Chemical Forums

Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: xshadow on October 01, 2020, 09:29:23 AM

Title: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: xshadow on October 01, 2020, 09:29:23 AM

Hi
Here I have the steps for this reaction:
(https://i.imgur.com/vIMlFpE.jpg)

I have a doubt:

Why  does pyridine  deprotonate tue -CH₂- group instead of -COOH

I've checked and the pka are:
-COOH ≈ 3.75/4.74
-CH2- (between the COOH groups) ≈ 12

The pyridine should deprotonate the fsr more acidic COOH groups ??? ???

Title: Re: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: chenbeier on October 01, 2020, 09:33:15 AM

I am also wondering, normally Malonicesters are used. But its a modification of Knoevenagel reaction. All acidic H+ will be removed by pyridin, see link.

https://illumina-chemie.de/viewtopic.php?t=4791

Title: Re: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: rolnor on October 01, 2020, 10:43:48 AM

I think the last eliminationstep is catalyzed by acid and therefore the weak pyridine as base and the malonic acid rather than malonic ester is used. Even if pyridine is a weak base there will be some of the malonic CH2-groups deprotonated, its a equilibrium.

Title: Re: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: xshadow on October 01, 2020, 05:02:17 PM

Quote from: rolnor on October 01, 2020, 10:43:48 AM

I think the last eliminationstep is catalyzed by acid and therefore the weak pyridine as base and the malonic acid rather than malonic ester is used. Even if pyridine is a weak base there will be some of the malonic CH2-groups deprotonated, its a equilibrium.

The small amount of malonic molecules with the CH2- group deprotonated  also has the COOH group deprotonated?


Or  it can be some molecule with the -COOH not deprotonated but CH2 deprootnated?

Thanks

Title: Re: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: rolnor on October 02, 2020, 04:31:41 AM

Yes, the COOH will also be deprotonated.

Title: Re: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: chenbeier on October 02, 2020, 03:24:06 PM

As seen in the link I posted before.

Title: Re: Malonic acid + pyridine : Verley-Doebner synthesis
Post by: xshadow on October 02, 2020, 05:27:42 PM

Thankss!!
:)