcium chloride for at least 24 hours. 

• Distil from a 150-ml flask through a fractionating side-arm, and collect the pure product at 141.5-142.5 °C. The yield is 90 g (76%).

Notes to keep in mind:

1. The refluxing period may be reduced to 6 hours and the yield improved  slightly by echanical stirring; a three-necked flask should be used.

• An alternative method of conducting the preparation consists in treating 100 g of cyclohexanol with 250 ml of concentrated hydrochloric acid, refluxing slowly while a stream of hydrogen chloride gas is passed into the mechanically stirred mixture for 3 hours. (The apparatus required is similar to that described for a Clemmensen reduction) Chlorocyclohexane, b.p. 141-143 °C, is isolated as above; the yield is 80 g.

Cognate preparations: Chlorocyclopentane (cyclopentyl chloride)

• Use 43 g (0.5 mol) of cyclopentanol (Expt 5.29), 125 ml of concentrated hydrochloric acid and 50 g of anhydrous calcium chloride. The yield of chlorocyclopentane, b.p. 113-1 15 °C, is 30 g (57%). 

AllyI chloride:

• Place 87g (100ml, 1.5 mol) of allyl alcohol, 150 ml of concentrated hydrochloric acid and 2g of freshly prepared copper(i) chloride in a 750-ml round-bottomed flask equipped with a reflux condenser. 

• Cool the flask in ice and add 50 ml of concentrated sulphuric acid dropwise through the condenser with frequent shaking of the flask. 

• A little hydrogen chloride may be evolved towards the end of the reaction. 

• Allow the turbid liquid to stand for 30 minutes in order to complete the separation of the allyl chloride. 

• Remove the upper layer, wash it with twice its volume of water, and dry over anhydrous calcium chloride. 

• Distil and collect the allyl chloride which passes over at 46-47 °C; the yield is about lOOg (87%). 

• Interpret the following data from the m.s.; m/z 78 (RA 9.3%), 76 (RA 27.8%), 41 (RA 100%), 40 (RA 11.7%) and 39 (RA 72.5%).