SYNTHESIS OF PHENYLACETAMIDE

• In a 2-litre three-necked flask, provided with a thermometer, reflux condenser and efficient mechanical stirrer, place 100g (98 ml, 0.85 mol) of benzyl cyanide and 400 ml of concentrated hydrochloric acid. Immerse the flask in a water bath at 40 °C and stir the mixture vigorously: the benzyl cyanide passes into solution within 20-40 minutes and the temperature of the reaction mixture rises to about 50 °C. 

• Continue the stirring for an additional 20-30 minutes after the mixture is homogeneous. 

• Replace the warm water in the bath by tap water at 15°C, replace the thermometer by a dropping funnel charged with 400 ml of cold distilled water and add the latter with stirring: crystals commence to separate after about 50-75 ml have been introduced. 

• When all the water has been run in, cool the mixture externally with ice-water for 30 minutes (1), and collect the crude phenylacetamide by filtration at the pump. 

• Remove traces of phenylacetic acid by stirring the wet solid for about 30 minutes with two 50 ml portions of cold water; dry the crystals at 50-80 °C. 

• The yield of phenylacetamide, m.p. 154-155 °C, is 95 g (82%). Recrystallisation from rectified spirit raises the m.p. to 156 °C.

Notes to keep in mind:

1.  The suspension of phenylacetamide may be further hydrolysed to phenylacetic acid by refluxing with stirring until the solid dissolves. The mixture becomes turbid after 30 minutes and the product begins to separate as an oil: refluxing is continued for 6 hours, the mixture is cooled first with tap water and then by an ice-water bath for about 4 hours. The crude phenylacetic acid is filtered at the pump, washed with two 50 ml portions of cold water and dried in a desiccator. The resulting crude acid melts at 69-70 °C; it may be purified by recrystallisation from light petroleum (b.p. 40-60 °C) or, better, by vacuum distillation.