GreenD
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Esterification scale-up = problems?!
I did NOT expect to have problems with an esterification reaction.
First trial;
1.5g 4-sulfamoyl benzoic acid compound was put in a 50mL RBF, and filled with ~30mL of methanl and about 7 drops of H2SO4.
The reaction was stirred and refluxed. After 1 hour the solution became clear, colorless (previously white/opaque).
Second trial
20g benzoic acid compound put in 500mL RBF, filled with ~275mL methanol, and 5mL H2SO4
3 hours of reflux and the solution still remains white, opaque.
Trouble shoot options:
1) Add more Methanol
2) Add more H2SO4
3) Both
I am looking for an answer coupled with an explanation as to why - I would assume this would have scaled up very fast. Since the solution is not
clearing up at all, I would first think to add more catalyst.
Any DIFFERENT thoughts?
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White Yeti
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Esterification reactions reach an equilibrium, the addition of a catalyst does not change the equilibrium concentrations of reactants and products,
ever.
You should have been smarter. Read up on how to carry out large scale esterifications beforehand, they are not as simple as high school teachers make
them look. Use a Dean-Stark apparatus to remove water or use a drying tube packed with calcium chloride, calcium sulfate monohydrate, or magnesium
sulfate to remove water, to drive the reaction to the right, and ultimately, to completion.
"Ja, Kalzium, das ist alles!" -Otto Loewi
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Sunil Sharma
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I will suggest u to add more sulphuric acid.... because it will not only act as catalyst but it also act as desiccant that help your reaction to go in
forword direction...
i have personal experence of doing estrification reaction at kilo scale....
[Edited on 24-1-2013 by Sunil Sharma]
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Sunil Sharma
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one more thing as your 4-sulfamoyl benzoic acid is having NH2 group some of your sulphuric acid has been consumed to make salt with the NH2
group...... again i am suggesting you to add more sulphuric acid....
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GreenD
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Not sure how a drying tube would work, but I understand the dean stark trap.
Do you know why a scale up would change anything? There isn't much in the way of heat displacement being a problem that I would see. And the
equilibrium obviously wouldn't change...
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Hexavalent
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The dessicant would absorb the vapourised water formed in the reaction, driving the equilibrium to the right due to the loss of one product from one
side.
"Success is going from failure to failure without loss of enthusiasm." Winston Churchill
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kavu
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"4-Sulfamoyl-benzoic acid methyl ester; To a mixture of 5.16 g 4-carboxylbenzenesulfonamide in 150 ml. methanol was added 6.84 ml sulfuric acid. The
mixture was refluxed overnight and cooled to room temperature. The mixture was evaporated to dryness and the residue was triturated with Et2O. The
formed precipitation was filtered off, washed with Et2O and dried to give 5.2 gram (92percent) of a white solid." WO2009/115515 A1, 2009
"Each substituted benzoic acid 1a–n (0.04 mol) was refluxed for 4 h in 50.0 mL (1.23 mol) of anhydrous methanol and 1.0 mL (2.0 mmol) of sulfuric
acid. The solvent was evaporated and the product obtained washed with cold water." Bioorganic and Medicinal Chemistry, 2009 , vol. 17, # 8 p.
3028 - 3036
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GreenD
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So letting the reaction run over night, it went to completion.
For my work up I simply cool the mixture down to 0°C, at which part both product and reactant fall out of solution. I then vacuum filter, and wash
with Aq. Sodium Bicarb (Dissolves the sulfamoyl-benzoic acid).
Nice!
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