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Topic: Reaction with KCN and DMSO  (Read 9005 times)

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Offline missUK11

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Reaction with KCN and DMSO
« on: April 17, 2012, 02:59:55 PM »
In the attachment there is a reaction but i have worked out two products for it and i dont know which one is correct...can someone help me please?
 ( you may need to scroll to the right a bit to see my products properly below)
Many thanks

Offline Doc Oc

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Re: Reaction with KCN and DMSO
« Reply #1 on: April 17, 2012, 03:13:36 PM »
In the absence of more information, I think your decision to put both products is reasonable.  If your professor has made any other claims (ie; hard vs soft nucleophiles) you'll need to take those into account.  Otherwise, I'm not aware of those reaction conditions favoring either carbonyl or conjugate reduction.

Offline discodermolide

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Re: Reaction with KCN and DMSO
« Reply #2 on: April 17, 2012, 03:41:13 PM »
I think the cyanohydrin will be the major product, the other will certainly form as well but to a minor extent. There is a third possibility as well, in that the CN adds in a conjugate manor followed by attack of CN to give the cyanohydrin.
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« Last Edit: April 17, 2012, 03:55:14 PM by discodermolide »
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Offline orgopete

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Re: Reaction with KCN and DMSO
« Reply #3 on: April 17, 2012, 05:46:36 PM »
I think it is going to be a conjugate addition reaction. Here is why. Aromatic aldehydes and ketones are generally less reactive than aliphatic for addition reactions. The methoxy is probably a slight electron withdrawing group, so it will help rather than hinder.

The other part is the conditions, 100°C in DMSO. I am concerned no protic source is listed. I don't think a cyanohydrin will be stable as the potassium alkoxide. The dimethylalkyl group will decrease reactivity at the beta carbon, so I could understand it being reluctant to add. I think that once added, it will be stable. So I am guessing these are conditions to form a thermodynamic product. I think 1,2-addition is more likely to be a kinetic product.
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Offline me-go

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Re: Reaction with KCN and DMSO
« Reply #4 on: April 18, 2012, 06:35:39 AM »
the following nucleophiles have 1,4 addition:

H2O,ROH,NH2R,Rcoo-,CN-,RS-

so the right product is orginal product but it can be considered the left product because of high temprature and hard conditioning as a secondary product trace.

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Offline missUK11

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Re: Reaction with KCN and DMSO
« Reply #5 on: April 18, 2012, 07:40:45 AM »
Thankss soo much everyone, im gonna choose the product on the "right"

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