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Melgar
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Removing alcohols from nonpolar solvents
I've had to remove alcohols from nonpolar solvents (edit: typically so I can extract some compound, like an amine, amide, or ester that's dissolved in
that nonpolar solvent) more than a few times already, and there doesn't seem to be an easy way to do it. I have quite a bit of sodium and lithium
metal, which will react with the alcohol to form an alkoxide salt. However, these salts also tend to be somewhat soluble in nonpolar solvents.
Perhaps the Williamson ether synthesis would at least give something less polar? That could be an option, except that I often don't want halogenated
alkanes contaminating my nonpolar solvent either.
So, I hit on the idea of reacting the alkoxide salts with chloroacetic acid. I'm not sure if it'd react as an acid or an alkyl halide though. I know
GAA typically doesn't act as an acid unless water is present, and alkoxide salts aren't much more reactive than alkali hydroxides. If the
chloroacetic reaction produces an ether with an acid group, then a concentrated aqueous solution of alkali hydroxide should remove it, along with any
unreacted chloroacetic acid.
Of course, I may be overthinking it, and missing some really obvious solution like CaCl2 or Mg(AcO)2. My instinct is that these would form sludgy
messes that don't separate easily, but I could easily be wrong.
Azeotropic separation works when the alcohol azeotrope (with water) has a lower boiling point than the nonpolar solvent, but this is often not the
case, or there will be something dissolved in the nonpolar solvent that I'm unsure of the boiling point. Plus, the alcohol I use the most, methanol,
doesn't have an azeotrope with water.
The alcohols I typically use are methanol, ethanol, isopropanol, and n-butanol, if that makes a difference. I usually only need to remove small
amounts of alcohols, where there is too little to warrant distillation.
[Edited on 8/20/17 by Melgar]
[Edited on 8/20/17 by Melgar]
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UC235
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If the solvent is compatible with conc. Sulfuric acid, that will strip anything that can be protonated out of them including ethers, alkenes,
alcohols, etc.
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unionised
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Chloroacetic acid will almost certainly act as an acid.
CaCl2 works for the lower MW alcohols.
What solvents are you seeking to remove the alcohols from, and what alcohols?
It may be simpler to cut your losses and buy fresh non-polar solvent.
If you are trying to clean up a saturated hydrocarbon then UC235's suggestions good.
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Magpie
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What is wrong with a water wash for the lower alcohols? Am I missing something?
The single most important condition for a successful synthesis is good mixing - Nicodem
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Melgar
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Let's see.... typically there's something in the nonpolar solvent that precludes me from throwing it away. An amine or amide or ester or something.
Amides and esters might work with H2SO4, but not amines. I suppose I should have mentioned that. My experience so far has been that as long as water
isn't present, amides and esters are fairly resistant to hydrolysis in the presence of alkali metals, at least moreso than alcohols. I could very
well be wrong about that though.
Good to know about CaCl2, although I was never sure if it reacted with any of the compounds I mentioned. It seems to be a bit more acidic that most
chloride salts, although that may just be because of the metathesis reaction with CO2.
edit: yes, I realize that chloroacetic acid would be a very dumb choice for a solvent containing an amine, especially if it isn't at least tertiary.
And I doubt there's a general-purpose method, so I guess I should have specified that I need methods that will preserve each of those functional
groups, especially when heating them tends to produce tar-like polymers.
[Edited on 8/20/17 by Melgar]
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clearly_not_atara
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I think (but not sure) ethanol will react with K2S2O7 forming KHSO4 and KEtSO4, and all three of those salts have very low solubility in any organic
solvents.
EDIT: Actually I'm pretty sure treatment with Na followed by CO2 will convert ROH to NaRCO3 (sodium alkyl carbonate) salts which are insoluble.
[Edited on 20-8-2017 by clearly_not_atara]
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unionised
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CaCl2 will react with amines.
IIRC the "standard" method for hydrolysing amides is to dissolve them in conc H2SO4 then add them to water.
The point is that, even without water, they will dissolve.
It may be easiest to evaporate off all the solvent(s) and then redissolve in clean non-polar solvent.
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Melgar
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I've just confirmed than methanol, but not ethanol, can be salted out of toluene and xylene with KOH flakes. Great news for all the nitrostyrene
reducers out there!
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Magpie
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Try K2CO3.
The single most important condition for a successful synthesis is good mixing - Nicodem
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Corrosive Joeseph
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Quote: Originally posted by UC235  | | If the solvent is compatible with conc. Sulfuric acid, that will strip anything that can be protonated out of them including ethers, alkenes,
alcohols, etc. |
UC235 (or anyone)......... Could you elaborate on that please?
It sounds like a great method of extracting mixed alkanes from
petrol/gasoline.
/CJ
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Corrosive Joeseph
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| Quote: Originally posted by Corrosive Joeseph | | Quote: Originally posted by UC235 | | If the solvent is compatible with conc. Sulfuric acid, that will strip anything that can be protonated out of them including ethers, alkenes,
alcohols, etc. |
UC235 (or anyone)......... Could you elaborate on that please?
It sounds like a great method of extracting mixed alkanes from
petrol/gasoline.
/CJ |
Can I post this again in the hope that some knows more than I do......?
I did also find ths in Vogels 3rd -
"(1) The commercial " n-heptane from petroleum" should be shaken with one
quarter of its volume of concentrated sulphuric acid for several minutes, and the
process repeated until the lower acid layer remains colourless or only very slightly
coloured. If fuming sulphuric acid (containing 10-20 per cent. SO3) is employed,
only 10 per cent, of the volume of the hydrocarbon need be used in each washing :
great care must, of course, be taken in the disposal of the coloured acid layer by
pouring it very slowly into a large excess of water. The hydrocarbon is then washed
twice with water, dried over anhydrous calcium or magnesium sulphate, and distilled.
" n-Hexane from petroleum," b.p. 67-69°, or " petroleum ether, free from
aromatic hydrocarbons," b.p. 60-80°, are also suitable for the above tests. They
must, however, be first purified as described under " n-heptane."
/CJ
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clearly_not_atara
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Sulfuric acid may remove some non-alkane contaminants from gasoline but afaik it will not easily react with aromatic hydrocarbons which are harder to
remove.
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PirateDocBrown
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Concentrated H2SO4 solubility is a standard test, in qualitative organic analysis. It's used to discern alkanes and alkyl halides from alkenes,
alcohols, and carbonyls.
There's no immediate barrier to using it for a purification procedure.
Phlogiston manufacturer/supplier.
For all your phlogiston needs.
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byko3y
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CaCl2 is is most underrated solid extracting agent. Like really, books usually don't mention its properties. For me it's good to know now the
properies of CaCl2, but I'm sure I miss some other options the same way I missed calcium chloride.
However, different people interpret the "non-polar solvent" differently. If we talk about then it's not a nonpolar solvent at all. For example, dipole moment of ethyl
acetate is 1.78 D vs 1.85 for water. And simple amides are strong polar compounds (famous DMF solvent).
Corrosive Joeseph, if you are looking for a method of extracting aromatic compounds from mixture, then there's a lot of other well
developed methods used in petroleum industry (including letting the industry to handle the problem).
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JJay
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Calcium chloride is often recommended for removing alcohols from alkyl halides and ethers. I think it works with esters too, and it certainly works
for alkanes, alkenes, and aromatics like benzene and toluene.
I think there are some issues using it with nitrogen-containing compounds, but I'm not sure exactly what the issues are offhand.
4A molecular sieves will also remove ethanol and methanol.
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byko3y
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Often recommended? By whom? I read about it only once some time ago and I'm unable to find any mentioning in the most popular manuals (e.g. vogel or
orgsyn). Also I can't find the original book with the advise even using google.
4A molecular sieves also remove a lot of other things: critical diameter of methanol is 4.4 A, while critical diameter of most normal alkanes is 4.9
Å. Small gap - small selectivity (compare to the critical diameter of water, which is 3.2 Å).
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Corrosive Joeseph
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No...... I am looking to obtain a relatively pure mix of linear, branched and cyclic alkanes (up to C7) (if I can) from my local brew RON95
Basically home-brew petroleum ether.....
Okay, the quick and dirty low-down.
I have read all there is to read on this but my next round of distillations and experiments on my quest for the OTC NonPolars will probably end up in
a dedicated thread all of it's own.
Almost ready to go again. Lighter fluids and a very common OTC naphtha degreaser are also on to be examined.
I did quite a few fractional distillations of Premium Euro5 Grade last winter.
(Winter blend has a higher content of volatile alkanes than Summer blend for a whole host of reasons I won't go into)
System was sealed, pulling a slight vacuum and reciever was immersed in a large bowl of ice. Condensor was fed it's own supply of ice-water.
My heating source was a boiling water bath but the still-head temperature never exceeded 60dgreesC.
I got many observable fractions, most notably at 35-40c, a huge glut of MBTE at 45c and a fairly steady run of 1-2 drops a second for most of the heat
range, even as soon as I began to apply vacuum.
Can't find all my notes now but I'm fairly certain I was getting about 350ml of crude solvent for every litre of go-go juice (It's cheap - do the
math)
The system was never opened to separate these (Distilling Premium 95 in the house is scary), and no matter how long I boiled that flask, the stillhead
never exceeded the stated 60c above.
Column was a 500ml tube packed with stell scrubbers and insulated 3/4 of the way up with pipe-foam and cable-ties.
So....... Now I have a low boiling mix of alkanes, alkenes and an ether.....
This was used as is in a plant extraction, a known variety, previously experimented on with various polar and NP solvents.
After evaporation the oil was noted to be
'strange consistency, maybe 50% impure, very high yield, obvious waxes, a hint of chlorophyll'
Lower straight chain pure alkanes from another source yield (usually), yield a much purer oil of lower weight (obviously), with no waxes or
chloropyll.
This strange oil was further purified using standard methods.
The solvent was not. And that was shelved for a while.
It was UC235's post above made me think about this some more.
Separation of ethers,alcohols and alkenes from alkanes.......
My thermomter is pretty spot-on, ain't no alcohols or aromatics in there.
Well, that's the condensed version (pardon the pun)
/CJ
[EDIT] - Caffiene Deficiency
[Edited on 10-2-2018 by Corrosive Joeseph]
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JJay
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| Quote: Originally posted by byko3y | Often recommended? By whom? I read about it only once some time ago and I'm unable to find any mentioning in the most popular manuals (e.g. vogel or
orgsyn). Also I can't find the original book with the advise even using google.
4A molecular sieves also remove a lot of other things: critical diameter of methanol is 4.4 A, while critical diameter of most normal alkanes is 4.9
Å. Small gap - small selectivity (compare to the critical diameter of water, which is 3.2 Å). |
I think it's common knowledge... this patent for one: https://www.google.com/patents/US4508929
Vogel and Orgsyn are not exactly founts of common knowledge... most of the information on those is slightly more advanced and arcane. I would think a
more general and introductory lab manual would mention it, but I am not extremely familiar with those (a chemistry professor would be).
This page discusses adducts of calcium chloride with alcohols in brief: http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agen...
I think calcium chloride is actually ok with esters, at least with some esters:
https://hobbychemistry.wordpress.com/2015/04/17/synthesis-of...
With methyl iodide: https://www.youtube.com/watch?v=ZB7YSR3CaUE
Sodium and potassium hydroxide have a strong affinity for covalently bonded hydroxyls but are more expensive (Do I have to cite a source?).
[Edited on 10-2-2018 by JJay]
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happyfooddance
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Vogel does have references to the use of CaCl2 in that capacity. For example in the work up for the diethyl ether prep.
I think the main reason this is usually avoided is that the alcohols increase the solubility of the water in the polar layer and vice versa. Washing
with water can be drastically less efficient, depending on exact solvents and proportions.
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byko3y
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Nice catch on the patent. I actually found it too, but skipped for some reason.
CaCl2 most likely forms adducts with ethers and esters (MgCl2 is known to form 1:1 adduct with ethyl acetate https://dx.doi.org/10.1002/zaac.19633210106 ). "Purification of Laboratory Chemicals" also mentiones the removal of alcohols from ethers with
CaCl2, at the same time they recommend to distill the solvent after that https://books.google.com.ua/books?id=PTXyS7Yj6zUC&pg=PA7...
The authors of the page http://www.chem.ucla.edu/~bacher/Specialtopics/Drying%20Agen... don't seem to be understanding clearly the implications.
Chem Player clearly states that his CaCl2 is used for drying the MeI.
Talking about prefessors, I've just looked up some local board for discussions about capturing alcohols with CaCl2, and many people seem to know that
there's some interaction possible but nobody seems to clearly undestand the interaction. In the end they usually come to opinions like "you should
never mix alcohols and calcium chloride".
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happyfooddance
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| Quote: Originally posted by byko3y |
Talking about prefessors, I've just looked up some local board for discussions about capturing alcohols with CaCl2, and many people seem to know that
there's some interaction possible but nobody seems to clearly undestand the interaction. In the end they usually come to opinions like "you should
never mix alcohols and calcium chloride". |
That may be true, if you are drying these alcohols. But the topic of this thread is removing them.
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JJay
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Some drying agents can be filtered out, but almost everything has some trace solubility in most liquids, so you should almost always distill after
using a drying agent. The only drying agent I am aware of that is regularly used without distillation is molecular sieves, and when using them, it is
usually a good idea to filter through a thick pad of cotton or something to eliminate fine particles.
There are numerous resources that describe how to make ethyl acetate that suggest drying it and removing ethanol with calcium chloride, so I'm pretty
skeptical about the claim that calcium chloride is not compatible with esters, but leaving them standing over calcium chloride for an extended period
of time might not be such a great idea.
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Pumukli
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Corrosive Joeseph: once I was told that unsaturated hydrocarbons are a problem source in fuels because at high temperatures they start to polimerize
and it eventually leads to sticky mess build up in the motor.
So I assume there is not too much alkenes are left for you to get rid of.
On the other hand I saw a detailed composition list of a local E95 unleaded "gasoline". That list was impressive, contained 20+ components, most in
the 2-3% range! These components probably form all sorts of azeotropes with each other.
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byko3y
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There are a lot of pairs solvent-drying agent that can be used to dry the solvent without consequent distillation, e.g. benzene+NaOH, ether+MgSO4,
hexane+CaCl2, DMF+Al2O3, ethanol+CaH2, etc. The more solvent differs from water the more agents capable of removing the water without need for
distillation.
| Quote: Originally posted by JJay | | There are numerous resources that describe how to make ethyl acetate that suggest drying it and removing ethanol with calcium chloride
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Well, that's a weak argument - most of those mentioning it haven't actually verified the method. For
example, if we look at this procedure ( http://www.prepchem.com/synthesis-of-ethyl-acetate/ ), which is from Gattermann's book, we can see that calcium chloride is used as a 1:1 solution
in water. In many cases potassium carbonate or sodium sulfate is prescribed.
Here's another copy of gattermann method: https://books.google.com.ua/books?id=cgg7AAAAIAAJ&pg=PA2...
... and another one https://erowid.org/archive/rhodium/chemistry/ethyl.acetate.h...
In your example https://hobbychemistry.wordpress.com/2015/04/17/synthesis-of... the alcohol is supposedly removed by washing with water, once again not by calcium
chloride. Other writers might suggest otehr salts, calcium chloride is suggested only by historical reasons.
Pumukli, I was always wondering what's in the gasoline. Can you share the data?
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JJay
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| Quote: Originally posted by byko3y | There are a lot of pairs solvent-drying agent that can be used to dry the solvent without consequent distillation, e.g. benzene+NaOH, ether+MgSO4,
hexane+CaCl2, DMF+Al2O3, ethanol+CaH2, etc. The more solvent differs from water the more agents capable of removing the water without need for
distillation.
| Quote: Originally posted by JJay | | There are numerous resources that describe how to make ethyl acetate that suggest drying it and removing ethanol with calcium chloride
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Well, that's a weak argument - most of those mentioning it haven't actually verified the method.
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Whatever, dude. There is no shortage of videos of that procedure, but if you want to see them you can Google them yourself. You have no credible
argument whatsoever.
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