nomenclature of nitriles

Reaction type:  Nucleophilic Addition Overview

• Nitriles typically undergo nucleophilic addition to give products that often undergo a further reaction.
• The chemistry of the nitrile functional group, CºN, is very similar to that of the carbonyl, C=O of aldehydes and ketones. Compare the two schemes:

        versus 

• However, it is convenient to describe nitriles as carboxylic acid derivatives because:
• the oxidation state of the C is the same as that of the carboxylic acid derivatives.
• hydrolysis produces the carboxylic acid
• Like the carbonyl containing compounds, nitriles react with nucleophiles via two scenarios:

• Strong nucleophiles (anionic) add directly to the CºN to form an intermediate imine salt that protonates (and often reacts further) on work-up with dilute acid.

            Examples of such nucleophilic systems are :  RMgX, RLi, RCºCM, LiAlH₄
 
• Weaker nucleophiles (neutral) require that the CºN be activated prior to attack of the Nu.

     This can be done using a acid catalyst which protonates on the Lewis basic N and makes the system more electrophilic.

 

            Examples of such nucleophilic systems are :  H₂O, ROH
 


The protonation of a nitrile gives a structure that can be redrawn in another resonance form that reveals the electrophilic character of  the C since it is a carbocation.

Hydrolysis of Nitriles
Reaction type:  Nucleophilic Addition then Nucleophilic Acyl Substitution Summary

• Nitriles, RCºN, can be hydrolyzed to carboxylic acids, RCO₂H via the amide, RCONH₂.
• Reagents : Strong acid (e.g. H₂SO₄) or strong base (e.g. NaOH) / heat.

Related Reactions

• Hydrolysis of Esters and Amides

 

MECHANISM OF THE ACID catalyzed HYDROLYSIS OF NITRILES
Step 1: An acid/base reaction. Since we only have a weak nucleophile so activate the nitrile, protonation makes it more electrophilic.
Step 2: The water O functions as the nucleophile attacking the electrophilic C in the CºN, with the electrons moving towards the positive center.
Step 3: An acid/base reaction. Deprotonate the oxygen that came from the water molecule. The remaining task is a tautomerization at N and O centers.
Step 4: An acid/base reaction. Protonate the N gives us the -NH2 we need....
Step 5: Use the electrons of an adjacent O to neutralise the positive at the N and form the p bond in the C=O.
Step 6: An acid/base reaction. Deprotonation of the oxonium ion reveals the carbonyl in the amide intermediate....halfway to the acid.....