RU_KLO
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Simple way to differentiate MEK and THF
Hi, I extracted from PVC glue - used to glue PVC white pipes - a solvent which has Acetone smell.
It was destilated at around 70ºC but my alcohol termometer is not precisely precise (0ºC marks 8ºC and 100º marks 92ºC, so ....)
My first thougt it was MEK, but as now Im trying to get THF, read that its also used for PVC glue.
MEK:79.64 °C
THF: 66 °C
Is there a way to easily diferentiate MEK from THF?
Ideas:
1) just use a more precise termometer and boils some in glass tube (dont know if 14ºC difference is really detectable.)
2) THF should float on water (from wiki: It is lighter than water, with a density of 0.8892 g/cm3 at standard conditions.) MEK should be
dissolved/mixed with water.
Are there simple test for MEK / THF?
Thanks
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Sir_Gawain
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It should say on the can what solvents it contains. I’ve most commonly seen a mixture of MEK and THF. THF is lighter than water, but it is miscible
with it so it won’t separate. A fractional distillation should separate them.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Texium
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THF is miscible with water, so it isn’t going to float on top. MEK actually isn’t fully water soluble, though it still has significant solubility.
They smell significantly different, though if you haven’t smelled either of them in pure form it might be difficult to determine. I always thought
that MEK was like acetone but with somewhat buttery/cheesy undertones. Pretty gross. THF is not as bad. Less cloying, sharper, kinda like a cross
between acetone and diethyl ether.
Chemically, you can test if it’s a ketone by formation of an imine or hydrazone. Dinitrophenylhydrazine is the classic test for ketones and
aldehydes, but other amines or hydrazines would also condense with it to give you a known product you could get a melting point of.
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bnull
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Reaction with sodium bisulfite. Methyl ketones form an adduct with bisulfite that is insoluble in saturated solutions of sodium bisulfite. THF, being
an ether, doesn't react. Make a saturated solution of sodium bisulfite and add a couple of milliliters of the solvent. If a white precipitate appears,
it's MEK; if the solution is still clear, it's THF.
Quod scripsi, scripsi.
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RU_KLO
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Quote: Originally posted by bnull  |
Reaction with sodium bisulfite. Methyl ketones form an adduct with bisulfite that is insoluble in saturated solutions of sodium bisulfite. THF, being
an ether, doesn't react. Make a saturated solution of sodium bisulfite and add a couple of milliliters of the solvent. If a white precipitate appears,
it's MEK; if the solution is still clear, it's THF. |
Will try the bisulfite route.
(I read about "Chemically, you can test if it’s a ketone by formation of an imine or hydrazone. Dinitrophenylhydrazine is the classic test for
ketones and aldehydes, but other amines or hydrazines would also condense with it to give you a known product you could get a melting point of." but
there are reagents out of my league.)
As I dont have Sodium Bisulfite,
1) Can I use Sodium sulfite instead? (which I have)
2) Use the sulfite to generate SO2, and make Bisulfite and use right away.
(I read in the wiki how to make bisulfite. Do not have Vacuum capabilities)
If there is excess of NaOH (because not all was converted to bisulfite) will interfere in the test?
Will bisulfate interfere?
Thanks
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bnull
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| Quote: Originally posted by RU_KLO | As I dont have Sodium Bisulfite,
1) Can I use Sodium sulfite instead? (which I have)
2) Use the sulfite to generate SO2, and make Bisulfite and use right away.
(I read in the wiki how to make bisulfite. Do not have Vacuum capabilities)
If there is excess of NaOH (because not all was converted to bisulfite) will interfere in the test? |
Use sodium bicarbonate instead.
I wonder if you could add the solvent to the bicarbonate solution and then bubble SO2 through it. It would reduce--or even prevent--the
formation of bisulfate.
As an aside, there is a Soviet patent (SU145238A1, translation here, original here), that deals with the recovery of MEK from solutions.
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RU_KLO
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Tried the bisulfite method, first by making it.
in a testube added 3 or 4 gr sodium sulfite, added 5 drops of concentrated H2SO4. Its started to foam.
a bended tube was added with cork at the end of the SO2 generator, and the other end in a test tube containing 10 - 15 ml saturated sodium bicarbonate
solution.
I heat the SO2 generator. It starded bubbling and then the bicarbonate solution tube got a lot of bubbles (CO2) like a soda.
It was finished when the SO2 generator did not generate any gas. (aprox 30 seconds) (Also was affraid of suck back. there was not trap and you can see
it trying to get back when flame (heat source) was removed from generator)
I was left with a milky solution (some sulfur passed over) full of tiny bubbles.
It was filtered with cotton, was not cristal clear, but better.
The Ph was basic (like 8-9) so if sodium bisulfite is Acidic, an excess of bicarbonate was left.
Then it was put in 3 test tubes. the second one was added acetone and the third, the test substance.
(Acetone was used as indicator of which type of precipitation was expected, and if the whole procees works)
On adding acetone, a white ring was observed. (1)
On shaking, both went milky white. (2)
After a while, the acetone test remain white and some flocculent precipitation was seen. The test (THF??) separated in two layers (maybe because of
salting out effect)
Next day in the acetone test tube there was white precipitate. the test (THF??) had some precipitate, but could be sulfur. (not as many as acetone
test tube)
So probably this is THF (or at least no MEK) quite impure. Will recheck the boiling point.
[Edited on 13-5-2024 by RU_KLO]
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Sir_Gawain
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If your solution was alkaline there wouldn’t be any bisulfite, just sulfite.
“Alchemy is trying to turn things yellow; chemistry is trying to avoid things turning yellow.” -Tom deP.
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Texium
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My concern with the bisulfite test is that it could give a false positive for any solvent that is appreciably soluble in water, by causing sodium
bisulfite to precipitate out of the saturated solution. Try using isopropanol as a negative control next time you do it. It shouldn’t give a
precipitate.
And if the solution was still basic, as SirGawain noted, that means you probably just had sulfite, in which case the acetone may have just caused the
sulfite to precipitate on its own rather than forming an adduct, while perhaps your mystery solvent actually is MEK, and isn’t soluble enough in
water to cause precipitation and isn’t forming an adduct since you don’t actually have bisulfite.
[Edited on 5-13-2024 by Texium]
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Bedlasky
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Try iodoform reaction. Methyl ketones give positive test. Just mix sample of your solvent with alkaline solution of iodine and heat it on water bath.
If methyl ketone is present, yellow precipitate of iodoform will form.
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bnull
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It wasn't bisulfite. You should have used an excess of SO2.
Some brands of PVC glue use a mixture of acetone and toluene as solvent. Could you please name the brand you used?
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Texium
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| Quote: Originally posted by Bedlasky | | Try iodoform reaction. Methyl ketones give positive test. Just mix sample of your solvent with alkaline solution of iodine and heat it on water bath.
If methyl ketone is present, yellow precipitate of iodoform will form. |
Great idea! I think that would be a
more reliable test than the bisulfite one, even if authentic bisulfite was available.
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RU_KLO
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| Quote: Originally posted by bnull |
It wasn't bisulfite. You should have used an excess of SO2.
Some brands of PVC glue use a mixture of acetone and toluene as solvent. Could you please name the brand you used? |
it is an 2nd category brand (very cheap) "Amanco" also tried to search for msds. Luckily today found one (last week before starting this, no luck...),
but its for another country (costa rica) maybe same composition.
Número químico/CAS Porcentaje OSHA PEL ACGIH TLV/TWA
Tetrahidrofurano (109-99-9) 30-50% 200 ppm 50 ppm
LD50: 1650 mg/kg (oral, rata) LC50: 18,187 ppm /4h (rata)
Presión de vapor, en mm Hg @20 C: 145
MEK (109-99-9) 8-18 % 200 ppm 50 ppm
LD50: 2737 mg/kg (oral, rata) LC50: 4050 ppm /4h (rata)
Presión de vapor, en mm Hg @20 C: 70.9
Ciclohexanona (108-94-1) 25-40% 50 ppm 20 ppm
LD50: 1535 mg/kg (oral, rata) LC50: 8000 ppm/4h (rata)
Presión de vapor, en mm Hg @20 C: 80.
PVC resina (9002-86-20) 10-20 %
so if the same product, it has THF, MEK, and Ciclohexanone.
So if I want the 3 solvents, destilation...(better fractional- but no capabilities...)
So, if this was the composition, it was a tricky test for the bisulfite, because the THF could contain some MEK....
(and Cyclohexanone from what I read, is a ketone too. But higher boiling point - so probably none was there)
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Texium
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You aren’t going to have any luck separating MEK and THF with simple distillation. A fractionating column is absolutely necessary and even then
it’s not going to be perfect.
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bnull
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| Quote: Originally posted by RU_KLO | | it is an 2nd category brand (very cheap) "Amanco" also tried to search for msds. Luckily today found one (last week before starting this, no luck...),
but its for another country (costa rica) maybe same composition. |
Apparently, no. The composition for Brazil, for example, is:
Acetone: 30-45%;
Methyl Ethyl Ketone: 15-25%;
Mixture of solvents (in fact, ethyl acetate and acetone): 20-30%
| Quote: Originally posted by RU_KLO | So if I want the 3 solvents, destilation...(better fractional- but no capabilities...)
So, if this was the composition, it was a tricky test for the bisulfite, because the THF could contain some MEK....
(and Cyclohexanone from what I read, is a ketone too. But higher boiling point - so probably none was there) |
Then it seems the composition of your glue is different. Perhaps it is acetone-MEK-ethyl acetate too.
Is the solvent partially soluble in water?
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RU_KLO
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from another post:
http://www.sciencemadness.org/talk/viewthread.php?tid=68973&...
Relevant quote from the "Purification of Laboratory Chemicals 6th edition entry for MEK :
"
Quote:
Purification as the bisulfite addition compound is achieved by shaking with excess saturated Na2SO3, cooled to 0°C, filtering off the precipitate,
washing with a little ethyl ether and drying in air; this is followed by
decomposition with a slight excess of Na2CO3 solution and steam distillation, the distillate being saturated with K2CO3 so that the ketone can be
separated, dried with K2CO3, filtered, and distilled.
Interesting that they're using sodium sulfite instead of sodium bisulfite, but the addition compound is certainly stable.
"
So can one confirm if Sodium sulfite (which I have - and probably the experiment before was used) can be used by bisulfite abduct procedure?
thanks,
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bnull
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Thank you for the reference. I wonder why I hadn't thought of that before.
In aqueous solutions, bisulfite is in equilibrium with sulfite (see C. P. Kerr, "Aqueous sodium sulfite, bisulfite and sulfate equilibria"):
$$SO_3^{2-}(aq)+H_2O(l) \rightleftarrows HSO_3^-(aq)+OH^-(aq).$$
The addition of MEK causes the precipitation of the bisulfite adduct, which shifts the equilibrium toward the formation of bisulfite. I don't know the
rate of conversion from sulfite to bisulfite. You may be able to guess it by checking the pH at intervals. Quite interesting.
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