Nomenclature
Carboxylic acids are named by changing the ending -ano to -oic. The longest chain containing the carboxyl group is taken as the main chain and is numbered starting from this group.
Physical Properties
They have high melting and boiling points. Due to hydrogen bonding, the molecules join in pairs forming dimers.
Acidity and Basicity
Carboxylic acids are characterized by the significant acidity of the hydrogen on the hydroxyl group. They can also behave as bases, protonating on the carbonyl group.
Synthesis Methods
Carboxylic acids are obtained by hydrolysis of nitriles, reaction of organometallics with CO2, and oxidation of primary alcohols.
Synthesis of Acyl Halides
Acid halides are obtained by the reaction of carboxylic acids with phosphorus tribromide or phosphorus oxychloride.
Synthesis of Anhydrides from Carboxylic Acids
The condensation of carboxylic acids or better carboxylates with acyl halides produces anhydrides.
Synthesis of Esters from Acids
The reaction of carboxylic acids with alcohols in an acidic medium transforms them into esters, an important reaction known as esterification.
Synthesis of Amides
Amides are obtained by the reaction of acids and amines. The process is carried out by heating to 150ºC and in the absence of acid.
Reaction with Organometallic Reagents
Organolithics react with carboxylic acids forming ketones. Lithium aluminium hydride reduces them to alcohols.
Reduction of Carboxylic Acids
Lithium aluminium hydride reduces carboxylic acids to alcohols. The reaction proceeds in two stages:
- deprotonation of the acidic hydrogen.
- nucleophilic attack of the reductant on the carbonyl.
Acid Enolates
Similarly to aldehydes and ketones, carboxylic acids also form enolates by losing an α hydrogen. Carboxylic acid enolates are good nucleophiles and undergo alkylation reactions, epoxide opening, attack on carbonyls, etc.
Hell-Volhard-Zelinsky Reaction
The halogenation at the α position is carried out with Br2/PBr3.
Hunsdiecker Reaction
Carboxylic acids decarboxylate by losing carbon dioxide to generate haloalkanes.