Sciencemadness Discussion Board - peroxides in thf?

peroxides in thf?

soma - 9-10-2011 at 01:55

After reading thru a few threads I've noticed a few mentions of thf peroxide formation being dangerous.

I've had thf (dry or wet) around for years in metal containers or in brown glass with pieces of metal coat hangers dropped in, and have never seen it develop peroxides. (Tested with "quantofix" peroxide test strips).

peach - 9-10-2011 at 04:50

Quote:

Tetrahydrofuran (THF) is stabilized
with approximately 0.025 weight per-
cent of BHT (3,5-di-tert.-butyl-
4-hydroxytoluene) to inhibit the forma-
tion of explosive-prone peroxides in
autoxidation.
Without the stabilizer, peroxide forma-
tion could take place on prolonged
storage or exposure to air or light.

SeZ BASF.

I'm not sure if normal distillation and handling can diminish, or otherwise render inert, the stabiliser.

An interesting detail in the BASF document is in the storage and handling section, where it suggests it is stored under nitrogen and at 30mBar of pressure (about 1000 is 1 atm).

The 30mBar of pressure was the interesting bit. This is the opposite to SPS systems, where it's stored under positive pressure.

I would guess this is to encourage water to exist in the vapour phase when the stuff is stored at room temperature. The BP of water at that pressure is 6C, although the THF will be there also; in the vapour phase. It will condense again as soon as the container is opened but it must help with the peroxide issue if it's not in the liquid whilst being stored.

I have about 5l of THF. Someone else wants 2.5l but I doubt I'll use all 2.5 myself in anything short of a year plus.

It may make more sense for me to sell off a bit of that and buy another bottle rather than mess around putting it back under nitrogen and vacuum.

If anyone in the UK has D.ether or DMF I could swap you some THF. The chemical company sent my last box to some mystery address neither of us could resolve. The ether it contained disappeared into the metaphorical ether, and that was the last bottle they had. £140's worth of solvents, acids and other bits in there. Some guy has randomly received all that and kept it. Luck him hey!

[Edited on 9-10-2011 by peach]

fledarmus - 10-10-2011 at 04:20

I believe that is supposed to be 30 mbar of positive pressure, which would be ~1030 mbar. At only 30mbar of pressure, the THF would rapidly evaporate at room temp.

Distilled, purified THF can form peroxides within three days under the proper conditions (exposure to air, light). Storage in dark containers under nitrogen with antioxidants (such as BHT) make it much safer to handle.

[Edited on 10-10-2011 by fledarmus]

peach - 10-10-2011 at 09:30

Quote:

I believe that is supposed to be 30 mbar of positive pressure

Good point!

thanos thanatos - 3-1-2012 at 16:12

Is there any reason to think that TBHQ would not be a suitable substitute for BHT for stabilizing THF (and other ethers)?

THF distillation safety

hydride_shift - 30-7-2013 at 18:33

I have some old PVC cement lying around that i've extracted THF from in the past, problem is its 3 years past its use-by-date. Via msds its an equal mix of cyclohexanone and THF

with an undisclosed amount of "substances deemed not harmful" ie: sticky green stuff and BHT.

BTW Heres my rig for distilling low bp (<100*c) OTC solvents

Objective risk assessment?

ScienceSquirrel - 31-7-2013 at 03:26

While I do not want to discourage people from taking precautions with THF I think it is possible to get a bit overcautious.
A full bottle of THF that is tightly capped will not have much opportunity to form peroxides as there is very little oxygen in the bottle. If there is a head space of say 20ml, that is 4ml of oxygen or 2 millimoles!