[emissivity]

hello
I have a question about the reaction 'hydrolysis of nitriles'.
My teacher has told me to study this reaction about acidic basic condition.

I have seen the synthesis of Fenoprofen in the book(Organic chemistry 7th ed, John Mcmurry, thomson, p763)

I've studied that carboxylic acids can be prepared from nitriles by reaction with '''hot aqueous acid''' or base.

Is there any reason NaOH is used?

I think there must be some reasonable reason.

Help me!
I have to find out this problem.. T_T

[Hunter2]

Should be also possible:

http://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CCQQFjAA&url=http%3A%2F%2Fduepublico.uni-duisburg-essen.de%2Fservlets%2FDerivateServlet%2FDerivate-10209%2Ffolie272.pdf&ei=gryfUN6-E8jwsga8s4HgCg&usg=AFQjCNGvCzqnN7_wX3-Zn5F5REKNcN9GRg&cad=rja

[emissivity]

thanks for your comment!

but I precisely want to know why they used NaOH.

professor said all the plant make this pill by this reaction.
not acidic condition.

actually she told us to find out why they do treat this in basic condition.

yield percentage? any danger? is it cheaper?

how can I find this out..

I have no idea... T_T

[discodermolide]

What side products do you get from the basic hydrolysis and the acidic hydrolysis? Will they influence the method of hydrolysis?
Any ideas?

[orgopete]

If I were doing the reaction, I would prefer to do it in acid. However, if you were purifying the product, it would be useful to make the carboxylate to remove it from neutrals. In that case, you may as well use basic conditions as separation can included in the purification.

[emissivity]

I read discondermolide's comment.
I focused on the side product I will get from each reactions.
actually there's no any mechanism explanation about hydrolysis of nitriles in my book.
but I studied the file which hunter2 gave.

after doing that, I saw orgopete's comment about 'purification'

anyway, If I tell you my understanding about the reason the plant choose the basic reaction,
it is because NH3.


hunter2's file taught me that basic condition yields NH3 gas. It goes out easily.
So we can readily purify carboxylates.

but if I treat this reaction in acidic condition,
NH3 reacts with diols
so it needs more reaction to purify it.



Do you think this is right?

anyway If you think that my understanding is right,
thank you for your comments.

thank you all of you

[discodermolide]

Almost correct. Your last statement is not quite right.
There are no diols present, do you mean acids?
Certainly as a part time plant chemist I would always go for the basic hydrolysis unless other factors preclude this.

[emissivity]

I don't know how to indicate that

R-C=OH(+)
   \
   OH

anyway I mean that

if I treat this in acidic condition,

it yields mixture which contains carboxylic acid and NH4(+)

So It needs more step to purify this mixture.

therefore, the plant do in basic condition rather than acidic condition.

[discodermolide]

The acidic hydrolysis of nitriles yield carboxylic acids as their ammonium salts as you say. The ammonia produced also neutralises the acid, causing the concentration to drop.
Using base provides the salt of the acid, thus making it easier to purify. Adding acid then generates the free carboxylic acid, hopefully pure.

[emissivity]

thank you so much

your comment is really really helpful

thank you

[orgopete]

The acidic hydrolysis of nitriles yield carboxylic acids as their ammonium salts as you say. The ammonia produced also neutralises the acid, causing the concentration to drop.
Using base provides the salt of the acid, thus making it easier to purify. Adding acid then generates the free carboxylic acid, hopefully pure.

That is just wrong.

RCN + H2O + HCl  RCO2H + NH4Cl (water soluble)

No carboxylate.

Because an amide (intermediate) is more basic than a nitrile, it is difficult to stop an acid catalyzed hydrolysis at the amide stage. It will go all the way to the acid. In this instance, the acid is a solid and likely will precipitate from the reaction mixture. The nitrile is likely also a solid, so it may be more difficult to visually determine reaction completeness or mutual solubility may hamper reaction completeness in a completely aqueous system.

If the hydrolysis is performed under basic conditions, you should end up with a water soluble carboxylate salt. The ammonia is also water soluble and depending upon heat and concentration will be largely in the water layer. It poses not problem. The reason I am more hesitant of using basic conditions is a dianion intermediate is required to eject ammonia. This requires a greater excess of base and more vigorous conditions. Filtration or extraction can remove neutral impurities without adjusting the pH. Acidification will convert ammonia into a water soluble ammonium salt and precipitate the carboxylic acid.

If neutral impurities must be removed by forming a water soluble carboxylate salt, the basic hydrolysis will have one fewer steps. Solubility may determine the route. Under basic conditions, the reaction may be completed without an organic cosolvent,  just water. Under acidic conditions, an organic cosolvent may be needed to drive the reaction to completion. This will add to raw material and environmental costs.

[fledarmus]

I would certainly avoid adding an acid to any reaction mixture which might contain some leftover NaCN, especially on a large scale. That looks like an accident waiting to happen.

[orgopete]

Fledarmus's explanation seems the most plausible. For any commercial process, if two steps can be performed as one will improve efficiency. Since the benzyl bromide is the most expensive piece, an excess of cyanide may have been used to improve rate and productivity. Basic hydrolysis would be more compatible with excess cyanide (though I don't know that it would be a problem in a process route), removal of neutral impurities, and fewest steps.