[xshadow]

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

[chenbeier]

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

[rolnor]

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.

[xshadow]

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

[rolnor]

Yes, the COOH will also be deprotonated.

[chenbeier]

As seen in the link I posted before.

[xshadow]

Thankss!!