SYNTHESIS OF 1-PHENYLETHYLAMINE (a-Methylbenzylamine)

• Place 126g (2.0 mol) of ammonium formate, 72g (0.6 mol) of acetophenone and a few chips of porous porcelain in a 250-ml flask fitted with a Claisen still-head carrying a short fractionating column; insert a thermometer extending nearly to the bottom of the flask, and attach a short condenser set for downward distillation to the side-arm. 

• Heat the flask with a heating mantle or in an air bath; the mixture first melts to two layers and distillation occurs. 

• The mixture becomes homogeneous at 150-1 55 °C and reaction takes place with slight frothing. 

• Continue the heating, more slowly if necessary, until the temperature rises to 185 °C (about 2 hours); acetophenone, water and ammonium carbonate distil. 

• Stop the heating at 185 °C, separate the upper layer of acetophenone from the distillate and return it without drying to the flask. 

• Heat the mixture for 3 hours at 180-185 °C and then allow to cool; the acetophenone may be recovered from the distillate by extraction with 20 ml portions of toluene(1). 

• Transfer the reaction mixture to a 250-ml separatory funnel and shake it with two 75 ml portions of water to remove formamide and ammonium formate. 

• Transfer the crude (1-phenylethyl)formamide into the original reaction flask; extract the aqueous layer with two 20 ml portions of toluene, transfer the toluene extracts to the flask, add 75 ml of concentrated hydrochloric acid and a few chips of porous porcelain. 

• Heat the mixture cautiously until about 40 ml of toluene are collected, and boil gently under reflux for a further 40 minutes; hydrolysis proceeds rapidly to 1-phenylethylamine hydrochloride except for a small layer of unchanged acetophenone. 

• Allow the reaction mixture to cool, remove the acetophenone by extraction with four 20 ml portions of toluene (1). 

• Transfer the aqueous acid solution to a 500-ml round-bottomed flask equipped for steam distillation, cautiously add a solution of 6.5g of sodium hydroxide in 125 ml of water, and steam distil; heat the distillation flask so that the volume remains nearly constant. 

• Most of the amine is contained in the first 500 ml of distillate; stop the operation when the distillate is only faintly alkaline. 

• Extract the distillate with five 25 ml portions of toluene, dry the extract with sodium hydroxide pellets and fractionally distil (2). 

• Toluene distils over at 111 °C, followed by the phenylethylamine. 

• Collect the latter as a fraction of b.p. 180-190 °C (the bulk of the product distils at 184-186 °C (3); the yield is 43g (59%).

Notes to keep in mind:

1. The acetophenone may be recovered by washing the toluene solution with dilute alkali, drying with anhydrous calcium sulphate and distilling; the fraction, b.p. 198-205 °C, is collected.

2. Ground glass apparatus must be used as the amine attacks rubber (and cork). Since the product absorbs carbon dioxide from the air, attach the receiving flask to the condenser with a take-off adapter carrying a soda-lime guard-tube.

3. The b.p. under diminished pressure is 80-81 °C/18mmHg. To obtain a very pure sample of the amine, dissolve 1 part (by weight) of the above product in a solution of 1.04 parts of crystallised oxalic acid in 8 parts of hot water, add a little decolourising carbon and filter. The filtered solution deposits crystals of the oxalate salt; about 5g of this salt remains in each 100 ml of mother-liquor, but most can be recovered by evaporation and further crystallisation. The amine may be liberated from its oxalate salt with sodium or potassium hydroxide, steam distillation and purification as described above. The salt provides a convenient method of obtaining a known weight of the amine in water, since it can be weighed out and decomposed with alkali hydroxide.