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angelhair
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purifying toluene properly
How do you purify toluene without loosing a lot of it?
I tried to clean 8L of commercial toluene (label said 1000ml/L) with 3 X 800ml commercial 98% H2SO4 (almost clear) stirring for about 20 min each
time. It was sitting in an ice bath and the temp never got above 20 deg C.
So why did I loose about 1.2L? Same thing happened with Xylene.
Every thing I read said to keep below 30 deg C. Did I get sulphonation anyway? What's a girl to do?
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Picric-A
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Distill it over CaCl2 to remove water.
I dont know why you used H2SO4 as sulphonation will take place.
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Panache
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| Quote: | Originally posted by Picric-A
Distill it over CaCl2 to remove water.
I dont know why you used H2SO4 as sulphonation will take place. |
vogel uses this method to remove sulphur based antioxidants from commercial toluene, i simply distill it carefully in the instances i use it. Tried
using the treatment you did anglehair ala vogel and was similarly difficult.
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not_important
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Fractionation followed by the Vogel treatment but using 1/4 the amount of H2SO4 he did and only a single wash with it works OK; this still includes
the post-H2SO4 treatments.
At the time Vogel wrote much of the benzene and toluene on the market were from coal or petroleum processing, and contained a fair amount of sulfur
analogues. Much toluene today is built from alkanes and has much lower sulfur concentration. In solvent grade it may contain methylcyclohexane and
the 1 and 2 double bond analogues, washing with cold KMnO4 solution then Na2CO3, water, dry, and fractionate will get you pretty pure toluene.
You scaled Vogel's method up somewhat, 5 or 10 fold. Without real good stirring and slow acid addition, that's likely to give hot spots and more
sulfonation of the toluene. Chill both the toluene and acid before mixing, too.
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gsd
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"Nitration Grade" Toluene available here (in India) for industrial use is very pure for most applications. Typical GC gives purity 99.8+% and
Carl-Fischer gives moisture less than 0.05%. I believe the Toluene sold in small packing by lab chemicals suppliers and marked as "for synthesis" is
directly repacked from bulk without any purification. Nor will you need any further purification unless it is required for HPLC / TLC analysis.
gsd
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Klute
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What kind of grade wa&s yout toluene? Paint strippers etc nearly always contain methanol, so if it was sucha product, the methanol stayed in the
sulfuric acid as methyl sulfuric acid.... Try directly distilling it slwoly (no need of drying) witha column, and see what temps you get. If it's
paint remover, I'm pretty sure you will have a methanol forerun. In that case, a conc. CaCl2 wash follwoed by drying and distillation shoudl be fine.
The traces of thiophene present will not be harmfull unless you are workign with some sensible catalyst.
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angelhair
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It's a good quality commercial grade from a chemical supplier, but it's not lab grade. It may be technical grade or probably less.
What concentration of KMnO7 is used? Will it remove the thiophenes".
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Klute
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Honestly, I don't think it worth going in the hassle of further purifying it then. there isn't much applicatiosn that require very pur toluene, unless
you are working ina research lab, with sensitives catalyst or organo-metallics. Just distill it and you more than OK, IMHO.
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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panziandi
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Indeed I would say just measure out 600mL portions and fractionally distil it ignore the 1st 50mL collect the following 500mL and leave 50mL in the
flask. Bottle this 500mL. Then add the discarded fractions and some more toluene and repeat. This way you will purify the toluene to a suitable degree
whilst also bottling it into handy sized volumes for use later. No point having large 5L or more bottles since if its something you are using
frequently you will inevitably contaminate the larger bottles. If very high purity is required you can further purify smaller volumes to suit your
needs. I don't have my book at hand but I'm almost certain you reflux over a small quantity of powdered potassium permanganate (something like 0.5-1%
w/v?) then decant it, then dry with calcium chloride, then with sodium wire then distil from sodium under nitrogen and bottle and store over drying
agent. But really such purity is not usually required. Toluene tends to be low sulphur anyway, in fact many suppliers even state that the toluene is
low in sulphur. I don't see why you would need very high purity unless you are doing HPLC or something and even then you should buy HPLC grade since
its been filtered and is guaranteed purity and traceable. A simple distillation will purify it enough for use in recrystalizations etc.
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angelhair
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Thanks for that, I do take your point about the amount of sulphur in the toluene of today.
Just out of curiosity, I put the toluene and H2SO4 in the freezer till about -10 deg C and mixed 3 X 25 ml acid per liter whithout distilling first.
There was hardly any loss of toluene at all but by the 3rd, as the temp increased, some increase in H2SO4 volume was noticed.
This was then washed as normal and distilled. A residue remained which became a hard white solid and burned well. I'm guessing some kind of parrafin.
If I was goining to do this again, I would distill first as you guy's advised.
PS. Is toluene dryed by distillation comparable to that which is dried by CaSO4 or 4A molecular sieves?
[Edited on 3-11-2008 by angelhair]
[Edited on 3-11-2008 by angelhair]
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Klute
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If you dismiss the first 1/4 or so, you will have around 10-20 ppm I think, which is more than enough for any conventional application.
If you plan on using organo-metallics or other very water-sensible reagents, 4A MS will give you under 0.01 ppm water, as will things like LiAlH4,
etc.
To be honest, I don't think extensive drying is needed for most reactions. I used distilled toluene for reaction involving formation of Mg(OMe)2, and
hardly no difference than with 3A MS.
When using NaH, the difference was noticeable, but minimal (a little more H2 evolution at the beggining than with 3A MS). I'm sure fractionnated
toluene could be used with NaH without any major problems in most cases if other drying means are not availble, the amount of NaOH formed being
minimal, especially if the NaH is fresh.
Some quantitative results for solvent drying, from ChemKnowHow.com (excellent source):
http://chemknowhow.com/forum/viewtopic.php?p=562#562
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DrP
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To dry toluene, we used to keep an amount of sodiun wire in the flask - takes out all of the water - quite important for certain polymerisations.
\"It\'s a man\'s obligation to stick his boneration in a women\'s separation; this sort of penetration will increase the population of the younger
generation\" - Eric Cartman
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Klute
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Indeed, simple distn or even CaSO4 would not be enough for anionic polymerisations... and you would need to remove the dissolved O2 anyway, so that
requires sodium or LiAlH4 and inert atmospher... But is that what you need the toluene for AngelHair?
\"You can battle with a demon, you can embrace a demon; what the hell can you do with a fucking spiritual computer?\"
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angelhair
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I don't need super dry toluene for anything yet, it was just an academic question to fill in some knowledge gaps and I am glad there is a site like
this where I can do just that.
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Zinc
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Sorry to revive an old thread, but I didnt want to open a new one for such a simple question.
I have some paint stripper that contains mostly toluene and methanol with some other aliphatic hydrocarbons. I have to remove the methanol from it but
I dont have the equipment needed for distilation, wich would be the best method for removing all of the methanol from the mixture. But as methanol is
miscible with water could a series of simple water washes remove most (at least 95 %) of methanol?
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Jor
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I would wash it a few times with water, followed by drying over anhydrous CaCl2. CaCl2 complexes methanol, that's why you don't dry simple alcohols
with CaCl2.
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Vogelzang
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Sherwin-Williams sells gallons of toluene. No questions asked except "is that all?"
http://www.google.com/#hl=en&source=hp&q=sherwin+wil...
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Zinc
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Interesting.
Can the impure CaCl2 made by dissolving carbonate rock in hydrochloric acid be used to complex the methanol?
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Picric-A
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Yep of course
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12AX7
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Mind that you don't get dolomite, which contains magnesium. MgCl2.6H2O is harder to crystallize and much harder to dry out (as I recall, it cannot be
made anhydrous without loss of HCl).
Loads easier to just buy a sack of Damp-Rid or something.
Tim
[Edited on 9-30-2009 by 12AX7]
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Jimmymajesty
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12AX7: Yes you are right! It is dried in HCl gas to make a MgCl2 support for Ziegler Natta type catalysts.
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jamit
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Anything I should know about purifying toluene by distillation?
I intend to boil and wait for the temperature to rise to 110c before collecting the distillate. has anyone distilled hardware store toluene?
Anything I should know?
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jamit
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is store bought toluene contain any water that I should be worry about? And does water and toluene form an azeotrope? Will this affect my
distillation of toluene?
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ItalianChemist
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toluene can be easily purified, first being shacked with some water, to remove impurities solible in water, then being left a few minutes over Na2SO4,
and dried with 24h over 3A or 4A molecular sieves!
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food
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Is it reasonable to expect a useful answer to a question like this that is being put before people from all quarters of the globe, each with their own
stores and brands? Perhaps a general answer. Maybe a better question would be, how to determine the purity or water content in toluene. I'm not
meaning to be sarcastic or facetious. Who knows, the toluene that is available in your local store may be of a very good purity. There are many posts
on here about store bought reagents that begin with an assumption that store bought = needs cleaning; who knows. I think this has the makings of some
decent experimenting. If you do arrive at any conclusions about the quality of your store bought toluene I for one would be interested to hear about
that. Cheers.
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