SYNTHESIS OF PENTANEDINITRILE (Glutaronitrile)

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.

• Fit a 2-litre two-necked flask with a separatory funnel and a reflux condenser. 

• Place 147g (3 mol) of finely powdered sodium cyanide (1) and 150 ml of water in the flask and heat on a water bath until most of the solid passes into solution. 

• Add a solution of 250g (126 ml, 1.25 mol) 1,3-ibromopropane in 500 ml of rectified spirit through the separatory funnel over a period of 30 minutes. 

• Reflux the mixture on a water bath for 35 hours; then remove the solvent (rotary evaporator) using a boiling-water bath. 

• The residue in the flask consists of sodium bromide, unreacted sodium cyanide and the dinitrile: the last-named alone is soluble in ethyl acetate. 

• Extract the residue with 200 ml of ethyl acetate. Filter the solution through a sintered glass funnel and wash the solid with about 50 ml of ethyl acetate. 

• Dry the filtrate, after removing the aqueous layer, with anhydrous calcium sulphate, distil off the ethyl acetate at atmospheric pressure (about 245 ml are recovered), allow to cool somewhat and distil the liquid under reduced pressure. 

• Collect the pentanedinitrile at 139-140 °C/8mmHg. The yield is 95g (82%); ¹³C-n.m.r. spectrum (CDCl₃ , TMS) 𝛅 16.3, 21.6 and 118.8; i.r. spectrum (thin film) 2200 cm⁻¹ (CN).

Notes to keep in mind: 

1.  Dry the powdered commercial material (c. 98% pure) in a vacuum desiccator over potassium hydroxide pellets. Sodium cyanide is very poisonous and must be handled with great care. Residual solutions containing alkali cyanides should be rendered innocuous by the addition of an excess of sodium hypochlorite before being washed down the main drain of the laboratory with a liberal supply of water; they should never be treated with acid.

Cognate preparations: Heptanenitrile

• Use 30g (0.61 mol) of sodium cyanide dissolved in 40 ml of water; 82g (70 ml, 0.5 mol) of 1-bromohexane in 150 ml of methanol. 

• Remove the methanol through an efficient fractionating column, add 500 ml of water and separate the upper layer of crude nitrile. 

• Purify the crude nitrile by shaking it twice with about half its volume of concentrated hydrochloric acid, and then successively with water, saturated sodium hydrogen carbonate solution and water. 

• Dry with anhydrous calcium chloride and distil. 

• Collect the heptanenitrile at b.p. 182-184 °C. The yield is 40g (73%).

Heptanedinitrile:

• Use 29g (0.446 mol) of potassium cyanide, 30 ml of water and 45g (0.195 mol) of 1,5-dibromopentane in 75ml of rectified spirit. 

• Reflux for 8 hours and work-up as for pentanedinitrile but using ether as the extracting solvent. 

• Distil the crude heptanedinitrile under diminished pressure and collect the main fraction at b.p. 168-170 °C/15 mmHg. The yield is 18g (75%).

Octanedinitrile:

• 1,6-Dibromohexane may be converted into octanedinitrile, b.p. 178-180°C/15mmHg, as in the foregoing experiment.

Benzyl cyanide:

• Place 100 g (2 mol) of powdered sodium cyanide and 90 ml of water in a 1 -litre round-bottomed flask provided with a reflux condenser. 

• Warm on a water bath until the sodium cyanide dissolves. 

• Add down the condenser a solution of 200g (181.5 ml, 1.58 mol) of benzyl chloride in 200 g of rectified spirit during 30-45 minutes. 

• Heat the mixture in a water bath for 4 hours, cool and filter off the precipitated sodium chloride with suction; wash with a little alcohol. 

• Distil off as much as possible of the alcohol using a rotary evaporator. 

• Cool the residual liquid, filter if necessary and separate the layer of crude benzyl cyanide. (Sometimes it is advantageous to extract the nitrile with ether.) 

• Dry over a little magnesium sulphate, and distil under diminished pressure. 

• Collect the benzyl cyanide at 102-103 °C/10mmHg. The yield is 160g (86%). 

• This product is sufficiently pure for most purposes but it contains some benzyl isocyanide and usually develops an appreciable colour on standing. 

• The following procedure removes the isocyanide and gives a stable water-white compound. 

• the once-distilled benzyl cyanide vigorously for 5 minutes with an equal volume of warm (60 °C) 50 per cent sulphuric acid (prepared by adding 55 ml of concentrated sulphuric acid to 100 ml of water). 

• Separate the benzyl cyanide, wash it with an equal volume of saturated sodium hydrogen carbonate solution and then with an equal volume of half-saturated sodium chloride solution. 

• Dry with magnesium sulphate and distil under reduced pressure.

1-Naphthylacetonhrile:

• Place a mixture of 56g (0.32 mol) of l-(chloro-methyl)naphthalene, 29g (0.45 mol) of potassium cyanide, 125 ml of ethanol and 50 ml of water in a 500-ml round-bottomed flask fitted with a double surface reflux condenser, and reflux for 1 hour. 

• Distil off the alcohol, transfer the residue to a separatory funnel, wash it with water, filter from a small amount of solid, transfer to a dish and dry under reduced pressure (vacuum desiccator charged with anhydrous calcium chloride). 

• Distil under diminished pressure and collect the 1-naphthylacetonitrile at 155-160 °C/9mmHg (1); the yield is 38g(72%).

Notes to keep in mind:

1.  A little naphthalene may pass over first owing to impurities in the original

chloromethylnaphthalene.

 

Allyl cyanide:

• Into a 2-litre three-necked flask, provided with a sealed stirrer and two long double surface condensers, place 293g (210 ml, 2.42 mol) of freshly distilled allyl bromide, b.p. 70-71 °C and 226g (2.52 mol) of dry copper(i) cyanide. 

• Warm the flask on a water bath so that the allyl bromide refluxes but do not stir at this stage. 

• Immediately the vigorous reaction commences (after 15-30 minutes), remove the water bath and cool the flask in a bath of ice and water; the two double surface condensers will prevent any loss of product. 

• When the reaction subsides, start the stirrer and heat the mixture on the water bath for 1 hour. 

• Remove the condensers and arrange the apparatus for distillation: close one neck with a stopper. 

• Heat the flask in an oil bath, and distil the allyl cyanide with stirring; it is advisable to reduce the pressure (water pump) towards the end of the distillation to assist the removal of the final portion of the allyl cyanide from the solid residue. 

• Redistil and collect the pure allyl cyanide at 116-121 °C. The yield is 140g (86%).