Reaction L.— a Addition of Hydrogen Cyanide to Aldehydes or Ketones

Reaction L. (a) Addition of Hydrogen Cyanide to Aldehydes or Ketones. 

Nascent hydrogen cyanide formed by the action of hydrochloric acid on potassium cyanide is usually employed except with sugars, where hydrocyanic acid and a little ammonia are used. The manner in which ammonia promotes the action, and the better results obtained by the use of the bisulphite compound of the aldehydes and potassium cyanide, have been dealt with under Reaction XXXVIII. (c). 

Preparation 64 illustrates the importance of this reaction in the sugar group. Eor the hydrolysis of nitriles, see p. 239. 

10 gins. (1 mol.) of acetone are shaken with a saturated sodium bisulphite solution containing 18 gms. (1 mol.) of NaHS03, and, after cooling, 30 gms. (excess) of a cold 50% solution of 96% potassium cyanide are slowly added. The crystalline bisulphite compound soon dissolves and a fluorescent oil is formed. This is extracted several times with ether, and the ethereal extracts are shaken with saturated bisulphite solution (to remove acetone) and then washed with saturated brine. The ether is removed on a water bath, and the residual oil dried under reduced pressure over cone, sulphuric acid. It is then fractionated under reduced pressure, the fraction 80°—85° at 23 mms. being retained. 

The action of hydrogen cyanide on the aldehyde itself, and the action of potassium cyanide on the bisulphite compound, are directly contrasted in the following preparation. 

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