[vhpk]

Hi everyone,
I have a question regarding the product of the nucleophilic attack of CN^- towards carbonyl compound.
The catalyst ( acid or base) could be used to enhance the reaction, and the final product is cyanohydrin. I wonder at this point. The reaction could go further, couldn't it? In the acidic solution, the final product is carboxylic acid and ammonium ion, in basic solution, it would be carboxylate and ammonia.
So will the reaction go on or stop at the cyanohydrin formation stage ?
Thank you very much.

[stewie griffin]

You get the cyanohydrin. Now which part of the molecule are you saying could possibly get converted to the acid? Are you referring to the alcohol part of the cyanohydrin or the cyano part of the cyanohydrin? The alcohol part isn't going to do anything (except possibly eliminate if the reaction conditions were too extreme). The cyano group can be converted to a carboxylic acid by either acid or base (as you say), however the conditions required to achieve that transformation are far more harsh (strong acid or strong base, usually reflux for hours to days) than the conditions needed to simply add cyanide anion into an aldehyde.
Therefore I would say that if your goal is to make the cyanohydrin, then no I wouldn't be concerned about accidentally converting the cyano group to an acid b/c in the lab you would control the reaction conditions and easily stop at the cyanohyrdin. If you actually wanted to the acid, I suppose you could try to make that too by trying stronger base and higher reaction temperatures.

[srihari]

thank you for the answer

and btw I am not at all conversant with the experimental aspect of the reactions , have been studying the theoretical aspect for quite a while .
Could you please suggest some ways to get started in the experimental aspects ? I am a first year student and hardly any prof is allowing me access to his/her lab . So just to be prepared when the time is right , I'd like learn the practical considerations , any book suggestions , please .

Regards
Srihari

[stewie griffin]

Well obviously the best way to learn is to be in the lab where others can pass down their knowledge and you can learn hands on. But if you are unable to get into a research lab yet (not surprised, most profs want you to have taken several labs before they accept you so keep at it) and are looking to get prepared for research you could check out "Advanced Practical Organic Chemistry" by J. Leonard, B. Lygo, and G. Procter. It has a great intro to doing organic reactions, purification, techniques, etc. Also, simply start reading the literature. I would suggest looking at some total synthesis papers, note what reactions look interesting/new to you, then look at the experimental to see what they did (did they heat it, hit it with light, how long does this type of reaction take, etc).

[vhpk]

Thank you very much 

[srihari]

Thank you

[orgopete]

I do not agree that hydrolysis of a cyanohydrin occurs under conditions of their formation. If the reaction is carried out under strongly basic conditions, one is more likely to find aldol condensation or other base catalyzed reactions. If the reaction is carried out under strongly acidic conditions, cyanide addition will be slowed or stopped.

An example of their formation is described here:
http://orgo.curvedarrow.com/punbb/viewtopic.php?id=321

One of my favorite sources for reaction conditions is Organic Synthesis and it is available online.

[stewie griffin]

Glad to see that orgopete agrees with me when I say that hydrolysis of the cyano group to an acid would not be a problem when trying to make a cyanohydrin. 
Orgopete makes a good point though. I wasn't thinking when I said that one could attempt cyanide addition and conversion to the acid with strong base/heat. Indeed you would enolize the starting ketone or aldehyde.
However, I see no reason why you can't do it under acidic conditions in one pot. Start with mild acid to get the cyanohydrin formation, then add stronger acid to convert to the acid. I've never tried this in the lab so I can't say if it will work or not, but I think the reasoning seems ok. If someone has tried this perhaps they can comment?

[orgopete]

Two points. You cannot hydrolyze the cyanohydrin with base because it reverses to give a carbonyl compound and cyanide.

I agree that one could probably do the reaction in one pot. Because the final product is a carboxylic acid, it would be easy to remove neutral impurities that might be present from unreacted starting materials or products of incomplete hydrolysis. (That would be what I would try after I knew I was making the cyanohydrin in good yield and was tiring of its isolation and further hydrolysis, but probably not right out of the gate. That's just me.)