SYNTHESIS OF BENZYLAMINE

A-Benzylphthalimide:

• Grind together 76g (0.55 mol) of finely powdered, anhydrous potassium carbonate and 147g (1 mol) of phthalimide in a glass mortar, transfer the mixture to a round-bottomed flask and treat it with 151g (1.2 mol) of redistilled benzyl chloride. 

• Heat in an oil bath at 190 °C under a reflux condenser for 3 hours. 

• While the mixture is still hot, remove the excess of benzyl chloride by steam distillation. 

• The benzylphthalimide commences to crystallise near the end of the steam distillation. 

• At this point, cool the mixture rapidly with vigorous swirling so that the solid is obtained in a fine state of division. 

• Filter the solid with suction on a Buchner funnel, wash well with water and drain as completely as possible; then wash once with 200 ml of 60 per cent ethanol and drain again. 

• The yield of crude product, m.p. 100-110 °C, is 180g (76%). Recrystallise from glacial acetic acid to obtain pure benzylphthalimide, m.p. 116°C: the recovery is about 80 per cent.

Benzylamine:

• Warm an alcoholic suspension of 118.5g (0.5 mol) of finely powdered benzylphthalimide with 25g (0.5 mol) of 100 per cent hydrazine hydrate (CAUTION: corrosive liquid): a white, gelatinous precipitate is produced rapidly. 

• Decompose the latter (when its formation appears complete) by heating with excess of hydrochloric acid on a steam bath. 

• Collect the phthalylhydrazide which separates by suction filtration, and wash it with a little water. 

• Concentrate the filtrate by distillation on a rotary evaporator to remove alcohol, cool, filter from the small amount of precipitated phthalylhydrazide, render alkaline with excess of sodium hydroxide solution and extract the liberated benzylamine with ether. 

• Dry the ethereal solution with potassium hydroxide pellets, remove the solvent (rotary evaporator) and finally distil the residue. Collect the benzylamine at 185-187 °C: the yield is 50g (94%).

Cognate preparation: 2-Phenylethylamine

• Prepare 2-phenylethylphthalimide as above by substituting 2-phenylethyl bromide for benzyl chloride: recrystallise the crude product from glacial acetic acid; m.p. 131- 132°C. 

• Convert it into 2-phenylethylamine by treatment with hydrazine hydrate and hydrochloric acid as described for benzylamine. The yield of 2-phenylethylamine, b.p. 200-205 °C, is about 95 per cent.