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Topic: Malonic acid + pyridine : Verley-Doebner synthesis  (Read 1030 times)

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Offline xshadow

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Malonic acid + pyridine : Verley-Doebner synthesis
« on: October 01, 2020, 09:29:23 AM »
Hi
Here I have the steps for this reaction:


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 ??? ???

Offline chenbeier

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Re: Malonic acid + pyridine : Verley-Doebner synthesis
« Reply #1 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

« Last Edit: October 01, 2020, 09:47:01 AM by chenbeier »

Offline rolnor

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Re: Malonic acid + pyridine : Verley-Doebner synthesis
« Reply #2 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.

Offline xshadow

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Re: Malonic acid + pyridine : Verley-Doebner synthesis
« Reply #3 on: October 01, 2020, 05:02:17 PM »
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

Offline rolnor

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Re: Malonic acid + pyridine : Verley-Doebner synthesis
« Reply #4 on: October 02, 2020, 04:31:41 AM »
Yes, the COOH will also be deprotonated.

Offline chenbeier

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Re: Malonic acid + pyridine : Verley-Doebner synthesis
« Reply #5 on: October 02, 2020, 03:24:06 PM »
As seen in the link I posted before.

Offline xshadow

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Re: Malonic acid + pyridine : Verley-Doebner synthesis
« Reply #6 on: October 02, 2020, 05:27:42 PM »
Thankss!!
:)

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