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Author: Subject: Fractionally distilled benzyl chloride turns blue overnight
Tsjerk
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[*] posted on 8-11-2021 at 08:47


What I meant with dehydration was dehydration of a molecule, so making a new molecule with in total two hydrogen and an oxygen less, which is a known feature when working with sieves. Look at a acetone and sieves.

The above reaction could have been reversed when you added water, which removed the blue color with some time given.

Storing benzyl chloride over sieves shouldn't be a problem as the acid is only produced after hydrolysis, which won't happen without water. Drying the compound with sieves could be a problem as the water will be present in the sieves after drying, but that is not what you did.


[Edited on 8-11-2021 by Tsjerk]
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S.C. Wack
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[*] posted on 8-11-2021 at 14:57


Aldrich says their sieves have a pH of 10.5.

The color of these here is something, probably inorganic, probably bad for the chloride. My sieves certainly don't have this color, and IDK that any sieve intended for drying anything other than air does.

Find one reference of substance where someone dries a benzyl halide with sieves and bad things don't happen...shouldn't be too hard should it, there must be many thousand purifications of them out there.




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[*] posted on 8-11-2021 at 17:16


Quote: Originally posted by S.C. Wack  
The color of these here is something, probably inorganic, probably bad for the chloride. My sieves certainly don't have this color, and IDK that any sieve intended for drying anything other than air does.
I thought the same thing... I got them from here (you will notice that the sieves in the picture aren't the same color/size, lol).
When I got them I was just as suspicious, but I tested them out on alcohols and chlorinated solvents and they seemed to work just fine.
They also don't really have almost any sieve dust. I have some other higher grade 3A sieves that are more typical looking, but they do have some dust. So when I plan on storing something over sieves, I tend to use these ones. I should probably just buy more higher quality sieves, maybe use these ones in the desiccator or something.




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Triflic Acid
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[*] posted on 8-11-2021 at 21:19


Superoxide, I was thinking that it might have been leached out of the cap, the nitrogen-containing dye that is. So maybe try a new bottle?



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[*] posted on 9-11-2021 at 06:46


Quote: Originally posted by Triflic Acid  
Superoxide, I was thinking that it might have been leached out of the cap, the nitrogen-containing dye that is. So maybe try a new bottle?

yeah, that could have been it. It did continue to darken even when moved to a different bottle/cap though.

Also, neither the sample in the test tube or the 20mL sample in the smaller container has turned color. Oh well, I suppose I'll repeat the washing for the entire thing.

Edit: I still have that shitty purple cap, I'll put it on a 100ml bottle with some of the clear BnCl and see what happens.

[Edited on 9-11-2021 by SuperOxide]




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[*] posted on 11-11-2021 at 09:53


So, knowing that it wasn't the cap, it wasn't the sieves, and the color somehow went away after just redoing the workup (water wash, neutralization with sat. Na2CO3, dry with sat NaCl, dry further with anhydrous CaCl2), I figured it was ok to re-process the rest.
At first, I thought I could get by doing it quickly, and I only did a half assed water washing, and 1 Na2CO3 wash, and... it came out just slightly less green, but still green.
I went ahead and actually did a proper workup, and it seems to have worked thus far:


You can kinda tell that it has a slightly yellow color to it, and I'm honestly not sure if that's just because of the light in the picture, because it's much less noticeable in person.

Overall, thus sucks, lol. I lost ~70.2g worth of BnCl, which I worked my ass off to make, just because of some stupid problem that I'm not even sure is actually solved or will go away (the impurity may still be lurking in the BnCl).

But, regardless, I'm calling it quits. If I ever make BnCl again in the future, I will pay more attention to the boiling point of the distilling liquid and the storage container. I know the BP of BnCl is 179°C, but I kept collecting to like ~3 °C past that because the liquid distilling over still looked crystal clear (and I only trust my thermocouple to a few degrees of accuracy). Perhaps something came over that shouldn't have.

Thanks for the input guys. Im not sure I would have tried the water wash right off the bat. I may have jumped to a needless distillation. So that was helpful.




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