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Author: Subject: molecular sieve and acids (esterification)
soma
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[*] posted on 3-6-2017 at 02:38
molecular sieve and acids (esterification)


I'm about to run an esterification reaction using n-acetyl cysteine, ethanol, and sulfuric acid (catalyst).

I want to run it with molecular sieve (3A) to take off the water produced by the reaction.

I'm wondering if the sieve will have problems with the sulfuric?
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j_sum1
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[*] posted on 3-6-2017 at 02:46


You might be interested in this preparation posted by nurdrage.
https://www.youtube.com/watch?v=Ah5ds_3s5BI

Quite a clever idea and a good way of increasing yield.
I am yet to try it myself.
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soma
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[*] posted on 4-6-2017 at 01:07


Thanks for that link.

I'm wondering how necessary the sulfuric would be if the water is removed by molecular sieves. I think in the reaction using n-acetylcysteine, higher temps would cause dimerization (it's run under nitrogen at room temp) http://www.sumobrain.com/patents/wipo/Method-preparation-n-a...

Also, I'm trying to find out if there's a 3A molecular sieve that isn't sensitive to strong acids. There are some sieves that are not acid sensitive.

[Edited on 4-6-2017 by soma]

[Edited on 4-6-2017 by soma]
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j_sum1
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[*] posted on 4-6-2017 at 01:29


I recall asking the same question once. The role of the concentrated sulfuric acid is catalytic -- it is not just there to mop up the H2O produced. So it is still needed.

I don't know about non acid-sensitive molecular sieves. My understanding is that zeolites are damaged by strong concentrated mineral acids. But I am definitely not the best person to ask.
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Waffles SS
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[*] posted on 4-6-2017 at 01:35
Effective way for synthesis of Ethyl ester of carboxylic acids


Quote: Originally posted by soma  
I'm about to run an esterification reaction using n-acetyl cysteine, ethanol, and sulfuric acid (catalyst).

I want to run it with molecular sieve (3A) to take off the water produced by the reaction.

I'm wondering if the sieve will have problems with the sulfuric?


There is no need for adding Molecular sieve in the mixture.Use below schema instead.


3.jpg - 36kB

Formed water make azeotrope with EtOH and Molecular sieve will absorb it.This push equilibrium to Ester side.


[Edited on 4-6-2017 by Waffles SS]
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tshirtdr1
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[*] posted on 9-6-2017 at 18:35


If you heat the reaction flask above the boiling point of water, the sieves won't do you much good. Also, they are expensive and just going to muck up your reaction. If you must use sieves, do it as described above. I have done that and it works well. I have done esterifications over dry silica beads and that works well. Again, you have to keep it below the boiling point of water. Of course, if you are using ethanol, then you shouldn't have a problem with that.

[Edited on 10-6-2017 by tshirtdr1]
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[*] posted on 9-6-2017 at 19:31


Are you sure you have to keep it below the bp of water? Sieves are pretty good at holding on to water and it takes considerable heat and time to fully dry them.
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subskune
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[*] posted on 10-6-2017 at 11:41


what about dry mgso4? It doesn't react with the sulfuric and is an excellent drying agent + it doesn't dissolve much in ethanol.
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