(i) Acetylation

The introduction of an acetyl functional group into an organic compound is known as acetylation.
It is usually carried out in the presence of a base such as a pyridine. This process involves the substitution of an acetyl group for an active hydrogen atom.

Acetyl chloride and acetic anhydride are commonly used as acetylating agents.
For example, acetylation of ethanol produces ethyl acetate. The reaction is as follows:

(ii) Cannizzaro reaction:

The self oxidation-reduction (disproportionation) reaction of aldehydes having no α-hydrogen on treatment with concentrated alkalis is known as the Cannizzaro reaction.

In this reaction, two molecules of aldehydes participate where one is reduced to alcohol and the other is oxidized to a carboxylate ion.

For example, when benzaldehyde is treated with concentrated potassium hydroxide, then benzyl alcohol and potassium benzoate are obtained as a product. 

The reaction is as follows:

(iii) Cross-aldol condensation:

When aldol condensation is carried out between two different aldehydes, or two different ketones, or an aldehyde and a ketone, then the reaction is called a cross-aldol condensation. If both the reactants contain α-hydrogens, four compounds are obtained as products.
For example, ethanal and propanal react to give four different products. 

The reactions are as follows: 

(iv) Decarboxylation:
Decarboxylation refers to the reaction in which carboxylic acids lose carbon dioxide to form hydrocarbons when their sodium salts are heated with soda-lime. The reaction is as follows:

Decarboxylation also takes place when aqueous solutions of alkali metal salts of carboxylic acids are electrolyzed. This electrolytic process is known as Kolbe’s electrolysis.