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Topic: phase transfer catalytic reactions  (Read 14085 times)

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qwerty

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phase transfer catalytic reactions
« on: April 04, 2004, 04:16:43 PM »
In a dichlorocarbene addition to cyclohexene using a phase-transfer catalyst, why is it important to vigorously shake the mixture??

Also, which carbene (:CH2 or :CCl2) would be expected to be more reactive and why?

Thanks
« Last Edit: April 04, 2004, 04:17:17 PM by qwerty »

Offline Mitch

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Re:phase transfer catalytic reactions
« Reply #1 on: April 04, 2004, 08:16:34 PM »
:CH2 is more reactive because the chlorines help stabalize the carbene.
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GCT

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Re:phase transfer catalytic reactions
« Reply #2 on: April 05, 2004, 11:55:54 AM »
Quote
In a dichlorocarbene addition to cyclohexene using a phase-transfer catalyst, why is it important to vigorously shake the mixture??

Recall that a phase transfer reaction requires two phases, one is polar and the other nonpolar.  The catalyst Q+ has a both ionic and a non-polar motif.  The Q+ reacts with the nucleophile, N, through a rather weak bond and is transferred to the nonpolar phase in which the Q and N dissociates, leaving raw N to react with the specified reactant within the nonpolar phase.  Thus the point is to stir up the reaction by shaking it.


Quote
Also, which carbene (:CH2 or :CCl2) would be expected to be more reactive and why?

I would imagine that :CH2 would be more reactive, :CCl2 can donate electrons through delocalization (p-d) and thus stabilize the positive charge.


Quote
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qwerty

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Re:phase transfer catalytic reactions
« Reply #3 on: April 05, 2004, 12:57:43 PM »
Thanks, but can you clarify what N and Q are?

GCT

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Re:phase transfer catalytic reactions
« Reply #4 on: April 05, 2004, 04:46:40 PM »
N is the nucleophile and Q is the transfer catalyst.  You might want to review what phase transfer catalysts are all about as I'm a bit rusty on this topic.

polly

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Re:phase transfer catalytic reactions
« Reply #5 on: April 16, 2004, 07:07:51 PM »
Since chlorine is very electronegative, wouldn't the :CCl2 be more reactive??

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Re:phase transfer catalytic reactions
« Reply #6 on: April 16, 2004, 07:27:54 PM »
Eventhough it is electronegative it can still inductively donate some of it's electron density into the vacant orbital of the carbene. I was told this by a carbene chemist that works for Guy Bertrand. Guy's one of the big shots in the field.
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polly

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Re:phase transfer catalytic reactions
« Reply #7 on: April 16, 2004, 09:03:02 PM »
i see...thanks

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