(a) Giving a chemical equation for each, illustrate the following processes :
(i) Cannizzaro reaction
(ii) Acetlyation
(iii) Decarboxylation
(b) State chemical tests to distinguish between the following pairs of compounds. :
(i) Propanal and Propanone
(ii)Phenol and Benzoic acid

Explanation

(a) (i) Cannizzaro reaction : Aldehydes which do not certain any a-hydrogen atom such as formaldeyde HCHO and benzaldehyde `C_(6)H_(5)CHO` undergo self oxidation and reduction reaction on treatment with concentrated alkali. A mixture of an alcohol and a slat of a carboxylic acid is formed.
`underset("Methanal")(HCHO)+HCHOoverset(NaOH)tounderset("Methanol")(CH_(3)OH)+underset("Sod. formate")(H COONa)`
`underset("Benzeldehyde")(C_(6)H_(5)CHO)+underset("Benzyl alcohol")(C_(6)H_(5)CHO)overset(NaOH)tounderset("Ethyl aetate")(CH_(3)COOC_(2))H_(5)+CHl` ltbr (ii) Acetylation : The replacement of an active hydrogen of alcohols, phenols or amines with an acyl group to form the correcponding esters or amides is called acylation
`underset("Acetyl chloride")(CH_(3)COCl)+underset("Ethyl alcohol")(CH_(3)CH_(2)OH)overset("Pyridine")rarrunderset("Ethuyl acetate")(CH_(3)COOC_(2)H_(5))HCl`
(iii) Decarboxylation : The process of removal of molecule of `CO_(2)` from a carboxylic acid is called decarboxylation It is carried out by heating a carboxyli acid with soda-lime (Na OH+CaO) at 360 K

(b) (i) Fehiling solution test : Warm each compouond with few drops of Fehiling solution. Propanl gives a red precipate of curposes oxide
`CH_(2)CH_(2)CHO+underset("Fehling solution")ubrace(Cu^(2+)+5OH^(-))toCH_(3)CH_(2)COOBa+underset("red ppt")(Cu_(2)O)+3H_(2)O`
Propanoen does give this test
(ii) Add sodium bicarbonate to each compound
With benzoic acid, `CO_(2)`, gas is evolved.