Comments on: Grignard Reagents For Addition To Aldehydes and Ketones

By: Madhav Mittal

Madhav Mittal — Wed, 12 Jun 2024 07:36:50 +0000

I have a doubt
As the Grignard reagent is a very strong base, why will it not react with the acidic alpha hydrogen of the carbonyl compound (which has pka value around 20),and as acid base reactions are must faster than nucleophilic addition reactions why would addition occur?

By: James Ashenhurst

James Ashenhurst — Tue, 21 Mar 2023 14:35:14 +0000

In reply to Prof.Red.

Hi – it’s exothermic, and is thermodynamically favored.

Thermodynamic control is when you can choose the product distribution of an equilibrium mixture by changing the temperature. There is no equilibrium between the Grignard product and the starting materials.

By: Prof.Red

Prof.Red — Sat, 18 Mar 2023 06:14:22 +0000

Hello,
I was just thinking that the reaction to make a grignard is exothermic and reacts spontaneously. Furthermore, oxido/ reduction reactions are thermodynamic reactions (Delta G = -nF(delta)E). Hence, can I conclude that the reaction to make a grignard is under thermodynamic control ?
This feels counter intuitive since the formed organometallic compound is much more reactive and much more unstable then the halogenated one.
I hope you will be able to enlighten me in where I am going wrong.
Thanks for all your great work.

By: James Ashenhurst

James Ashenhurst — Thu, 13 Oct 2022 18:31:18 +0000

In reply to AH. Yes - that would work, as would doing lithium-halogen exchange (e.g. with t-BuLi) and quenching with water

By: AH

AH — Thu, 13 Oct 2022 15:51:16 +0000

How would you convert chlorobenzene back into benzene? Could you do it via a Grignard reagent?

By: James

James — Thu, 06 May 2021 12:34:36 +0000

Greetings! First of all Thank you for creating this website!
Aldehydes and Ketones too are acidic, for eg., acetone can act as an acid, so why don’t they give acid-base reaction with Grignard reagent. Is it because it is a weak acid? Are there any priority order like when will acid-base reaction occur and when nucleophillic addition? Thank you for your help!

By: James

James — Tue, 04 May 2021 17:40:05 +0000

Greetings! First of all thank you so so much for creating such a wonderful website!
Can Cyclohexane be used as a solvent for grignard reagent? My textbook said it can’t be, what can be the reason? It doesn’t seem to have any acidic hydrogen either.
Thanks!

By: James Ashenhurst

James Ashenhurst — Sat, 11 Jul 2020 19:12:41 +0000

In reply to SRK. That would be a really bad synthesis design, since it's unwise to have so many functional groups present on the same molecule. But between these, aldehydes are likely the most reactive.

By: SRK

SRK — Fri, 10 Jul 2020 10:20:02 +0000

What if there are all like aldehydes ketones esters acid halide on same compound , which will react first?

By: James Ashenhurst

James Ashenhurst — Tue, 02 Jun 2020 15:27:37 +0000

In reply to aaisha. Usually doesn't work out the way you want it to (i.e. substitution). Electron transfer followed by reduction of alkyl halide and elimination are both common side reactions. Depends on identity of alkyl halide and the substitution pattern. Even with a cuprate (Gilman reagent) getting a substitution reaction to work on a secondary carbon can be very challenging.