I do realise this has been covered but i can't find it in enough detail for my level of competence.
Also to test it you have to open it which is what can set it off,am i correct?
Surly the process can't be as simple as adding 3ml to a couple of potassium iodide crystals and waiting to see if a oily yellow layer appears!! or is
it ?
Would it help to freeze/cool down a lot before opening(less friction?)Ozonelabs - 22-9-2009 at 09:46
It's been our experience, that organic peroxides, while not stable by any definition do not pose too much of a threat in terms of screw-thread
openings.
We were handed a 20 year old bottle of Diethyl ether (That had previously been opened) by someone who didn't want to risk opening it again- so, in an
explosion proof container, we opened it- no explosion. We then decided to test the peroxide content (to 3ml AcOH is added a few KI crystals, 3ml of
the ether to be tested is then added in, the degree of I2 production (characterised by the formation of a yellow-y solution) gives a rough idea as to
peroxide presence) there was the formation of a slight yellow colour that darkened upon shaking (Presumably due to atmospheric oxygen?)
By FAR the worst commonly used peroxide forming ether is THF (in our experience).
This is not ment to downplay the danger of peroxides (Benzoyl Peroxide, for example is quite friction sensetive)- just to demonstrate that perhaps the
real dangers have been blown out of proportion. sonogashira - 22-9-2009 at 10:33
Look at page 163 for details on peroxide detection and treatment method.
Best wishes.
Make or buy some starch:KI test papers. Simply dip into ether/THF/etc. Purple/black = peroxides.
Cheers,
O3 panziandi - 22-9-2009 at 14:31
I use 1mL H3PO4 85% diluted to 3mL with dH2O then add a microspatula of KI, then shake to dissolve (make a few of these in vials), add an equal volume
of ether, also add an equal volume of ethyl acetate to one (other non-peroxide solvents are fine as a blank, for THF use additional water in the blank
opposed to solvent usually) then I shake for 1 minute and judge the colour.
Starch can be added to increase the sensitivity. You can also approximate the peroxide concentration by making a colour chart using known peroxide
solutions (I never bothered with this, basically if its yellow its +ve, treat it!).
Another test is the reduced alkaline phenolphthalein test.
By the way, my isopropanol is MUCH more positive for peroxide than my THF!
Peroxide in ether is easily removed by shaking with 25% sodium hydroxide solution, collecting the ether layer, testing it for peroxide, if it is
positive repeat. If its negative wash with water, dry over sodium, distill from sodium (or similar).
You can also destroy peroxides by refluxing over (IIRC, alkaline) potassium permanganate, shaking with FeSO4/H2SO4. Metabisulphite solution, etc. Some
metal alloys will also destroy peroxides in moist ether. THF tests negative for peroxide (if only faintly yellow in the KI test) by simply standing
over sodium metal (quite a fair bit of H2 released the THF was moist).entropy51 - 22-9-2009 at 14:43
Anhydrous SnCl2 will also remove peroxides and the solvent requires no drying afterward.
Starch-KI paper is more sensitive to peroxides if moistened with 30% AcOH before testing the solvent.Ozone - 22-9-2009 at 18:45
[...more sensitive to peroxides ...]
Yep. You can also dip, dry and then moisten. If your stuff is hot to dry KI:starch paper, then your odds of having *enough* to be a problem are
increased.
You can also partition it and titrate the peroxides.
cheers,
O3
[Edited on 23-9-2009 by Ozone]hodges - 23-9-2009 at 13:38
[Really? I've never heard of any dangers of isoproponol becoming unstable with age.
Hodges
Yep. It's in the literature. J Chem Ed is one that I can think of. An explosion was reported while
distilling isopropanol. Others that people don't usually think of are benzaldehyde, benzyl alcohol, and cyclohexanol.
Scary, isn't it?panziandi - 23-9-2009 at 15:32
I had never heard of explosions resulting from peroxides in isopropanol, but it does form peroxides very easily, and never has inhibitor present. Picric-A - 24-9-2009 at 00:39
Probably because the peroxide formed from isopropanol is much less sensitive/powerfull ect?
[Edited on 24-9-2009 by Picric-A]itchyfruit - 24-9-2009 at 08:59
I'm assuming AcOH is diluted GAA if so what strength?
Sorry to be a pain but i don't really want to just guess at it. Ozonelabs - 24-9-2009 at 09:09
AcOH is just organic shorthand for Acetic Acid.
When I see AcOH in lit. I assume its GAA unless otherwise stated. itchyfruit - 24-9-2009 at 10:32
I had never heard of explosions resulting from peroxides in isopropanol, but it does form peroxides very easily, and never has inhibitor present.
I know alcohol lamps say you should never burn isopropanol, but I always assumed that was because it is less volatile than other alcohols and thus
tends to burn with a sooty flame.
If oxidized, wouldn't isopropanol first form acetone and then TATP? Sounds pretty dangerous to me, but I've never heard any cautions about storing
isopropanol.
Hodges itchyfruit - 24-9-2009 at 15:31
Well so far so good.
I think i may have used a little to much potassium iodide as their was still a little bit in the bottom of the tube after shaking for couple of
minutes,anyway after adding the Di iso propyl ether and shaking i left the mixture for about 5 minutes and it turned a very pale yellow i repeated the
test and got the same pale yellow,but no separation or suspension.
So is this stuff ok or do i need to treat it by one of the methods above.
Also is it ok to soak the small amount i tested onto some cotton wool and ignite it to dispose of it? entropy51 - 25-9-2009 at 06:10
Peroxides in Ethyl Acetate?
There is also a report of peroxides in EtOAc. See here:
Itchy, a very pale yellow may just be from the KI itself. Run a blank alongside your test and compare the two colors. I would probably never distill
isopropyl ether without treating it first, certainly not if it gave a positive test.
The main thing about peroxides is never distill to dryness but leave about 10% of the volume in the still. Some people add mineral
oil to the solvent to be distilled so that the peroxides do not become too concentrated as the solvent is distilled off.panziandi - 25-9-2009 at 07:31
I think peroxides in isopropanol are likely due to the formation of isopropyl hydroperoxide which would be stable in isopropanol solution, until it
becomes too concentrated and hot.
Itchy, you can kind of make up your own method for testing for peroxides. For example the following all give a good indication:
1) 1mL of sample to be tested added to 1mL of acetic acid and a few drops of 5% aqueous KI is added (freshly made and decolourised prior to use with a
spec of sodium sulphite), shaking the sample and a blank (using 1mL of water or petroleum instead of the solvent), within a minute the presence of
yellow, orange, brown will indicate peroxide, compare yellow to the blank.
2) Small quantity of KI (perhaps 0.1g) added to 2 vials with 0.5mL water, add 0.5mL 85% H3PO4, and shake to dissolve, add 1mL of sample and shake for
1 minute, colour changes as above.
3) Add 0.5 ml of the sample to a mixture of 1 ml of fresh 10% aqueous KI (decolourised with a spec of sodium sulphite if needed) and 0.5 ml of dilute
HCl (to which has been added a few drops of starch solution just prior to the test). The appearance of a blue or blue-black color within a minute
indicates peroxides. More sensitive than the above, make sure to run a blank also.
I ran a simple example using THF (old bottle) THF (freshly cleaned) iPrOH and a blank but I couldn't find my camera! Ill do it again later when I
found the camera and post you pisture of the colour changes. But Basically if the ether vial has gone more yellow than the blank, treat it before
using it.
grind - 26-9-2009 at 05:10
A very good stabilizer for ethers and the most peroxide-forming substances is diphenylamine. I use it (following a recommendation) now for many years
and it never disappointed me.
In my experience it is superior to BHT. You can use it together with Na metal or KOH without the danger of salt formation - which makes the stabilizer
ineffective - like in the case of BHT.
Concerning isopropyl alcohol I´m extremely interested in the reference which describes an explosion during distillation.
I repeatedly distilled peroxide-containing isopropanol but always leaved a residue of min. 20% of the whole lot. Then I discarded this residue.
More safe should be to run the distillation process under vacuum.
The abovementioned diphenylamine is now in use to test it´s ability to stabilize isopropanol. To a 100 ml flask containing approx. 60 ml of
anhydrous, freshly distilled isopropanol were added some crystals of the amine. Parafilm was used to seal it. In a few weeks I will make a test with
KI/HCl and report the result.
