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Topic: Can HCl be used for the hydrolysis of nitriles?  (Read 5625 times)

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Offline NewtoAtoms

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Can HCl be used for the hydrolysis of nitriles?
« on: March 18, 2009, 10:33:46 PM »
Hello Organic Chemists.

My basic question is:

Generally H2SO4 is used for the hydrolysis of R-nitriles (according to my textbook) and HCl for the hydrolysis of nitrile groups in cyanohydrins... HOWEVER can HCl also be used for the hydrolysis of R-nitriles????

What I mean by this all is:

For the synthesis of carboxylic acids by the preparation and hydrolysis of nitriles, in my text it always shows:

STEP #1

Primary or secondary alkyl halide + cyanide ion ----------> nitrile

STEP #2

Nitrile -----H20, H2SO4, heat-----> carboxylic acid.

I also know that nitrile groups in cyanohydrins are hydrolyzed under similar conditions, FOR EXAMPLE:

2-pentanone ---NaCN, H+--->2-pentanone cyanohydrin ---H20, HCl, heat ----> 2-hyroxy-2-methyl-pentanoic acid.





Offline russellm72

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Re: Can HCl be used for the hydrolysis of nitriles?
« Reply #1 on: March 19, 2009, 05:56:21 AM »
Hello again,

Again I often use [14C] KCN and label organic compounds. Normally the nitrile is hydrolysed to the acid with 6N HCl at reflux so the answer to your question is yes.

Don't get to regimented by what text books say. Not all compounds containing a nitrile will behave in a similar fashion.

R.

Offline Squirmy

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Re: Can HCl be used for the hydrolysis of nitriles?
« Reply #2 on: March 19, 2009, 09:12:02 PM »
I agree, but think it's worth pointing out that it often does matter what acid you use.

The best example I can think of is dehydration of an alcohol to give an alkene. The counter ions (Chloride vs. sulfate) differ in their nucleophilicity and leaving group ability. HCl will likely give some substitution product rather than elimination. Also, sulfuric acid is a much better dehydrating agent than HCl...its reaction with water is much more exothermic, so this helps drive the reaction toward the alkene. In short, replacing H2SO4 with HCl would be a bad idea for such a reaction.

In your case, you're adding water to the molecule, so there should be plenty of water around and the acid's ability to dehydrate isn't important. As for chloride acting as a nucleophile, I'm sure it still does, but it doesn't lead to product. If chloride adds as a nucleophile, it will get kicked back out because it's the best leaving group. Even if it stayed (very doubtful), it would give an acid chloride that would hydrolyze much more easily than the nitrile. So, here it shouldn't matter which acid you use.

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