Reactions and characterisation of aliphatic cyanides nitriles

Aliphatic nitriles are usually liquids or low melting point solids. The most important reaction of a nitrile is its hydrolysis either by an alkali or by an acid to the corresponding aliphatic acid characterisation of the acid enables the identity of the original nitrile to be established. 

The excess of alkali is then neutralised with dilute hydrochloric acid (phenolphthalein) and the solution is evaporated to dryness on the water bath. The acid may then be characterised as the S-benzyl-wo-thiuronium salt or as the pbromophenacyl ester (Section 111,85). In many instances the derivative may be prepared directly from the neutralised solution. 

The acid, if monobasic, can usually be distilled directly from the reaction mixture. If this procedure is not possible, the reaction mixture is poured into excess of crushed ice, and the acid is isolated by ether extraction or by other suitable means. The acid is then characterised (Section 111,85). The addition of hydrochloric acid (as sodium chloride say 5 per cent, of the weight of sulphuric acid) increases the rate of the reaction. 

For those nitriles which yield water-insoluble amides (e.g., the higher alkyl cyanides), hydrolysis to the amide often leads to a satisfactory derivative. The hydration is effected by warming a solution of the nitrile in concentrated sulphuric acid for a few minutes, cooling and pouring 

Warm a solution of 0 5 g. of the nitrile in 2 ml. of concentrated sulphuric acid to 80-90° and allow the solution to stand for 5 minutes. Cool under the tap and pour the sulphuric acid solution into 20 ml. of cold water. Filter off the precipitated solid and stir it with 5 ml. of cold 5 per cent, sodium hydroxide solution. Collect the insoluble crude amide and recrystallise it from dilute alcohol. 

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