outer_limits
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Acyl chlorides stability
How stable are acyl chlorides (acetyl, propionyl) in long term storage?
I know that they must be protected from any moisture because they will hydrolise giving carboxylic acid and HCl, but is there any risk of phosgene
formation?
Is it better to convert them to anhydrides for long-term storage?
[Edited on 26-10-2020 by outer_limits]
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clearly_not_atara
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I see no reasonable formation pathway for phosgene from acetyl chloride.
A tiny amount of ketene ought to exist in equilibrium with acetyl chloride but does not accumulate unless there is a base and absolutely no
water present, which is unlikely. Same for propionyl chloride with methylketene. This shouldn't be a risk unless you do something absolutely silly
like storing your acetyl chloride over sodium sulfate (even then I doubt it).
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Cou
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I store several acid chlorides long term. They didn't even require hazmat shipping to buy. For my purpose it doesn't matter if some decomposition to
carboxylic acid happens, because I use them to make esters. Any carboxylic acid contamination could be removed by acid washes of the final product of
whatever reaction you use the acid clhorides for.
But I dunno how important it is to only open the bottles in a glovebox. A tiny amount of conversion of acid chloride to carboxylic acid might happen
every time you open the bottle outside a glovebox, due to a very short exposure to water vapor in the air. I have a bottle of butyraldehyde that
slightly smells of butyric acid due to opening it in air.
Anhydrides also react with water vapor so I don't think it would make a difference.
[Edited on 10-27-2020 by Cou]
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Cou
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*base washes
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FrenchChemist
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If you have purchased chlorides, the original packaging will suffice and the substance will not become anything for years.
If you received it yourself, of course, distillation is the minimum, plus a suitable bottle with a PTFE stopper. Some people flush the bottles with
nitrogen to extend the shelf life, this is an option only for those who have an inert gas on the "occasion" when working with, for example, grignard,
otherwise it is not worth investing in this way of packaging and storage.
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Oxy
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I keep mine in the condition which are far from ideal and they are pretty stable. Original bottle and ziplock do the trick and keep the humidity away.
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woelen
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Quote: Originally posted by Cou  | | But I dunno how important it is to only open the bottles in a glovebox. A tiny amount of conversion of acid chloride to carboxylic acid might happen
every time you open the bottle outside a glovebox, due to a very short exposure to water vapor in the air. I have a bottle of butyraldehyde that
slightly smells of butyric acid due to opening it in air. |
For this reason, I take small working quantities
from my stock bottles and only open the stock bottles if the working quantity is used up. I have 1 liter of acetyl chloride. I put 60 ml in a separate
small bottle and use that for experiments, mostly at test tube scale. Using this strategy, only the 60 ml bottle is opened frequently, the stock
bottle remains good and pure.
I use this strategy for all chemicals, which are moisture sensitive, are easily oxidized, discolor when absorbing air, are very hygroscopic, etc.
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FrenchChemist
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| Quote: Originally posted by woelen | For this reason, I take small working quantities from my stock bottles and only open the stock bottles if the working quantity is used up. I have 1
liter of acetyl chloride. I put 60 ml in a separate small bottle and use that for experiments, mostly at test tube scale. Using this strategy, only
the 60 ml bottle is opened frequently, the stock bottle remains good and pure.
I use this strategy for all chemicals, which are moisture sensitive, are easily oxidized, discolor when absorbing air, are very hygroscopic, etc.
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Good way woelen, or as I asked Mario for a bottle of AcroSeal when I bought products from him, so I can use my chloride with virtually no "contact"
with a needle and syringe and the reagent is still under nitrogen.
Of course, not all substances require such precautions, but I appreciate the quality of the reagent and I prefer some of them to be in good condition
for the longest time
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