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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Steenrod on November 13, 2012, 01:36:07 PM

Title: Why does pure HCN not react with aldehydes and ketones?
Post by: Steenrod on November 13, 2012, 01:36:07 PM

Why does pure HCN not react with aldehydes and ketones?


Thanks.

Title: Re: Why does pure HCN not react with aldehydes and ketones?
Post by: discodermolide on November 13, 2012, 01:40:52 PM

Have you any ideas as to this reaction?

Title: Re: Why does pure HCN not react with aldehydes and ketones?
Post by: Steenrod on November 13, 2012, 01:46:17 PM

I regret to say "None";my knowledge is superficial. :(

All I know is that this the cyanoydrin reaction.

Title: Re: Why does pure HCN not react with aldehydes and ketones?
Post by: discodermolide on November 13, 2012, 01:52:38 PM

Well what do you know about cyanohydrin formation?

Title: Re: Why does pure HCN not react with aldehydes and ketones?
Post by: orgopete on November 13, 2012, 06:10:33 PM

I thought they would react. Do I not understand the question, as in literally true? In the formation of a cyanohydrin, one adds HCN.

Title: Re: Why does pure HCN not react with aldehydes and ketones?
Post by: Steenrod on November 14, 2012, 12:27:42 AM

I just realized that most questions I have posted are actually standard stuff.I have not really read this systematically.

I consulted a few books(not my text!) and here is what I got:

The carbon in HCN is nucleophilic and it bonds with the carbonyl carbon.But HCN is a weak acid and so KCN or NaCN is used in order that free cyanide ion is always present in amounts sufficient to increse the rate of reaction.

So, am I right? And books seem to suggest that the reaction does occur but very slowly.So, the question is not totally correct?(LOL,I picked up a warning because of this)

Title: Re: Why does pure HCN not react with aldehydes and ketones?
Post by: discodermolide on November 14, 2012, 12:37:25 AM

It seems that your books would have a reasonable answer. So they are correct and by default so are you.
http://www.chemguide.co.uk/mechanisms/nucadd/hcntt.html (http://www.chemguide.co.uk/mechanisms/nucadd/hcntt.html)