Download Carboxylic Acid Derivatives: Amides

The ammonium salt formation is reversible.
Upon heating, a slower but thermodynamically more favorable reaction between
the carboxylic acid and the amine takes place.
Dicarboxylic acids react with amines to give imides.
Imides, or the nitrogen analogs of cyclic anhydrides, can be formed through the
reaction of a dicarboxylic acid and ammonia or a primary amine.
Amino acids cyclize to lactams.
Some amino acids can undergo an intramolecular cyclization to the corresponding
cyclic amide, or lactam.
The penicillin class of antibodies derives its biological activity from a lactam
function.
19-11 Reduction of Carboxylic Acids by Lithium Aluminum
Hydride
Carboxylic acids are converted to their corresponding primary alcohols by
reduction with LiAlH4.
19-12 Bromination Next to the Carboxy Group: the
Hell-Volhard-Zelinsky Reaction
Monobromination of alkanoic acids at the -carbon can be accomplished by
treatment with Br2 in the presence of catalytic amounts of PBr3.
The PBr3 is usually generated in situ by adding a little red phosphorous to the
starting materials, which is then converted into PBr3 by the bromine present.
Halogenation at the -carbon of a carboxylic acid is a useful intermediate in the
synthesis of 2-hydroxy- and 2-amino acids.
19-13 Biological Activity of Carboxylic Acids
Fatty acids are derived from the coupling of acetic acid.
Acetic acid is the primary building block for the biosynthesis of more naturally
occurring compounds than any other single precursor substance.
The substance 3-methyl-3-butenyl pyrophosphate is the crucial intermediate in
the synthesis of terpenes:
Fats are esters of long-chain carboxylic acids.
Hydrolysis of fats, or saponification, yields the corresponding fatty acids.
The most important fatty acids are between 12 and 22 carbons long and may
contain cis carbon-carbon double bonds.
Most fatty acids contain an even number of carbon atoms since they are derived
directly from the polymerization of acetic acid units.
Reduction of the ketone to a
methylene follows. The
resulting acid replaces the
acetic acid in step 1 and the
process repeats until the
carbon chain is 16 carbons
long.
Arachidonic acid is a biologically important unsaturated fatty acid.
Arachidonic acid is an essential fatty acid which is enzymatically converted into
many important biological molecules:
Nature also produces complex polycyclic carboxylic acids.
Many complex, biologically active natural products contain carboxylic acid groups.
The carboxylic acid may not contribute directly to the biological activity, but may:
•Confer water solubility
•Allow for salt formation or ion transport
•Enable micellar-type aggregation