Describe the following
i. Acetylation
ii. Cannizzaro reaction
iii. Cross aldol condensation
iv. Decarboxylation

Explanation

(I ) acetylation
the replacement of an active hydrogen of alcohols , phenols or amines with acetyl group group to form corresponding esters or amides is called acetylation . It is carried out by using acid chlorides or anhydries in the presence of a base such as pyridine , dimethyl aniline , etc , for example ,
` underset("Acetyl chloride ") (CH_3 COCI) + underset("Ethyl alcohol ") ( CG_3 CH_2 OH ) overset("Pyridine ") to underset("Ethyl acetate ")(CH_3 COOC_2 H_5) +HCI`
` underset("Acetic anhydride ")(CH_3 CO_2 O ) + underset("phenol ") (C_6 H_5 OH) to underset("phenyl acetate ") (CH_3 COOC_6 H_5 ) + CH_3 COOH`
(ii ) Cannizzaro.s reaction
aldehydes which do not contain any ` alpha -` hydrogen atom ( e.g benzaldehyde , formaldehyde ) undergo self oxidation and reduction reaction on treatment with conc. solution of caustic alkali . in this reaction one molecule is oxidised to acid while another molecular is reduced to alcohol
`underset("formaldehyde ") (HCHO + HCHO ) overset(50 % NaOH ) to underset(" methyl alcohol ") (CH_3 OH) + underset(" sodium formate ") (HCOO^(-)Na^+) `

(iii ) cross aldol condensation
The condensation of two different molecules of aldehydes or ketons is called cross aldol condensation . it is useful synthetic reaction only if one of hte aldehydes does not contain ` alpha ` - hydrogen atoms i.e, formaldehyde , benzaldehyde , etc .

( iv ) Decarboxylation
The process of removal of a molecule of `CO_2` from a carboxylic acid is called decarboxlation . it is usually carried out by heating a mixture of a carboxylic acid or its sodium salt with sode lime `(NaOH +CaO )`.