SYNTHESIS OF PENTYLAMINE

• Equip a three- necked 1-litre flask with a dropping funnel, an efficient mechanical stirrer and a reflux condenser. 

• Place 55g (2.4 mol) of clean sodium and 200 ml of sodium-dried toluene in the flask, heat the mixture until the toluene commences to boil and then stir the molten sodium vigorously thus producing an emulsion. 

• Run in through the dropping funnel a mixture of 33g (41.5ml) of butyl cyanide and 60g (76ml) of absolute ethanol during 1 hour. 

• During the addition and the subsequent introduction of ethanol and of water, the stirring should be vigorous and the temperature adjusted so that the refluxing is continuous; the heat of reaction will, in general, be sufficient to maintain the refluxing. 

• After the butyl cyanide solution has been added, introduce gradually a further 60g (76 ml) of absolute ethanol. 

• In order to destroy any residual sodium, treat the reaction mixture slowly with 40g (50 ml) of rectified spirit and then with 20g of water. 

• Steam distil the contents of the flask (about 2 hours) and add 40 ml of concentrated hydrochloric acid to the distillate. 

• Separate the toluene layer; evaporate the aqueous layer, which contains alcohol and amine hydrochloride, to dryness under reduced pressure (rotary evaporator). 

• Treat the resulting amine hydrochloride with a solution of 40g of sodium hydroxide in 200 ml of water. 

• Separate the amine layer, dry it by shaking with sodium hydroxide pellets (prolonged contact is required for complete drying) and distil. 

• Collect the fraction boiling at 102-105 °C as pure pentylamine. 

• Dry the fraction of low boiling point again over sodium hydroxide and redistil; this gives an additional quantity of amine. The total yield is 30g (86%).

Cognate preparation: 2-Phenylethylamine

• Saturate commercial absolute methanol with ammonia (derived from a cylinder) at °C; the resulting solution is c. 10 𝗠. 

• Dissolve 58g (0.5 mol) of benzyl cyanide (1) in 300 ml of the cold methanolic ammonia, and place the solution in a high-pressure hydrogenation bomb, add 10 ml of settled Raney nickel catalyst, securely fasten the cap and introduce hydrogen until the pressure is 500-1000 lb. 

• Set the mechanical stirring device in motion, and heat at 100-125 °C until absorption of hydrogen ceases (about 2 hours). 

• Allow the bomb to cool, open it and remove the contents. 

• Rinse the bomb with two 100 ml portions of anhydrous methanol and pour the combined liquids through a fluted filter paper to remove the catalyst; do not permit the catalyst to become dry since it is likely to ignite. 

• Remove the solvent and ammonia by distillation (fume cupboard), and fractionate the residue through a short column. 

• Collect the 2-phenylethylamine at 92-93°C/18mmHg. The yield is 54g (90%).

Notes to keep in mind:

1. Minute amounts of halide have a powerful poisoning effect upon the catalyst; it is advisable to distil the benzyl cyanide from Raney nickel.