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Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » Mechanism of base catalyzed ester hydrolysis using other types of bases

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CrimpJiggler

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posted on 15-1-2012 at 01:34

Mechanism of base catalyzed ester hydrolysis using other types of bases

I know the mechanism of a base catalyzed hydrolysis of an ester when a hydroxide is the base but how does it work when other bases such as carbonates or methoxides are used? The carbonate ion can't even act as a nucleophile, can it? I'm guessing methoxide makes a decent nucleophile but if methoxide adds to the carbonyl carbon, you'd just end up with another ester wouldn't you?

UnintentionalChaos

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posted on 15-1-2012 at 08:21

Carbonate forms OH- when dissolved in water.

CO3(-2) + H2O <--> HCO3(-1) + OH-
HCO3(-1) + H2O <--> H2CO3 + OH-

The latter equilibrium occurs to a significantly smaller extent.

With methoxide in methanol (or any alkoxide in the appropriate alcohol), you get transesterification, which is what you describe. This process is used to make biodiesel, for example, by converting the glyceryl triesters of fatty acids into the methyl esters using methoxide in methanol.

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Sciencemadness Discussion Board » Fundamentals » Organic Chemistry » Mechanism of base catalyzed ester hydrolysis using other types of bases