Carboxylic acids are very important organic compounds. They contain carboxyl functional group(-COOH). The carboxyl name has been derived from carbonyl(-CO) and hydroxyl(-OH). Carboxylic acids may be aliphatic or aromatic on the basis of the group alkyl or aryl attached to the carbon atom of the carboxyl group.
Fatty acids : Aliphatic carboxylic acids from C12 to C18 are called fatty acids.
Nomenclature : I. Common names :
- To get common names of carboxylic acids, we add a suffix -ic acid in the names obtained by Greek or Latin words for their natural sources. Ex : HCOOH is called formic acid because it was first obtained from red ants and the latin word for ants is formica. Some more examples are : CH3COOH – Acetic Acid/ C3H7COOH-Butyric Acid
II. IUPAC names :
- In IUPAC system, we replace -e by -oic acid at the end of an alkane for aliphatic carboxylic acids.
- The numbering is started from the carboxylic carbon in the parent chain.
- To name a carboxylic acid having more than one carboxyl group -e of alkane is retained at the end and the number of carboxyl groups is expressed by prefixes like di, tri, tetra etc.
- The position of -COOH group is indicated by numerals 1,2,3…
Structure of the carboxyl group : The bonds to the carboxyl carbon in a carboxylic acid are coplanar. The angle between the bonds is 1200. The resonance structures of the carboxyl group is as follows:
Preparation of carboxylic acids :
1.From primary alcohols : When primary alcohols are oxidised by KMnO4 in neutral, acidic or alkaline medium or K2Cr2O7 and CrO3 in acidic, carboxylic acids are produced. Ex :
2.From primary aldehydes : When aldehydes are oxidised by mild oxidising agents, they give carboxylic acids.
3.From alkylbenzenes : Alkylbenzenes give aromatic carboxylic acids on oxidation by chromic acid or acidic or alkaline KMnO4. But, only primary and secondary alkyl groups are oxidised by this manner. Tertiary groups are not affected.