Organic Chemistry: Carboxylic Acids

Overview

Carboxylic acids are a significant group of organic compounds found in a variety of everyday substances such as vinegar and some fruits.
The name ‘carboxylic acid’ originates from the presence of a carboxyl group (-COOH) in the molecule.
The simplest carboxylic acid is methanoic acid (HCOOH), which is the formic acid found in the sting of red ants.

Structural Properties

The central structure of a carboxylic acid has a carbon atom bonded to an oxygen atom by a double bond, and to a hydroxyl group by a single bond.
It’s the carboxyl group (-COOH) that gives carboxylic acids their acidic properties.
Carboxylic acids usually have higher melting and boiling points than similar-sized alcohols or aldehydes because of the existence of dimerisation, where two carboxylic acid molecules form dimers (pairs), increasing stability and boiling point.

Common and Systematic Names

Carboxylic acids are commonly named by adding ‘-ic’ to the root of the alkane chain in the acid and adding ‘acid’ at the end.
For example, CH3COOH is known as ethanoic acid in IUPAC nomenclature, but can also be commonly named as acetic acid.
Propanoic acid and butanoic acid are other examples of carboxylic acids, corresponding to the alkanes propane and butane, respectively.

Physical Properties

Carboxylic acids are polar molecules due to the presence of the carboxyl group, which can form hydrogen bonds with other molecules.
These strong intermolecular forces make carboxylic acids have a high boiling point compared to molecules of similar size that do not form hydrogen bonds.
They are generally liquids at room temperature, and many have distinct odours.

Chemical Reactions

Carboxylic acids exhibit typical acid properties, such as ability to neutralise bases to form salts, and react with carbonates to release carbon dioxide.
They also involve in esterification reactions, where they react with alcohols to form esters and water.
Heating carboxylic acids with alcohols in the presence of a strong acid catalyst (like concentrated sulphuric acid) can result in an esterification reaction.

Uses of Carboxylic Acids

Carboxylic acids have wide applications in industries. They are used for making soaps, detergents, plasticisers, and in the textile industry for dying process.
They also find applications in the food industry, where they’re used as vinegar (acetic acid) and as food preservatives.
In pharmaceutical industry, they’re employed in making various medications, and in chemical industry for producing polymers and resins.