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Topic: The famous acid cat dehydration of cyclohexanol to cyclohexene  (Read 5126 times)

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Offline Charkol

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The famous acid cat dehydration of cyclohexanol to cyclohexene
« on: October 27, 2010, 11:17:21 PM »
In this reaction.  Are there any tips to scan through to obtain a maximum and pure return of cyclohexene?

I have found the reaction on wikipedia.  At this point I a curious if there are common mistakes for students in Organic Chem 1 doing this reaction for the first time.  It seems pretty straight forward.  I am familiar with the reactions, somewhat.

I'm not sure what exactly to expect, but say for instance, When I distill the mixture of water H2SO3 and cyclohexanol, will some of the -OSO3H ions come along with the distillate?  The solution will be neutralized by use of sodium carbonate, so this should just take care of all the hydronium ions.  Then it will be washed with water, maybe this will remove the sulfuric anions?  It seemes like water has an affinity to positive ions, so this doesn't seem likely.  My solution after the water wash will be stored with anhydrous calcium chloride.  Maybe these anions will be taken care of at this stage?  The CaCl2 will precipitate out of the solution, taking all of the water molecules with it, hopefully.  So what is the chance that some of the sulfuric anion will still be left in my final product?

Are there any other large ideas to focus on while I prep and execute this lab reaction?

Offline MissPhosgene

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Re: The famous acid cat dehydration of cyclohexanol to cyclohexene
« Reply #1 on: October 27, 2010, 11:21:21 PM »
Ions are water soluble.
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Offline discodermolide

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Re: The famous acid cat dehydration of cyclohexanol to cyclohexene
« Reply #2 on: October 28, 2010, 09:58:43 AM »
Distillable ions, I think not
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Offline Charkol

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Re: The famous acid cat dehydration of cyclohexanol to cyclohexene
« Reply #3 on: October 28, 2010, 10:46:22 AM »
Distillable ions, I think not


This seems true in a theoretical sense, but is this also true in an absolute practical sense as well?

Offline discodermolide

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Re: The famous acid cat dehydration of cyclohexanol to cyclohexene
« Reply #4 on: October 28, 2010, 12:31:59 PM »
Distillable ions, I think not


This seems true in a theoretical sense, but is this also true in an absolute practical sense as well?

Yes
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Offline Charkol

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Re: The famous acid cat dehydration of cyclohexanol to cyclohexene
« Reply #5 on: October 29, 2010, 11:12:15 AM »
Is there a further explanation than this?

I don't seem to understand exactly how. 

If ions are not distillable, then how could the resulting distillate be acidic.  In our experiment of cyclohexanol to cyclohexene, the first distillation produced a distillate that required to be neutralized by use of sodium carbonate. 

Offline discodermolide

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Re: The famous acid cat dehydration of cyclohexanol to cyclohexene
« Reply #6 on: October 29, 2010, 11:27:34 AM »
Is there a further explanation than this?

I don't seem to understand exactly how. 

If ions are not distillable, then how could the resulting distillate be acidic.  In our experiment of cyclohexanol to cyclohexene, the first distillation produced a distillate that required to be neutralized by use of sodium carbonate. 

Perhaps you azeotroped over some of the H2SO4 solution?
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