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Author: Subject: I think hexane can be used as a Dean-Stark solvent alternative to benzene
Cou
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[*] posted on 1-10-2020 at 20:19
I think hexane can be used as a Dean-Stark solvent alternative to benzene


http://www.sciencemadness.org/talk/viewthread.php?tid=154944

https://cpb-us-e1.wpmucdn.com/blogs.uoregon.edu/dist/1/8309/...

2nd link says hexane and water form an azeotrope boiling at 61.6 C and the vapor is 22.1% water.

One drawback is that salicylic acid is not soluble in hexane. For reactions with salicylic acid, you need benzene or toluene as the solvent.

Right now I am attempting a Dean-Stark fischer esterification with nonanoic acid, 1-pentanol (1.5 mol equiv), and hexane. I will update on how it goes



EDIT: I am very happy to say that it's working fine. Hexane and water are quickly forming layers in the dean-stark trap. Hexane is low boiling so it reduces the amount of reactant escaping the flask

[Edited on 10-2-2020 by Cou]




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Boffis
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[*] posted on 2-10-2020 at 07:25


That's interesting, I have often wonder if hexane or cyclohexane could be used as a substitute for benzene in azeotropic esterifications. Good luck Cou!
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[*] posted on 2-10-2020 at 07:42


I was surprised at how fast the reaction finished, even at the low boiling temperature of hexane. All water was finished separating by 30 minutes, but fischer esterification usually takes several hours.



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[*] posted on 2-10-2020 at 07:46


hexane may lead to solubility issue but its low boiling point probably allow the use a second solvent with higher bp and polarity.



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[*] posted on 2-10-2020 at 08:23


n-butanol can also be used. Again it depends on reactant solubility.
It has non-zero solubility in water but works well for removing water with a dean stark trap.
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Boffis
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[*] posted on 2-10-2020 at 08:30


But won't the butanol also form an ester?
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[*] posted on 2-10-2020 at 09:33


I used hexane succesfully when making esters (to remove water completely), there are some threads here in the forum. Also making anhydrous allylalcohol from azeotrope (70%) worked well. Sometimes I used a fraction obtained by distilling medicinal petrolether, so no pure hexane but mixture of isomers.



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Cou
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[*] posted on 2-10-2020 at 10:03


The nice thing about low boiling point of hexane is that it prevents reagents from escaping into the dean-stark trap, which sometimes messes up separation of water.

If that becomes an issue, you can use a 3 neck flask and periodically add the organic layer in the Dean-stark trap back into the flask

[Edited on 10-2-2020 by Cou]




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Corrosive Joeseph
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[*] posted on 2-10-2020 at 10:55


Toluene.....?


/CJ




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[*] posted on 2-10-2020 at 11:01


I recall using isooctane once when measuring the water content of some greasy stuff.
Worked very nicely.
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[*] posted on 2-10-2020 at 11:48


For some reactions, the boiling point of toluene is too high, which can cause reagents to boil over into the dean-stark trap and not be able to return.

If both of your reagents are high boiling point, like salicylic acid and octyl alcohol, then yea toluene would be okay.




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[*] posted on 4-10-2020 at 16:06


Quote: Originally posted by Boffis  
But won't the butanol also form an ester?


Yes it can, good point since this was for a fischer esterification.
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