SYNTHESIS OF HEXANAMIDE

• Place 125 ml of concentrated ammonia solution (d 0.88) in a 600-ml beaker and surround the latter with crushed ice. 

• Stir the ammonia solution mechanically, and introduce 56 g (0.42 mol) of hexanoyl chloride slowly by means of a suitably supported separatory funnel. 

• The rate of addition must be adjusted so that no white fumes are lost. 

• The amide separates immediately. 

• Allow to stand in the ice-water for 15 minutes after all the acid chloride has been introduced. 

• Filter off the amide at the pump; use the filtrate to assist the transfer of any amide remaining in the beaker to the filter (1). 

• Spread the amide on sheets of filter or drying paper to dry in the air. 

• The crude hexanamide (30g, 63%) has m.p. 98-99 °C and is sufficiently pure for conversion into the nitrile (2). 

• Recrystallise a small quantity of the amide by dissolving it in the minimum volume of hot water and allowing the solution to cool; dry on filter paper in the air. 

• Pure hexanamide has m.p. 100 °C.

Notes to keep in mind:

1. The nitrate will deposit small amounts of hexanamide upon concentration to half its original volume.

2. The process is of general application for higher (i.e. > C₅) fatty acids.

Cognate preparation: Isobutyramide (2-methylpropanamide)

• Add 106 g (1 mol) of isobutyryl chloride to 400 ml of concentrated ammonia solution (d 0.88) contained in a 2-litre two-necked flask fitted with a stirrer and dropping funnel, at such a rate that the temperature does not rise above 15 °C. 

• Stir for 1 hour after the addition is complete and attach the flask to a rotary evaporator, connect to a water-jet pump and heat the flask on a boiling water bath until the crystalline deposit is quite dry. 

• Boil the residue with 1200 ml of ethyl acetate, filter the hot solution and extract the residue with further quantities of hot ethyl acetate (2 x 750 ml). 

• Combine the extracts, cool to 0°C and collect the crystals of isobutyramide of m.p. 128-129 °C. The yield after recovery of further crops of crystalline material from the concentrated mother-liquors is 58g (66%).