SYNTHESIS OF VALERONITRILE (Butyl cyanide)

CAUTION: Sodium and potassium cyanide are very poisonous and should be handled with great care; disposable plastic gloves should be worn. Alkyl cyanides are likewise very poisonous and all operations should be conducted in an efficient fume cupboard.

• Set up on a water bath a 500-ml three-necked flask fitted with a mechanical stirrer, a thermometer and a two-way adapter fitted with a dropping funnel and a reflux condenser protected by a calcium chloride guard-tube. 

• Place 150 ml of dry dimethyl sulphoxide in the flask and add 30g (0.61 mol) of dry powdered sodium cyanide. 

• Heat the mixture with stirring to 90 °C and then remove the water bath. 

• Add 46.3g (0.5 mol) of butyl chloride slowly from the dropping funnel so that the temperature of the exothermic reaction does not rise above 150 °C (about 10 minutes); continue to stir until the temperature falls to 50 °C (about 30 minutes). 

• Pour the mixture into water and extract with three 300 ml portions of ether. 

• Wash the combined extracts with two 100 ml portions of saturated sodium chloride solution, dry over magnesium sulphate and distil off the ether on a water bath. 

• Distil the residue at atmospheric pressure and collect the butyl cyanide at 138-140 °C; the yield is 35.2 g (85%). The product has a nauseating odour, and should be handled in an efficient fume cupboard.

Cognate preparations: Octanenitrile

• Use 250 ml of dry dimethyl sulphoxide, 89.6g (0.5 mol) of 1-bromoheptane and 30g (0.61 mol) of dried sodium cyanide. The yield of octanenitrile is 50.8 g (81%), b.p. 199-203 °C.

Hexanedinitrile (adiponitrile):

• Use 150 ml of dry dimethyl sulphoxide, 21.2g (0.17 mol) of 1,4-dichlorobutane and 20g (0.41 mol) of dried sodium cyanide. 

• Maintain the reaction temperature at 90 °C for a further 15 minutes after the initial exothermic reaction has subsided. 

• Add 150 ml of dichloromethane to the cooled reaction mixture and pour into an excess of saturated sodium chloride solution in a separatory funnel. 

• Add just sufficient water to dissolve precipitated salts and separate the dichloromethane layer. 

• Extract the acqueous layer once with dichloromethane, wash the combined extracts twice with salt solution, dry over magnesium sulphate and remove the solvent using a rotary evaporator. 

• Fractionally distil the residue under reduced pressure and collect the adiponitrile as a fraction of b.p. 140-141 °C/ 1.5mmHg. The yield is 14.6g (81%). Some dimethyl sulphoxide (b.p. 40-42°C/1.5mmHg) may be obtained as a forerun.