nimgoldman
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Stabilizing ether with BHT
I have obtained some BHT (butylated hydroxytoluene) and I plan to stabilize my diethyl ether with it.
I've read the typical concentration of BHT in ether is 1-6 ppm. Now let's calculate how much BHT to add per liter of ether.
At STP conditions, a liter of ether weighs 713.4 g (density 0.7134 g/cm3). Knowing the molar mass of ether (74.12 g/mol) and molar mass of BHT (220.36
g/mol), we can calculate the weight of BHT needed:
713.4 [g ether] / 74.12 [g/mol ether] = 9.6249 [mol ether]
9.6249 [mol ether] * 1E-6 [ppm] * 220.36 [g/mol BHT] = 0.00212 [g BHT]
In other words, at 1 ppm concentration, there is 2.12 mg of BHT per liter of ether.
Is this correct? Really so little BHT will effectively prevent/slow down formation of peroxides?
Even if being generous, at 6 ppm it is still 12.7 mg of BHT.
I will therefore properly dry the ether (with KOH followed by Na), then re-distill (probably over paraffin oil) and finally mix in something like 15
mg of BHT per liter of ether. Finally, I will store this under argon.
I really want my ether to be stored properly as I am leaving for a longer time and need it to be stored safely.
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Sulaiman
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Why not just add excess BHT to your ether now,
and do the distillation(s) when you are up and running again ?
This way there is no effort required for now,
and you will get fresh ether when you need it.
A sealed bottle of ether will not make much peroxide for several years,
how long do you expect to store your ether ?
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nimgoldman
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Yes it is reasonable to distill it when needed.
I just like to have fresh solvent on hand without needing to distill it though. The little BHT won't affect my applications.
I would store it for a 1-2 months at most before used.
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S.C. Wack
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It's less reasonable if it doesn't need doing and is the most dangerous part of using it...especially since shiny copper is known to keep purified
ether close enough to minty fresh indefinitely.
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unionised
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The use of ppm is a bit like percent.
You should specify whether it's v/v, w/w or w/v. (Or mole/ mole- but that's unusual)
In this case, it hardly matters, and I would assume it's milligrams per litre. so the concentration of BHT should be 1 to 6 milligrams per litre.
The important thing is to check the ether for peroxides before distilling it- even if it had BHT in, and was stored in sealed bottles, in the dark
over copper mesh.
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Sulaiman
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OOPS !
I have to withdraw my comment above
"A sealed bottle of ether will not make much peroxide for several years,
how long do you expect to store your ether ? "
I just combined (quantities 'by eye') 10 ml diethyl ether and 1 ml 10% fresh KI solution and a few drops of 36% HCl
and got a lovely light-piss coloured result,
adding starch made it darker.
So, a 1/3-full 100 ml bottle of Onyxmet diethyl ether does create peroxides if left for c3 years 
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unionised
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Did you test it before you bottled it?
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Sulaiman
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D'oh ! ... No, I did not,
but it is in its original brown glass bottle and has been kept away from direct light.
It did not occur to me at the time to test it,
just c6 months into chemistry hobby at that time, a real noob.
So my observation above is inconclusive ... must try harder.
[Edited on 1-10-2018 by Sulaiman]
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Boffis
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I often recycle ether and therefore have to distil it and then store the unstabilized material for a while at least. I don't have any BHT and haven't
seen it offered in the usual places. Is there an alternative? Say catechol or one of the photographic reducers like metol or amidol? I also have
hydroquinol and pyrogallol.
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DavidJR
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Quote: Originally posted by Boffis  | | I often recycle ether and therefore have to distil it and then store the unstabilized material for a while at least. I don't have any BHT and haven't
seen it offered in the usual places. Is there an alternative? Say catechol or one of the photographic reducers like metol or amidol? I also have
hydroquinol and pyrogallol. |
I got my BHT on eBay from a Chinese seller a while ago. It wasn't too expensive.
Of the compounds you've listed, I'd go for hydroquinone, because I have seen various ethers sold stabilized with hydroquinone. I imagine the others
might also be effective, though.
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