A nitrile is any organic compound that has a -C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile butadiene rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Organic compounds containing multiple nitrile groups are known as cyanocarbons.
Inorganic compounds containing the -C≡N group are not called nitriles, but cyanides instead.Though both nitriles and cyanides can be derived from cyanide salts, most nitriles are not nearly as toxic.
HYDROLYSING NITRILES This page looks at the hydrolysis of nitriles under either acidic or alkaline conditions to make carboxylic acids or their salts.
The hydrolysis of nitriles Introduction
When nitriles are hydrolysed you can think of them reacting with water in two stages - first to produce an amide, and then the ammonium salt of a carboxylic acid.
For example, ethanenitrile would end up as ammonium ethanoate going via ethanamide.
In practice, the reaction between nitriles and water would be so slow as to be completely negligible. The nitrile is instead heated with either a dilute acid such as dilute hydrochloric acid, or with an alkali such as sodium hydroxide solution.
The end result is similar in all the cases, but the exact nature of the final product varies depending on the conditions you use for the reaction.
Acidic hydrolysis of nitriles
The nitrile is heated under reflux with dilute hydrochloric acid. Instead of getting an ammonium salt as you would do if the reaction only involved water, you produce the free carboxylic acid.
For example, with ethanenitrile and hydrochloric acid you would get ethanoic acid and ammonium chloride.
Why is the free acid formed rather than the ammonium salt? The ethanoate ions in the ammonium ethanoate react with hydrogen ions from the hydrochloric acid to produce ethanoic acid. Ethanoic acid is only a weak acid and so once it has got the hydrogen ion, it tends to hang on to it.
Alkaline hydrolysis of nitriles
The nitrile is heated under reflux with sodium hydroxide solution. This time, instead of getting an ammonium salt as you would do if the reaction only involved water, you get the sodium salt. Ammonia gas is given off as well.
For example, with ethanenitrile and sodium hydroxide solution you would get sodium ethanoate and ammonia.
The ammonia is formed from reaction between ammonium ions and hydroxide ions.
If you wanted the free carboxylic acid in this case, you would have to acidify the final solution with a strong acid such as dilute hydrochloric acid or dilute sulphuric acid. The ethanoate ion in the sodium ethanoate will react with hydrogen ions as mentioned above.
Nitrile oxides
Nitrile oxides have the general structure R-CNO.
Do you know about The Reactions of RLi or RMgX with Nitriles? I have find the reaction, but i don’t find about the mechanism maybe you can explain to me about it’s mechanism? Thank’s
BalasHapusReactions of RLi or RMgX with Nitriles
HapusReaction usually in Et2O or THF
Reaction type: Nucleophilic Acyl Substitution then Nucleophilic Addition
Summary:
• Nitriles, RCN, react with Grignard reagents or organolithium reagents to give ketones.
• The strongly nucleophilic organometallic reagents add to the CN bond in a similar fashion to that seen for aldehydes and ketones.
• The reaction proceeds via an imine salt intermediate that is then hydrolysed to give the ketone product.
• Since the ketone is not formed until after the addition of water, the organometallic reagent does not get the opportunity to react with the ketone product.
• Nitriles are less reactive than aldehydes and ketones.
• The mechanism is an example of the reactive system type.
MECHANISM FOR THE REACTION OF RMgX WITH AN NITRILE
Step 1:
The nucleophilic C in the organometallic reagent adds to the electrophilic C in the polar nitrile group. Electrons from the CN move to the electronegative N creating an intermediate imine salt complex.
Step 2:
An acid/base reaction. On addition of aqueous acid, the intermediate salt protonates giving the imine.
Step 3:
An acid/base reaction. Imines undergo nucleophilic addition, but require activation by protonation (i.e. acid catalysis).
Step 4:
Now the nucleophilic O of a water molecule attacks the electrophilic C with thebond breaking to neutralise the change on the N.
Step 5:
An acid/base reaction. Deprotonate the O from the water molecule to neutralise the positive charge.
Step 6:
An acid/base reaction. Before the N system leaves, it needs to be made into a better leaving group by protonation.
Step 7:
Use the electrons on the O in order to push out the N leaving group, a neutral molecule of ammonia.
Step 8:
An acid/base reaction. Deprotonation reveals the carbonyl group of the ketone product.
do you know about The Reactions of RLi or RMgX with Nitriles? I have find the reaction but i don’t find about the mechanism maybe you can explain to me about it’smechanism? Thank’s
BalasHapusdo you know about The Reactions of RLi or RMgX with Nitriles, I have find the reaction.but i don’t find about the mechanism maybe you can explain to me about it’smechanism? Thank’s
BalasHapusi like your article, lina.. that let me know further information about nitriles.
BalasHapusBut, I still have a question. If we see the hydrolysis of nitriles, both in acidic and alkaline condition we need the heating process. Could you explain me why does we need it, and is it possible if we do the hydrolysis without heating process ?
I like the article you posted, lina.. that let me know further information about nitriles.
BalasHapusBut, I still have question. If we see the hydrolysis, both in acidic and alkaline condition we need the heating process. Could you explain me why do we need it, and is it possible to do the hydrolysis without heating process ?
I like the article you posted, lina.. that let me know further information about nitriles.
BalasHapusBut, I still have question. If we see the hydrolysis, both in acidic and alkaline condition we need the heating process. Could you explain me why do we need it, and is it possible to do the hydrolysis without heating process ?
Good posted Lina, but after i read this I want to ask Why is the free acid formed rather than the ammonium salt?
BalasHapus