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Author: Subject: Removing acetone from chloroform
SuperOxide
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[*] posted on 14-2-2021 at 11:14
Removing acetone from chloroform


I made some chloroform using the bleach/acetone method, and while I was pretty sure the bleach was in excess to ensure all the acetone was used up, almost all of it distilled over at about 58 °C (whereas pure chloroform distills over at 61.2 °C). Now since this was a K type thermocouple in a glass tube, it may be safe to assume it was 59 °C, but that's still 2 degrees less than expected. Especially since I have distilled chloroform over before and the thermocouple did read 61 °C, as expected.

I know they form an azeotrope, so I was wondering - would it be possible to remove any acetone that may still be present by just adding some bleach to convert it to chloroform? I understand that chloroform will degrade under alkaline conditions, so perhaps that's not the ideal method. If anyone has a better alternative method, that would be appreciated.

Thank you.
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ChemichaelRXN
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[*] posted on 14-2-2021 at 11:37


You can add water to separate the chloroform from the solution of acetone, but chloroform is slightly soluble in water, so you will loose a bit of it. I guess that is what I would do...a solvent extraction/cleaning and distilled from glass.



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monolithic
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[*] posted on 14-2-2021 at 14:06


Purification of Laboratory Chemicals:

Quote:
Chloroform [67-66-3] M 119.4, b 61.2o, d15 1.49845, d10 1.47060, n15 1.44858. It reacts slowly with oxygen, or oxidising agents, when exposed to air and light, giving, mainly, phosgene, Cl2 and HCl. Commercial CHCl3 is usually stabilized with up to 1% EtOH or of dimethylaminoazobenzene. Simplest purifications involve washing with water to remove the EtOH, drying with K2CO3 or CaCl2, refluxing with P2O5, CaCl2, CaSO4 or Na2SO4, and distilling. It must not be dried with sodium. The distilled CHCl3 should be stored in the dark to avoid photochemical formation of phosgene. In an alternative purification, CHCl3 (500mL) was shaken (mechanically) with several small portions of 12% H2SO4 for 1hour, washed thoroughly with water, saturated NaHCO3, washed again with water, and dried over CaCl2 or K2CO3 (100g) for 1hour before filtering and distilling. After further drying for a short time over P2O5, the CHCl3 was redistilled and stored over Drierite in the dark [Reynolds & Evans J Am Chem Soc 60 2559 1938].

EtOH can be removed from CHCl3 by passage through a column of activated alumina, or through a column of silica gel 4-ft long by 1.75-in diameter at a flow rate of 3mL/minute. (The alumina column, which can hold about 8% of its weight of EtOH, is regenerated by air drying and then heating at 600o for 6hours. It is prepurified by washing with CHCl3, then EtOH, leaving in conc H2SO4 for about 8hours, washing with water until the washings are neutral, then air drying, followed by activation at 600o for 6hours. Just before use it is reheated for 2hour at 154o.) [McLaughlin et al. Anal Chem 30 1517 1958.] Carbonyl-containing impurities can be removed from CHCl3 by percolation through a Celite column impregnated with 2,4-dinitrophenylhydrazine (DHNP), phosphoric acid and water. (Prepared by dissolving 0.5g DHNP in 6mL of 85% H3PO4 by grinding together, then mixing with 4mL of distilled water and 10g of Celite.) [Schwartz & Parks Anal Chem 33 1396 1961]. Chloroform can be dried by distillation from powdered type 4A Linde molecular sieves. For use as a solvent in IR spectroscopy, chloroform is washed with water (to remove EtOH), then dried for several hours over anhydrous CaCl2 and fractionally distilled. This treatment removes material absorbing near 1600 cm-1. (Percolation through activated alumina increases this absorbing impurity). [Goodspeed & Millson Chem Ind (London) 1594 1967, Beilstein 1 IV 42.]

Rapid purification: Pass through a column of basic alumina (Grade I, 10g/mL of CHCl3), and either dry by standing over 4A molecular sieves, or alternatively, distil from P2O5 (3% w/v). Store away from light (to avoid formation of phosgene) and use as soon as possible.


Washing with a quarter volume of acidic (5-10% w/w H2SO4) water , followed by brine, followed by stirring over CaCl2 for 10 minutes worked fine, from personal experience.

[Edited on 2-14-2021 by monolithic]
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Fyndium
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[*] posted on 14-2-2021 at 14:24


The solubility of 10g/L is not too great to be of concern for removing acetone traces. Unless acetone proves detrimental for reactions it's intended to be used, simple watering and brining and drying will likely do well. If I prepare reagents for specific uses, I look how much effort is worth putting in different steps, for example if a reaction is not sensitive to water, it is not necessary to do scrupulous processes to make anhydrous reagents, ethanol being a classic example - if you can do with 95%, even mind few % loss of yield, your life just became a hell of a lot easier.
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[*] posted on 14-2-2021 at 15:26


Quote: Originally posted by ChemichaelRXN  
You can add water to separate the chloroform from the solution of acetone, but chloroform is slightly soluble in water, so you will loose a bit of it. I guess that is what I would do...a solvent extraction/cleaning and distilled from glass.

That sounds easy enough. What do you mean "distilled from glass"? (Hope that's not a stupid question).

Quote: Originally posted by monolithic  
Purification of Laboratory Chemicals:

Quote:
[...]


Washing with a quarter volume of acidic (5-10% w/w H2SO4) water , followed by brine, followed by stirring over CaCl2 for 10 minutes worked fine, from personal experience.

Nice. Whats the point of making the water acidic?

Quote: Originally posted by Fyndium  
The solubility of 10g/L is not too great to be of concern for removing acetone traces. Unless acetone proves detrimental for reactions it's intended to be used, simple watering and brining and drying will likely do well. If I prepare reagents for specific uses, I look how much effort is worth putting in different steps, for example if a reaction is not sensitive to water, it is not necessary to do scrupulous processes to make anhydrous reagents, ethanol being a classic example - if you can do with 95%, even mind few % loss of yield, your life just became a hell of a lot easier.

Yeah, I know it's probably just a little bit in there, but it just bugs me. I was going to add it to the chloroform I have in stock (which distilled at the right temp), but I hate adding something I know will contaminate it (silly, I know).
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[*] posted on 14-2-2021 at 15:50


Quote: Originally posted by SuperOxide  
Nice. Whats the point of making the water acidic?


Acid catalyzed aldol condensation of acetone with itself. Apparently the aldol product is water soluble and chloroform insoluble.
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Fyndium
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[*] posted on 15-2-2021 at 00:09


Quote: Originally posted by SuperOxide  
Yeah, I know it's probably just a little bit in there, but it just bugs me. I was going to add it to the chloroform I have in stock (which distilled at the right temp), but I hate adding something I know will contaminate it (silly, I know).


Not so silly at all. I've had multiple containers of similar stuff that I wouldn't want to mix because they were of different purity. Eventually I cut the crap and either concluded an acceptable purity level, or did further refining on them in the boring days.

At the moment, I have acetone that reeks strongly of piperine. I've kept it in it's own bottle, and it is not useable even for rinsing glassware at the moment because it makes them smell like piperine. I wonder how it could have been carried over, as I used a long fractionation column to separate the acetone. It's only worth few € so it is likely I'll just drain it eventually if I don't figure out any good use for it.
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[*] posted on 15-2-2021 at 06:12


Quote: Originally posted by Fyndium  

At the moment, I have acetone that reeks strongly of piperine. I've kept it in it's own bottle, and it is not useable even for rinsing glassware at the moment because it makes them smell like piperine.
Wow.. small world, lol. I have the exact same thing. Not sure I plan on extracting piperine from pepper again (was just a fun experiment), but if I do, I have some acetone that will be perfect for it for the same reason.
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[*] posted on 15-2-2021 at 08:04


You know where that leads... Eventually you've got dozens of bottles that have colorful labels texted on hand what they contain. "Acetone, from piperine extraction", and "isopropanol, for recrystallization of x", etc. Any true long-term chemist has cabins full of mystery bottles.

I still gotta recrystallize my piperine, it's been desiccating with CaCl2 all this time. Unless I actually need the piperine, it'll be unlikely I'm gonna do it again. Or if I actually do, I get myself a decent sized soxhlet, at least.
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[*] posted on 15-2-2021 at 08:11


Quote: Originally posted by Fyndium  
You know where that leads... Eventually you've got dozens of bottles that have colorful labels texted on hand what they contain. "Acetone, from piperine extraction", and "isopropanol, for recrystallization of x", etc. Any true long-term chemist has cabins full of mystery bottles.

Yep, I'm already there, partner. Ironically, I just disposed of large bottle that held my sulfur containing xylenes that I used for the recryst of sulfur. I figured "Next time I need to recryst some sulfur, I can just re-use this same xylenes"... That was almost over 2 years ago, lol.

Quote: Originally posted by Fyndium  
I still gotta recrystallize my piperine, it's been desiccating with CaCl2 all this time. Unless I actually need the piperine, it'll be unlikely I'm gonna do it again. Or if I actually do, I get myself a decent sized soxhlet, at least.

I did my piperine experiment a while ago, and I did a recryst, poured out the acetone into a bottle for later recrysts, and over the next ±6 months, I unintentionally grew some very nice crystals in the acetone. Happy accident.
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[*] posted on 15-2-2021 at 08:59


Crystallization seems to be the most common happy accident with all kinds of solutions. Happened to me, too, a couple of times with very random stuff.

Stocking recrystallization solvents seem to be best suitable for cases where stuff is routinely processed, aka when producing something. For hobby use, most stuff is "good to have, but likely only used once".
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[*] posted on 16-2-2021 at 14:23


sodium metabisulfite will form an addition product with acetone.
The adduct is very soluble in water and insoluble in chloroform.
Most people just rinse a couple of times with water and call it a day.
The ingredients are cheap and using an excess of chlorinating agent is usually the best method to avoid acetone contamination.
Keeping in mind that the ratio of water to chloroform in the original reaction is rather large to begin with if you use 5 - 10% bleach.
Obviously the situation is different if you are using straight calcium hypochlorite.
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