Addition of HCN
HCN is a very toxic gas, and therefore this is prepared in-situ via the reaction of sulfuric acid with potassium cyanide.
Since HCN is a weak acid, and therefore the concentration of the CN– in solution would be low, reducing the rate of the reaction. In order to avoid this, a base is added which would then shift the equilibrium to the cyanide ion, increasing the rate of the reaction. Acid hydrolysis would then give the alcohol.
The nitrile group can then be oxidised to the carboxylic acid through the process of hydrolysis.
Reduction of aldehydes and ketones
Aldehydes and ketones can be reduced to give alcohols, with the mechanism being the same as a nucleophilic addition, with an H– acting as the nucleophile.
The reducing agents can be either LiAlH4 in ether or NaBH4 which can be used in water.
Fehling’s Test
In this test, the presence of aldehydes but not ketones is detected by reduction of the deep blue solution of copper(II) to a red precipitate of insoluble copper oxide.
The net reaction between an aldehyde and the copper(II) ions in Fehling’s solution may be written as: