Reactions of Carboxylic Acids and Their Derivatives- Dehydration (conversion to nitriles):
R-CONH 2 --- P 4 O 10 , heat, (-H 2 O) ---> R-CN91.4.6 Nitriles
- Hydrolysis:
R-CN --- H 3 O+,heat ---> RCOOH
R-CN --- OH-,H 2 O,heat ---> RCOO-- Reduction to aldehyde:
R-CN --- (1) (i-Bu) 2 AlH (2) H 2 O ---> R-COH(i-Bu) 2 AlH = DIBAL-H
- Conversion to ketone (by Grignard or organolithium reagents):
R-CN + R"-M --- (1) Et 2 O (2) H 3 O+---> R-COR”M = MgBr (Grignard reagent) or Li (organolithium reagent)
91.4.7 Mechanisms
A common motif in reactions dealing with carboxylic acid derivatives is the tetrahedral
intermediate. The carbonyl group is highly polar, with the carbon having a low electron
density, and the oxygen having a high electron density. With an acid catalyst, a H+ is
added to the oxygen of the carbonyl group, increasing the positive charge at the carbon
atom. A nucleophile can then attack the carbonyl, creating a tetrahedral intermediate.
For example, in Fischer esterification, the mechanism can be outlined thus: 1) H+ is added
to carbonyl oxygen 2) Oxygen atom of the alcohol adds to the carbonyl carbon 3) Proton
transfer from alcohol oxygen to carboxyl oxygen 4) Water molecule ejected from tetrahedral
intermediate, double bond forms, recreating the carbonyl 5) H+ is removed from carbonyl
oxygen