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Picric-A
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shocked.gif posted on 22-10-2010 at 08:29
Distinguishing two compounds


I have just received two bottles of chemicals, both plastic 100ml bottles.

One contains 2-chloroethanol and one GBL.

Both these chemicals are supposed to be colourless however one of the bottles contains a dark red/brown liquid (!!)

Does anybody know a decent method of distinguishing between these two? preferably it should not use a lot of the compound and should be easy to perform.

Thanks
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Nicodem
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[*] posted on 22-10-2010 at 08:33


bp
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Nicodem
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22-10-2010 at 08:33
Picric-A
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[*] posted on 22-10-2010 at 08:42


Quote: Originally posted by Nicodem  
bp

I thought of this however it uses relatively too much reagent and i dont want toxic 2-chloroethanol fumes near my b.p. apparatus.
Any other?
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[*] posted on 22-10-2010 at 08:45


Boiling point determination is a nondestructive analysis and you need no apparatus, just a couple drops of your compound, a test tube and a thermometer. And why would you want to wait for fumes to escape the test tube?
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smaerd
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[*] posted on 23-10-2010 at 18:21


Or you can go back to the olden days and bust out a theile tube, some mineral oil, a capillary and thermometer :). No fancy devices needed, except maybe a magnifying glass, besides capillaries shouldn't have that much of anything inside of them.

Or maybe if you could get a flask to about -50*C the GBL should become solid while the 2-chloroethanol would remain liquid until about -70*C. Assuming there are no to little impurities.

Or if you have an accurate scale and some small volumetric flasks, you could try to do a density determination. The densities are pretty dang similar and if there is contaminants it would be inaccurate but it's another idea.
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[*] posted on 23-10-2010 at 18:45


Acidified potassium dichromate would make the 2-chloroethanol into 2-chloroethanal, which could be proven to exist with a silver mirror test.

The GBL would just sit there and mock you if you threw some K2Cr2O7/H+ at it.




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Picric-A
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[*] posted on 24-10-2010 at 05:03


I do not have a thermometer high enough to measure the b.p's of both these compounds so i was ideally looking for a chemical test.

Quote: Originally posted by psychokinetic  
Acidified potassium dichromate would make the 2-chloroethanol into 2-chloroethanal, which could be proven to exist with a silver mirror test.

The GBL would just sit there and mock you if you threw some K2Cr2O7/H+ at it.


This would work but the lactone gets hydrolysed by acidified dichromate so both give a positive test and ultimately produce an aldehyde.
Any other chemical test i can use to distinguish the two?

Could the colour have something to do with it? One is a colourless liquid, the other is red/brown. Could the 2-chloroethanol degrade to a reddish compound?
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[*] posted on 24-10-2010 at 05:30


Try adding little chunk of sodium into it. Reaction with chloroethanol will be violent (Wurtz synthesis and "neutralization" between alcohol and alkali metal. Reaction with GBL should be slow, if any...
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Picric-A
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[*] posted on 24-10-2010 at 06:49


Thanks for all the replies so far.

Results from the lab show this;
With sodium the dark red liquid reacted quite violently (indicating it to be 2-chloroethanol) and the colourless liquid barely reacted (indicated lactone) This could be wrong however as the first liquid could contain more water than the other, giving false results.

Reaction with K2Cr2O7/H+; dark red liquid was the first to turn green however the other liquid went green eventually (indicating the dark red liquid was the chloroethanol and the second was the lactone which hydrolysed causing the reduction)

Any more tests which could prove the dark red liquid is the 2-chloroethanol?
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[*] posted on 24-10-2010 at 08:33


Lassaigne sodium fusion test and look for sodium chloride?
You are probably most of the way there if you still have the stuff that was made by adding sodium.
Add water and dilute HNO3 ten test the aqueous extract for Cl- with AgNO3
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[*] posted on 24-10-2010 at 12:07


Quote: Originally posted by Picric-A  


This would work but the lactone gets hydrolysed by acidified dichromate so both give a positive test and ultimately produce an aldehyde.


Oh. Bugger.




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[*] posted on 24-10-2010 at 14:20


Check with silver nitrate and a nucleophile. Ppt of AgCl will occur when the Silver aids departure of the primary chloride. Obviously the nucleophile shouldnt produce a ppt with Ag+ either...

Or the clever way to do it would be to run an IR spec... should be easy to distinguish one from the other.

[Edited on 24-10-2010 by DJF90]
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[*] posted on 24-10-2010 at 14:36


2-chloroethanol reacts with NaOH yielding ethylene oxide (b.p. of 11C.) Perhaps observed bubbling could give you your answer?



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[*] posted on 24-10-2010 at 16:12


Quote: Originally posted by unionised  
Lassaigne sodium fusion test and look for sodium chloride?
You are probably most of the way there if you still have the stuff that was made by adding sodium.
Add water and dilute HNO3 ten test the aqueous extract for Cl- with AgNO3

you could just dry them both beforehand, it should be too hard
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[*] posted on 24-10-2010 at 19:27


I think the pH of GBL would be lower than 2-Chloroethanol. But with impurities maybe not.
Also there's this info from wiki:
"2-Chloroethanol is toxic with an LD50 of 89 mg/kg in rats. Like most organochlorine compounds, chloroethanol combusts to yield hydrogen chloride and phosgene."
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[*] posted on 24-10-2010 at 21:38


Quote: Originally posted by anotheronebitesthedust  
I think the pH of GBL would be lower than 2-Chloroethanol. But with impurities maybe not.
Also there's this info from wiki:
"2-Chloroethanol is toxic with an LD50 of 89 mg/kg in rats. Like most organochlorine compounds, chloroethanol combusts to yield hydrogen chloride and phosgene."


Get yourself a rat.




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[*] posted on 25-10-2010 at 04:43


Quote: Originally posted by madscientist  
2-chloroethanol reacts with NaOH yielding ethylene oxide (b.p. of 11C.) Perhaps observed bubbling could give you your answer?


Hahahaa he doesnt want to be messing with 2-chloroethanol fumes, what makes you think he will play with a toxic, carcinogenic gas?!
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[*] posted on 25-10-2010 at 04:55


It'd be easy enough to just do it outside and stand upwind. But if he doesn't want to uncork that bottle, I do have to wonder why he bought it. :P



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[*] posted on 25-10-2010 at 09:02


Quote: Originally posted by psychokinetic  
Quote: Originally posted by anotheronebitesthedust  
I think the pH of GBL would be lower than 2-Chloroethanol. But with impurities maybe not.
Also there's this info from wiki:
"2-Chloroethanol is toxic with an LD50 of 89 mg/kg in rats. Like most organochlorine compounds, chloroethanol combusts to yield hydrogen chloride and phosgene."


Get yourself a rat.



Haha best answer yet!

To both 1 ml of both liquids was added 4ml conc NaOH. These mixes were boiled for 3 mins then neutralised with HNO3 followed by addition of AgNO3. The dark red liquid gave a white AgCl ppt, the colourless liquid did not.

I think i have more than enough evidence to label the red liquid as 2-chloroethanol and the colourless as the butyrolacone, dont you think? I wonder what caused the red colouration in the first place... i may have to re-distill the 2-chloroethanol before the synthesis... oh dear...
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[*] posted on 26-10-2010 at 00:09


Sounds like it is to me.



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