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Topic: Wittig reaction, product 4-vinyl benzioc acid, lab report help  (Read 10034 times)

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Offline catherine0004

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Hi, wondering if anyone could help with 2 tricky lab questions;
in the experiment, 4-bromomethylbenzoic acid in acetone is added to triphenylphosphine to produce 4-carboxybenzyl triphenyl phosphonium bromide.  This is then added to a 37% aqueous formaldehyde solution, 2.5g NaOH in water addedd, the filtrate acidified and the crude product recrystalised with ethanol.
The question is a. Explain why it is possible to generate the yield with aqueous NaOH in this example, and b. If an aldehyde other than formaldehyde were to be used, what would the geometry of the double bond in the product be and why? 
Any help would be MUCH appreciated.
Thanks in advance
Catherine

Offline english

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Re: Wittig reaction, product 4-vinyl benzioc acid, lab report help
« Reply #1 on: April 27, 2007, 02:37:59 PM »
Provide what you're thinking first.

Offline catherine0004

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Re: Wittig reaction, product 4-vinyl benzioc acid, lab report help
« Reply #2 on: April 30, 2007, 08:33:20 AM »
I just realised I'd read the question wrong, it's asking about the YLID, not yield, so I think I understand it now as normally in a wittig reaction you'd expect to use a stronger base like NaH instead of NaOH but in this case the carbanion's stabalised through resonance so you don't need quite as strong a base.
Thanks for offering to help but I think (hope) i've got it figured now unless what i've just wrote is totally the wrong idea!

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