SYNTHESIS OF DIBUTYLAMINE

Dibutyl cyanamide:

• Equip a 2-litre three-necked flask with a reflux condenser and a sealed stirrer unit. 

• Place 220 ml of water and 50g of finely crushed ice in the flask and add slowly, with vigorous stirring, 70g (0.46 mol) of commercial calcium cyanamide (1). 

• As soon as the solid is thoroughly suspended, fit a separatory funnel into the third neck of the flask and introduce through it a cold solution of 34g (0.85 mol) of sodium hydroxide in 70 ml of water; replace the funnel by a thermometer. 

• Continue the vigorous stirring for 1 hour to complete the decomposition of the calcium cyanamide; if the temperature rises above 25 °C, add a little more ice. 

• Add to the resulting solution of sodium cyanamide a solution of 134g (195 ml, 1 mol) of butyl bromide in 220 ml of rectified spirit. 

• Heat the mixture, with stirring, on a water bath until it refluxes gently; continue the refluxing and stirring for 2.5 hours. 

• Replace the reflux condenser by one set for downward distillation and distil the mixture until 165-170 ml of liquid are collected: stir during distillation. 

• Cool the residue in the flask and filter it, with suction, through a Buchner or sintered glass funnel, and wash the residue with rectified spirit. 

• Extract the filtrate, which separates into two layers, first with 90 ml and then with 45 ml of benzenes Dry the combined benzene extracts with anhydrous calcium sulphate, and remove the benzene on a rotary evaporator. 

• Distil under reduced pressure and collect the dibutyl cyanamide at 147-161 °C/35 mm. The yield is 33g(47%).

Dibutylamine:

• Into a 1-litre round-bottomed flask furnished with a reflux condenser place a solution of 34g (18.5 ml) of concentrated sulphuric acid in 100 ml of water: add 33g (0.2 mol) of dibutyl cyanamide and a few fragments of porous porcelain. 

• Reflux gently for 6 hours. 

• Cool the resulting homogeneous solution and pour in a cold solution of 52g of sodium hydroxide in 95 ml of water down the side of the flask so that most of it settles at the bottom without mixing with the solution in the flask. 

• Connect the flask with a condenser for downward distillation and shake it to mix the two layers; the free amine separates. 

• Heat the flask, when the amine with some water distils: continue the distillation until no amine separates from a test portion of the distillate. 

• Estimate the weight of water in the distillate and add about half this amount of potassium hydroxide in the form of pellets so that it dissolves slowly. 

• Cool the solution in ice while the alkali hydroxide is dissolving; some ammonia gas is evolved. 

• When the potassium hydroxide has dissolved, separate the amine, and dry it for 24 hours over sodium hydroxide pellets. 

• Filter and distil from a flask fitted with a Claisen still-head. Collect the dibutylamine at 157-160 °C. The yield is 21g (75%).

Notes to keep in mind:

1. Also known as 'nitrolim'. The fresh product contains approximately 55 per cent of calcium cyanamide, 20 per cent of lime, 12 per cent of graphite and small amounts of other impurities. It should be protected from moisture when stored in order to prevent slow polymerisation to dicyanodiamide.