SYNTHESIS OF HEXANE-1-THIOL

CAUTION: This preparation must be carried out in an efficient fume cupboard; disposable plastic gloves should be worn when handling thiourea.

• Into a 500-ml two-necked flask, equipped with a sealed stirrer unit and a reflux condenser, place 62.5g (53.5 ml, 0.38 mol) of 1-bromohexane and a solution of 35g (0.5 mol) of thiourea in 25 ml of water. 

• Connect a tube from the top of the condenser leading to an inverted funnel just immersed in potassium permanganate solution in order to prevent the escape of unpleasant odours. 

• Stir the mixture vigorously and heat under reflux for 2 hours; the mixture becomes homogeneous after about 30 minutes and the additional heating ensures the completeness of the reaction. 

• Add a solution of 30g of sodium hydroxide in 300 ml of water and reflux, with stirring, for a further 2 hours; during this period the thiol separates since it is largely insoluble in the alkaline medium. 

• Allow to cool and separate the upper layer of almost pure hexane-1-thiol (35g). 

• Acidify the aqueous layer with a cold solution of 75 ml of concentrated sulphuric acid in 50 ml of water, and extract it with 75 ml of ether. 

• Combine the ethereal extract with the crude thiol, dry with anhydrous sodium sulphate and remove the ether on a water bath. 

• Distil the residue using an air bath and collect the hexane-1-thiol at 150-152 °C. The yield is 37.5g (84%).

Cognate preparation: Butane-1-thiol

• Use 51g (40 ml, 0.372 mol) of butyl bromide, 38g (0.5 mol) of thiourea and 25 ml of water. 

• Reflux, with stirring, for 3 hours; the mixture becomes homogeneous after 1 hour. 

• Allow to cool and separate the upper layer of the thiol (A). 

• Acidify the aqueous layer with a cold solution of 7 ml of concentrated sulphuric acid in 50 ml of water, cool and saturate with salt; remove the upper layer of butane-1-thiol (B) and combine it with (A). 

• Extract the aqueous liquid with 75 ml of ether, dry the ethereal extract with sodium sulphate or calcium sulphate and distil off the ether from a water bath through a fractionating column. 

• Combine the residue with (A) and (£), and distil. 

• Collect the butane-1-thiol at 97-99 °C. The yield is 24g (72%).

General remarks on the preparation of thiols:

• The above method is of quite general application. 

• If the bromoalkane is inexpensive, the extraction with ether may be omitted, thus rendering the preparation of thiols a comparatively easy and not unduly unpleasant operation. 

• The following thiols may be prepared in yields of the same order as hexane-1-thiol and butane-1-thiol; ethanethiol, b.p. 35-36 °C; propane-1-thiol, b.p. 66-67 °C; propane-2-thiol, b.p. 51-52°C; 2-methylpropane-1-thiol, b.p. 87-88 °C; pentane-1 -thiol, b.p. 124-125 °C; heptane-1-thiol, b.p. 175-176 °C; octane-1-thiol, b.p. 198-200 °C or 98-100 °C/22mmHg; nonane-1-thiol, b.p. 220-222 °C or 98-100 °C/15mmHg; decane-1 -thiol, b.p. 96-97 °C/5 mmHg or 114°C/13mmHg; undecane-1-thiol, b.p. 103-104 °C/3 mmHg; dodecane-1-thiol, b.p. 111- 112°C/3mmHg or 153-155 °C/24 mmHg; tetradecane-1-thiol, b.p. 176-180°C/22mmHg; phenylmethanethiol, b.p. 195 °C.