SM2
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Quick question
I thought the H2SO4 in making fatty acid esters the classical way, was as H2O scavenger, and catalyst. Is this true? Also, I have seen
esterification of more delicate structures where pyridine free base was used. Does pyridine dehydrate like H2SO4? If not, then I assume it's use in
classical fatty acid/lower alcohol synthesis, is more catalytic, and less about trapping the water. But pyridine is a base, so I guess it could
perform base catalyzed esterification.
But strong bases will beak butyl acetate apart into the alcohol, and acid (which would become the salt).
So I'm a bit confused on all of this. Could anyone clarify this for me? Thanks.
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Dr.Bob
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Sulfuric (and HCl) acid is used to make esters from acids and alcohols, bu works best when the ester distills at lower temps than that product. Or
if the product is stable to the acid (eg, methyl esters of amino acid amine salts using HCl and methanol).
Pyridine is mostly used when making esters via acyl chlorides and alcohols, as it forms an acyl pyridinium species that reacts with the alcohol
reasonably well, and also helps neutralize the HCl from the acyl chloride. Pyridine will not help couple an acid to an alcohol as best as I know
without other reagents. It is NOT a strong enough base to saponify normal alkyl esters, compared to sodium hydroxide. (It might cleave a
nitrophenyl or fluorophenyl ester in some cases.) You cannot perform (strong) base catalyzed esterifications in most cases, only
transesterifications, see biodiesel for that example.
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SM2
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Thank you very much for the info., Dr. Bob. Appreciate it.
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Nicodem
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Thread Moved
30-7-2012 at 06:36 |
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