Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: slidemat on April 06, 2019, 06:35:22 PM
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Hello everyone!
I struggle to find a way to create a diester (carboxyl group ended) from dicarboxylic acid and diol reaction. I know that when the reaction between two is acid-catalyzed the polycondensation occurs with creation of polyester. I would like to stop the reaction with A-B-A product (where A is coming from a dicarboxylic acid and B - from diol).
Could someone help me with that?
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Relatively simply you have a chance to obtain such esters of oxalic acid with 1,2 and 1,3-diols in diluted solutions.
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If the ester is a 6-membered ring you dont need dilute solution.
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Actually I am looking to obtain a linear product with a structure similar to this:
(https://i.imgur.com/LyZilPG.jpg)
For the policarboxylic acid I would use for example a succinic acid.
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You could use a unsaturated acid, make a di-ester and then cleave/oxidase the doublebonds with permanganate or ozone/hydrogenperoxide
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1). If your dicarboxylic acid can form a cyclic anhydride (as in the given example: succinic anhydride), you simply react 1 mole of the diol with 2 moles the cyclic anhydride without catalysis and preferably, without solvent.
2). Otherwise, you prepare the monomethyl ester of your dicarboxylic acid, followed by transesterification with the diol at 2+/1 molar ratio, under basic catalysis.
You search in the literature for the appropriate monoesterification method because this depends on the structure of the dicarboxylic acid, whether aromatic, conjugated or not.
Indicatively, a method for monoesterification of aliphatic dicarboxylic acids is described in the Vogel’s textbook of practical organic chemistry but the obtained yield is rather moderate.
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Wouldn't the proportions of reactants suffice? An excess of acid. Adding the diol slowly, preferably already diluted?
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Enthalpy,
That's my first gut reaction too, but in doing that you virtually always still end up with some amount of di-substitution. If you don't have a good way to separate them (like a huge polarity difference between mono and bis substitution because you added some greasy group) then it is tricky by its very nature.
This is essentially how a condensation polymerization runs. First you make dimer, then trimer, then tetramer, etc. Usually the low degree of polymerization species hugely dominate until you have high conversion, but there is always a distribution of different -mers.
I think cleverer are approaches like rolnor or pgk suggest, which try to prevent undesired substitution with other pathways.
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Monoesters of dicarboxylic acids can also be prepared in relatively high yields, by transesterification of diesters with the corresponding dicarboxylic acid under acid catalysis.
Organic Syntheses, 19, 45, (1939)
Organic Syntheses, Collective Volume 2, 276, (1943)
http://www.orgsyn.org/demo.aspx?prep=CV2P0276