A) Reactions involving cleavage of O – H bond. ) Reactions with metals Carboxylic acid react with active metals like Na, Mg, Zn etc to form corresponding salts with the liberation of hydrogen. Example Acetic acid Sodium acetate OH + 2Na ONa + H CH CH ) Reaction with alkalies Carboxylic acid reacts with alkalies to neutralise them and form salts. XII U12-Carbonyl XII U12-Carbonyl - - - - Example OH + NaOH ONa + H O Accteic acid Sodium acetat e ) Reaction with carbonates and bicarbonates (Test for carboxylic acid group) Carboxylic acids decompose carbonates and bicarbonates evolving carbondioxide gas with effervescence.
Example Acetic acid Sodium acetate OH + Na CO ONa + CO + H O 2CH 2CH ) All Carboxylic acids turn blue litmus red B) Reactions involving cleavage of C-OH bond ) Reactions with PCl , PCl and SOCl The hydroxyl group of carboxylic acids behaves like that of an alcoholic group and is easily replaced by chlorine atom on treating with PCl , PCl or SOCl . Example OH + PCl Cl + POCl + HCl Acetic acid Acetyl Chloride OH + SOCl Cl + SO + HCl C H C H Benzoic acid Benzoyl chloride ) Reactions with alcohols ( Esterification) When carboxylic acids are heated with alcohols in the presence of conc. H SO or dry HCl gas, esters are formed. The reaction is reversible and is called esterification.
Example OH + C H OH OC H + H O C H C H Benzoic acid ethyl benzoate H + XII U12-Carbonyl XII U12-Carbonyl - - - - Mechanism of esterification: The Mechanism of esterification involves the following steps. H C H C C H H C C H H C C H H C C