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Author Topic: Could you dry a Tertiary alcohol with a Desiccant?  (Read 6624 times)

Offline SorryDnoodle

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Like the subject suggests, can you? Or is distillation required?


 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #1 on: 01/02/2014 02:41:07 »
Certainly. Activated molecular sieves 3 or 4 should do the trick. You could also use any number of other drying agents, like sodium or calcium hydride, but that would require distillation as well. How dry do you need? Anhydrous magnesium sulfate might be fine for you purposes.
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #2 on: 01/02/2014 04:19:08 »
My needs are not of a high quality, simply function, so it should work fine.

thanks for the tips!
 

Offline Bored chemist

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #3 on: 01/02/2014 15:34:42 »
It's an alcohol: it would react with a hydride.
 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #4 on: 01/02/2014 18:52:04 »
Yes the alcohol will be deprotonated by hydrides, but so will water, which is slightly more acidic than t-butanol or t-pentanol. Assuming water is a minor impurity to start with, adding some base and allowing the mixture to equilibrate will make the distillate drier than it would be otherwise, because water and t-butanol form an azeotrope.
« Last Edit: 01/02/2014 18:58:04 by chiralSPO »
 

Offline Bored chemist

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #5 on: 02/02/2014 10:38:41 »
If you plan to distill it and there's not much water then you don't need any drying agent at all.

On the other hand, if you used calcium oxide or a molecular sieve (as examples) you could decant off the dry solvent and, since the drying agent is pretty much insoluble, you would have pure solvent.

I think some of the sieves might be acid enough to promote dehydration of the alcohol and that might be a problem.
 

Offline CliffordK

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #6 on: 02/02/2014 10:50:48 »
How easy is it to distill the heavier alcohols?

Apparently with the lighter alcohols (ethanol/methanol), one must use a refluxing still, and may only get about 98% purity if one is lucky.
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #7 on: 02/02/2014 19:44:56 »
Thanks for all the advice's, I will try get some calcium oxide and if that fails I will try distillation as well. I prefer non-gaseous methods due to a lack of fume hood but I am working on a home made one but it's a bit off from testing.
 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #8 on: 05/02/2014 17:55:47 »
Which alcohol are you trying to dry? If it's just t-butanol, you can try purifying it by crystallization rather than distillation. Pure t-butanol melts at 25C...
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #9 on: 06/02/2014 20:32:59 »
Which alcohol are you trying to dry? If it's just t-butanol, you can try purifying it by crystallization rather than distillation. Pure t-butanol melts at 25C...

tert-Amyl alcohol, 2-Methyl-2-butanol
 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #10 on: 07/02/2014 14:17:12 »
Then yeah, I'd say calcium oxide followed by distillation would do the trick. It's possible that a filtration might be fine to separate the CaO and alcohol, but I don't know what you need the alcohol for, or how sensitive that might be to calcium or basic impurities...
 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #11 on: 07/02/2014 14:24:38 »
How easy is it to distill the heavier alcohols?

Apparently with the lighter alcohols (ethanol/methanol), one must use a refluxing still, and may only get about 98% purity if one is lucky.

t-amyl alcohol (the one in question) boils at about 100 C, so just a simple distillation won't dry it very well (water and t-amyl alcohol form an azeotrope anyway.) Adding desiccant before distillation will help to dry it.

In a lab, I usually distil solvents like this under substantially reduced pressure, so the boiling point is closer to room temperature. Unfortunately, this would be too expensive for anyone not already equipped to do so...
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #12 on: 07/02/2014 15:27:41 »
Then yeah, I'd say calcium oxide followed by distillation would do the trick. It's possible that a filtration might be fine to separate the CaO and alcohol, but I don't know what you need the alcohol for, or how sensitive that might be to calcium or basic impurities...

I will be using it as a catalyst in this reaction
Potassium hydroxide + Magnesium metal under an inert heavy oil at 250 Celsius with a tert alcohol to reduce the KOH into elemental Potassium.
 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #13 on: 07/02/2014 16:45:24 »
Haha, I thought alkali metals might be the ultimate goal. If you are trying to exclude water, you should also make sure your NaOH is dry...

Since the reaction is taking place in mineral oil, it might be easiest just to make a solution of t-amyl alcohol in mineral oil, which can be added instead of the alcohol itself. You would have to play around with it, but I imagine a 50/50 mix would easily force most of the water into a separate phase (if the mixture gets really cloudy you might need to wait overnight for it to separate. you could also add CaO to this mixture for more effective drying...)

Good luck!
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #14 on: 08/02/2014 09:13:21 »
Haha, I thought alkali metals might be the ultimate goal. If you are trying to exclude water, you should also make sure your NaOH is dry...

Since the reaction is taking place in mineral oil, it might be easiest just to make a solution of t-amyl alcohol in mineral oil, which can be added instead of the alcohol itself. You would have to play around with it, but I imagine a 50/50 mix would easily force most of the water into a separate phase (if the mixture gets really cloudy you might need to wait overnight for it to separate. you could also add CaO to this mixture for more effective drying...)

Good luck!
NaOH? (using KOH)
I have played around with having the alcohol in from the start instead of adding it as it goes along but that doesn't seem to work, Usually I am adding about 1-2 ml of alcohol every 10 minutes after 10 minutes of heating at 250 degrees Celsius, but sometimes the reaction starts without the alcohol and sometimes it doesn't, sometimes it takes 10 minutes, sometimes up to an hour.

I am guessing it all depends on the particle size of my reactants, I tried with powdered Mg before, but some of the Mg became suspended in the oil and it made it impossible to see if any K was produced and I am wondering if Mg can become dissolved in molten Potassium aswell, if that is the case powder might be a bad idea. So I am going to try Magnesium chips instead.

But if my KOH contains water, how would I dry it, simply boil I assume, as it's boiling point is well above 1000 C ?

Also a reason why adding Alcohol early is a mistake, KOH is dissolved in alcohol if I am not mistaken, so I am guessing that would kind of ruin everything^^

And thank you for all the help, I have been trying this experiment for some time now without any good results, most of the time there seems to be a large production of Hydrogen gas once it comes around 250 C and then it just stops as fast ( around 1 sec)


Also: If anyone know where I can find a mineral oil with a density above Potassium's density, I would be forever in your debt, been looking for one the last four months...
« Last Edit: 08/02/2014 09:15:30 by SorryDnoodle »
 

Offline Bored chemist

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #15 on: 08/02/2014 15:00:20 »
Decalin has a density that is greater then the density of potassium.
http://en.wikipedia.org/wiki/Decalin
But I don't think it has a high enough boiling point. There may be alkyldecalins that do meet the requirements.
Drying amyl alcohol by distillation should be relatively easy because it forms an azeotrope with water.


As long as the stuff you are starting with has more than about 72% alcohol, distilling it will give the azeotrope first containing about 28% water until all the water has distilled over then pure alcohol will distill.


I'm not sure there's much point trying to strip out the last of the water from the alcohol because the KOH will contain rather a lot of water.
The normal commercial material is about 85% KOH and most of the other 15% is water.
(For example)
http://www.delcraychem.com/potassium-hydroxide.htm




That water will react with the Mg and be converted to Mg(OH)2 and hydrogen.
You need to allow for that when designing the equipment but the water shouldn't stop the reaction working- you will just need a bit more Mg than you would expect.
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #16 on: 09/02/2014 11:04:50 »
hmm, good idea, so far I have just been using the theoretical requirements.

Thanks for everyone's replies, now I got some work and testing ahead to get the best results, thank you!
 

Offline CliffordK

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #17 on: 09/02/2014 11:53:33 »
Won't it dissolve in a generally hydrophobic solvent such as methylene chloride or diethyl ether which then could be easily distilled out of your solution?

I suppose the problem would be choosing a solvent that you would have easy access to that would give you generally good water/alcohol separation, and good distillation separation.  Perhaps mineral oil.

With the right solvent, you might also be able to separate it from "impurities" using column chromotography, then dry or distill.
 

Offline Bored chemist

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #18 on: 09/02/2014 13:06:09 »
Ether dissolves quite a lot of water.
DCM, not so much, but a mixture of DCM and t pentanol will dissolve water quite well.

If you are going to distill it to remove ether or DCM, you might as well not bother.
You can (as I pointed out) distill it to remove the water.

In any event, the KOH will still add a lot of water to the system.
 

Offline SorryDnoodle

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #19 on: 09/02/2014 13:47:53 »
Ether dissolves quite a lot of water.
DCM, not so much, but a mixture of DCM and t pentanol will dissolve water quite well.

If you are going to distill it to remove ether or DCM, you might as well not bother.
You can (as I pointed out) distill it to remove the water.

In any event, the KOH will still add a lot of water to the system.

Any way to dry the KOH any further?
« Last Edit: 09/02/2014 13:55:57 by SorryDnoodle »
 

Offline CliffordK

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #20 on: 11/02/2014 02:56:34 »
You can probably cook the KOH to dry it. 

When I was looking at biodiesel earlier, one would often use a Sodium or Potassium Methoxide mix.
CH3OH (excess) + NaOH ==> CH3OH + CH3-ONa + H2O
One can get around the problem by using sodium methylate.
CH3OH + CH3ONa ==> CH3OH + CH3ONa (anhydrous).

Anyway, if you add NaOH or KOH to an alcohol, it will deprotonate some of the alcohol, and make water.

Perhaps it is not as big of an issue if the KOH/NaOH was used in excess.

Silica Gel (desiccant often used in packaging, and some kinds if kitty litter) would be much less reactive with your alcohol.  Would it absorb some of the alcohol?
 

Offline Bored chemist

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #21 on: 11/02/2014 21:20:29 »
You can produce the anhydrous solution of sodium methoxide (or methylate if you prefer that name) by the reaction of metallic potassium with a suitable alcohol.

There's a hole in my bucket dear Liza, dear Liza.

Not many things do as good a job of removing water as magnesium does.
 

Offline chiralSPO

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #22 on: 11/02/2014 21:46:23 »
I don't think silica gel would be able to steal much water from NaOH or KOH--cooking it or just adding extra Mg is probably the best way to go...
 

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Re: Could you dry a Tertiary alcohol with a Desiccant?
« Reply #22 on: 11/02/2014 21:46:23 »

 

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