chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
mechanism-N-benzylacrylamide synthesis
I committed myself to working through selected reaction mechanisms I run acccross in my reading until I feel I can really push e's at a professional
level. I'm looking at a pretty simple synthesis. N-benzylacrylamide from acrylonitrile and benzyl alcohol in the presence of H2SO4 and I'm just not
getting it. I don't see how the amide function gets made. In particular, I don't see how the carbonyl group gets made leaving the terminal double
bond. I assumed the reactions starts with the alcohol hydroxyl group migrating to the positive charge from the acid leaving an elctrophile which
picks up the e's on nitrogen making that secondary amino function but why the amide carbonyl? Is it the acid? Why isn't the double bond hydrolized?
Could someone with chem draw write the curved arrows for me? Thanks,
CRX
|
|
|
Klute
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
Member Is Offline
Mood: No Mood
|
|
This is how I worked it out, although it could not be what's happening: (I haven't got any drawing software on the computer, you'll have to do with my
lousy description  )
In the presence of H+ aq, the benzylalcohol forms a stable benzylic carbocation, which get's attacked by the N's lone pair, forming a quartenary N
(triple bond to acrylic side, single bond to the benzylic part). The positive charge migrates to the Sp2 carbon, as the N get's it's lone pair back.
This forms a trivalent carbocation, which get's attaked by the nuclephilic molecule H2O, which forms an (amino?-)enol after regeneration of a proton.
BY tautomery (forgot the spelling in english), this enol forms a carbonyl fonction, there you go, an secondary amide!
I guess the double bond doesn't get hydrolysed because it is conjugated (thus stabilized) with the nitrile, and then the amide function.
You'll have to make through this unclear description to get what I'm talking about... But remeber that this is my interpretation, some more
knowledgeable members will surely be able to clear up this issue.
Are considering performing this reaction?
|
|
|
Sergei_Eisenstein
Hazard to Others
Posts: 290
Registered: 13-12-2004
Location: Waziristan
Member Is Offline
Mood: training
|
|
This reaction is also known as the Ritter reaction (follow link for reaction mechanism).
damnant quod non intelligunt
|
|
|
Klute
International Hazard
Posts: 1378
Registered: 18-10-2006
Location: France
Member Is Offline
Mood: No Mood
|
|
So does the reaction proceed well with primary or seconday alcohols, and not only tertiary? I guess benzylic alcohols can be used because of the
stability of their corresponding carbocations... This could be interesting to try out one of these days... I see formic acid is used with
diphenylmethanol, aq. acetic acid could also be a possibility..
|
|
|
chemrox
International Hazard
Posts: 2961
Registered: 18-1-2007
Location: UTM
Member Is Offline
Mood: LaGrangian
|
|
I didn't recognize this as a Ritter. Odd, because I was just planning to work my through the Ritter to understand it a little more.
|
|
|
leu
Hazard to Others
Posts: 368
Registered: 13-10-2005
Member Is Offline
Mood: No Mood
|
|
Generally speaking, alkenes give better yields than the corresponding alcohols
Primary aliphatic alcohols don't react, the most common acid used is sulfuric acid but perchloric, phosphoric, polyphosphoric, substituted sulfonic
acids and boron trifluoride have been used in addition to formic acid in the Ritter reaction 
Chemistry is our Covalent Bond
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
