(b) Addition of sodium hydrogensulphite: Sodium
hydrogensulphite adds to aldehydes and
ketones to form the addition products The position of
the equilibrium
lies largely to
the right hand
side for most
aldehydes and to
the left for most
ketones due to steric reasons The hydrogensulphite addition
compound is water soluble and can be converted back to the
original carbonyl compound by treating it with dilute mineral
acid or alkali Therefore, these are useful for separation and
purification of aldehydes