SYNTHESIS OF DIPROPYL SULPHIDE

CAUTION: This preparation must be carried out in an efficient fume cupboard. 

• Place 56g (0.5 mol) of finely powdered, fused sodium sulphide and 100 ml of rectified spirit in a 500-ml round-bottomed flask equipped with a reflux condenser. 

• To the boiling mixture add 46g (34 ml, 0.374 mol) of propyl bromide slowly and reflux for 6 hours. 

• Distil off the ethanol on a water bath, and add a large excess of water to the distillate. 

• Separate the upper layer of crude sulphide, wash it with three 40-ml portions of 5 per cent sodium hydroxide solution, then with water until the washings are neutral, and dry over anhydrous calcium chloride or anhydrous calcium sulphate. 

• Distil, and collect the dipropyl sulphide at 141-143 °C. The yield is 20g (91%). If the sulphide is required perfectly pure, it should be redistilled from a little sodium.

Cognate preparation: Dibenzyl sulphide

• Heat a solution of 63g (0.5 mol) of benzyl chloride in 160 ml of rectified spirit on a steam bath and stir while adding a solution of 29g (0.25 mol) of fused sodium sulphide in about 50-60 ml of water. 

• Continue stirring and heating for 3 days, remove the ethanol on a rotary evaporator and pour the residue on to 350g of crushed ice. 

• Separate the oil and triturate with a little 70 per cent ethanol to crystallise the product. Recrystallise from the same solvent; the yield of dibenzyl sulphide is 26g (83%), m.p. 49 °C.