Chemistry · Ch 8 — Aldehydes, Ketones and Carboxylic Acids
Reactions Involving –COOH Group
Reactions Involving –COOH Group
These reactions affect the carboxyl group as a whole, rather than just one bond within it.
1. Reduction
The entire group of a carboxylic acid can be reduced all the way to a primary alcohol (), using lithium aluminium hydride () or, better, diborane ():
Diborane is the more selective reagent — it reduces the carboxyl group cleanly without touching other reducible functional groups such as ester, nitro, or halo groups that may be present elsewhere in the molecule. By contrast, sodium borohydride () does not reduce the carboxyl group at all, which is a useful chemoselectivity to remember.
2. Decarboxylation
Heating the sodium salt of a carboxylic acid with soda lime — a mixture of and in a 3 : 1 ratio — expels the carboxyl carbon entirely as carbon dioxide, leaving behind a hydrocarbon with one carbon atom fewer than the parent acid. This loss of is called decarboxylation:
…