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Destroyer orgo #31

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huk1985

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Hey, guys I have question on #31 on orgo, the problem is what's the major product when you add Excess D2O and DCl (catalytic) to phenylethanoate. The answer has all the alpha hydrogens replaced with deuteriums and I don't really get why. I know there's probably a simple explanation for this, but orgo is my weakest section and I'd appreciate some help.
Thanks!
 

TeamGuo

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Hey, guys I have question on #31 on orgo, the problem is what's the major product when you add Excess D2O and DCl (catalytic) to phenylethanoate. The answer has all the alpha hydrogens replaced with deuteriums and I don't really get why. I know there's probably a simple explanation for this, but orgo is my weakest section and I'd appreciate some help.
Thanks!

This reaction is just doing an H - D exchange. Think of it as Iodoform reaction where you replace all of the methyl ketone alpha protons with I.

So You can assume, since this is a methyl ketone, oh also, it is not a phenylethanoate, that would be an ester, this is called an acetophenone, it only has 1 alpha carbon since you have the phenyl group attached on the other side.

I believe the logical mechanism would be forming an enolate by deprotonating the alpha proton, and than enolate goes and grabs the D from the D-Cl.

As it grabs the D it kicks off the Cl since it's a good leaving group.

You do this process 3 times to get complete exchange, which is very analogous to the Iodoform reaction. Forming Ph-CO-CI3.

Hope that helped.

Oh and you are working with the alpha H's here because there's no leaving groups here, and since D2O is not a strong nucleophile, and plus it's a methyl ketone, it wants to just grab the acidic H instead of attacking the carbony. :)
 
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