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 (c) Addition of Grignard reagents:   (refer Unit 7, Class XII) (d) Addition of alcohols:  Aldehydes react with one equivalent of
monohydric alcohol in the presence of dry hydrogen chloride
to yield alkoxyalcohol intermediate, known as hemiacetals,
which further react with one more molecule of alcohol to
give a gem-dialkoxy
compound known as
acetal as shown in the
reaction