Grignard/Carboxylic Acid Reaction

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Charles Darwin

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I'm reacting 3-Oxobutanoic acid with CH3MgBr in ether. Does the carboanion simply attack the ketone and leave the carboxylic acid...?

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i'm quite certain it attacks the carboxylic acid replacing the OH with the methyl to form another ketone. but i can't find or think of any good thermodynamic reasons for this!

anyone?
 
i'm quite certain it attacks the carboxylic acid replacing the OH with the methyl to form another ketone. but i can't find or think of any good thermodynamic reasons for this!

anyone?

If that did happen it would be from the carboanion from the grignard attacking the partial positive charge on the carbonyl C...
 
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030208_040_grignard_ald_ket.jpg



Does that help?
 
I'm a little confused by the original question. What carbanion are we talking about? Are you calling the partially negative C in CH3MgBr a carbanion? If so, that's not technically correct (since it isn't a true carbanion), but also yes it will attack the carbonyl carbon.
 
I'm a little confused by the original question. What carbanion are we talking about? Are you calling the partially negative C in CH3MgBr a carbanion? If so, that's not technically correct (since it isn't a true carbanion), but also yes it will attack the carbonyl carbon.
:rolleyes: Thanks, I meant the partially-negative-not-carbanion-carbon.

Which carbonyl carbon will it attack? I thought grignards wouldn't react fully in the presence of -OH groups...
 
:rolleyes: Thanks, I meant the partially-negative-not-carbanion-carbon.

Which carbonyl carbon will it attack? I thought grignards wouldn't react fully in the presence of -OH groups...

oh damn that's a good point...even if base is added, then O(2-) is not a very good leaving group. So perhaps the ketone reacts!
 
Ok if the solution is deprotonated with base first, THEN the grignard may react with the ketone.

right?
 
then the first equivalent of the grignard will react with the hydrogen to form methane. Anything after that should react with the ketone.

I think only the ketone side will react with the grignard. So you'll end up with two terminal hydroxyl groups. I'm really bad at naming, so i'm not even going to try.

HOOCCCOOH
 
I think only the ketone side will react with the grignard. So you'll end up with two terminal hydroxyl groups. I'm really bad at naming, so i'm not even going to try.

HOOCCCOOH

the gringard is very sensitive to protons. it reacts with them easily. this is why these reactions are usually performed in very dehydrated conditions (usually even flushing the air with nitrogen to remove water vapor).

so i think the carboxylic hydrogen will react with the gringard.

why do you think that only the ketone will react?
 
the gringard is very sensitive to protons. it reacts with them easily. this is why these reactions are usually performed in very dehydrated conditions (usually even flushing the air with nitrogen to remove water vapor).

so i think the carboxylic hydrogen will react with the gringard.

why do you think that only the ketone will react?

Well, I had an explanation in my head but as I typed it out I realized it didn't support my case. So I really don't know.

To me it seems like a carboxylic acid carbonyl carbon would not be as electrophilic as a ketone/aldehyde because the OH and the carbonyl oxygen would both be trying to withdraw electrons. Since the carbonyl is planar, wouldn't the electron withdrawing effects cancel each other out thus resulting in less of a partial positive on the carbonyl carbon (compared to that of a ketone or aldehyde)?

No idea :/
 
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Well, I had an explanation in my head but as I typed it out I realized it didn't support my case. So I really don't know.

To me it seems like a carboxylic acid carbonyl carbon would not be as electrophilic as a ketone/aldehyde because the OH and the carbonyl oxygen would both be trying to withdraw electrons. Since the carbonyl is planar, wouldn't the electron withdrawing effects cancel each other out thus resulting in less of a partial positive on the carbonyl carbon (compared to that of a ketone or aldehyde)?

No idea :/
It's planar, not linear, so the partial positive would not cancel each other out. If anything, two electron-withdrawing groups would increase the positive charge on the carbonyl carbon.
 
It's planar, not linear, so the partial positive would not cancel each other out. If anything, two electron-withdrawing groups would increase the positive charge on the carbonyl carbon.

Hmm. Well I know that acyl chlorides undergo reactions with gringards. I've never seen or been tested on gringards and carboxylic acids though.
 
reaction at the carboxylic acid would be unfavorable because it would break resonance stabilized bonds.

asking someone to be sure.
 
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reaction at the carboxylic acid would be unfavorable because it would break resonance stabilized bonds.

asking someone to be sure.


Yea that's the other thing I was thinking about, but who knows :/
 
"Consider that a C=O bond straight up will have ~41% ionic character, while a C-O will have only 10%. The bonds in our carboxylate are somewhere in-between [due to resonance]."

So we were close, but off.
 
reaction at the carboxylic acid would be unfavorable because it would break resonance stabilized bonds.

asking someone to be sure.

"Consider that a C=O bond straight up will have ~41% ionic character, while a C-O will have only 10%. The bonds in our carboxylate are somewhere in-between [due to resonance]."

So we were close, but off.

I believe these answer your question. if there is something specific you don't understand, please ask.
 
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