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

Explanation

(i) Acetylation refers to the process of introducing an acetly group into a compound namely, the substitution of an acetyl group for an active hydrogen atom. Acetylation is usually carried out in presence of a base such as pyridine, dimethylanitine, etc.
`CH_(3)COCl+CH_(3)CH_(2)OHoverset("Pyridine")rarrCH_(3)COOC_(2)H_(5)+HCl`
(ii) Cannizzaro reaction : Aldehydes which do not contain an a-hydrogen atom, when treated with concentrated alkali solution undergo disproportionation, i.e., self oxidation reduction. As a result, one molecule of the aldehyde is reduced to the corresponding alcohol at the cost of the other which is oxidised to the corresponding carboxylic acid. This reaction is called Cannizzaro reation.
e.g., `2H-overset(O)overset(||)C-H+underset((50%))(NaOH)rarrCH_(3)-OH+H-overset(O)overset(||)C-ONa`
(iii) Cross aldol condensation: Aldol condensation between two different aldehydes is called cross aldo condensation. If both aldehydes contain a-hydrogens, It gives a mixture of four products.
`CH_(3)-overset(O)overset(||)C-H+H-overset(O)overset(||)C-Hoverset("Dil. NAOH")rarrHO-CH_(2)-CH_(2)-overset(O)overset(||)C-H`
(iv) Decarboxylation: The process of removal of a molecule of `CO_(2)` from a carboxylic acid is called decarboxylation. Sodium salts of carboxylic acids when heated with soda-lime undergoes decarboxylation to yield alkanes.
`CH_(3)CH_(2)COONa+NaOHoverset(CaO,630 K)rarrCH_(3)-CH_(3)+Na_(2)CO_(3)`