Catalyst - 22-10-2003 at 23:28
Does anyone know if UV light will degrade or destabilize organic peroxides?
A google search turned up hits about curing polymers, but I couldn't find an answer to my question.
Thank you.
vulture - 23-10-2003 at 05:58
Interesting question. I've been thinking about this too a few times.
IIRC, UV light should decompose the peroxybond, -O-O-, to a normal oxygen bond, -O-. However, if the endproduct is not energetically favourable I fear
the decomposition could be explosive.
Anyone care to shoot down my lousy theory? 
peroxides
mick - 23-10-2003 at 10:01
Sorry about this, its my third posting today, I must becoming sad.
Anyway, I though that if you have got a benzene type ring in your peroxide, that will absorb the UV and pass the energy on to the peroxide bond, which
is easy to break, giving radicals which can react with anything that is around. Thats how the acivator for car filler works, if the sun is shining it
will set a lot quicker (keep some old activator for a few years and the plastic will fall to bits)
vulture - 23-10-2003 at 10:56
How can you possibly have a benzene type of ring in a cyclic peroxide? The bonding simply doesn't allow any delocalized ring system.
chemoleo - 23-10-2003 at 14:48
Vulture, I think what Mick meant is if you have a peroxide like benzoylperoxide, which is basically C6H5-CO-OO-OC-C6H5, absorption of UV light will
cause breakage of the O-O bond and distribution of the free (radical) electron over the ring system, thus making it a stabilised radical. This indeed
is extremely reactive, and will catalyse reactions much faster. Benzoylperoxide is commonly used as a hardener, just like MEKP, I played with it
myself 
So, sunlight (as it has a large UV proportion) does increase the rate of polymerisation massively.
This also means that other peroxides (like AP, HMTD) are likely to absorb UV light, which will result in the splitting of the O-O bond. Hence I
wouldnt advise storing peroxides under conditions of sunexposure.
I remember once having HMTD in a solution of alcohol (well, not really solution, as it is insoluble). Perfectly stable really, and not really
shocksensitve. However, when I experimented with it, it did so with the sun being high (not intentionally!). After not even 20 minutes I noticed that
lots of bubbles had formed, and this in solution, in a non-aqueous solvent! Clearly, the O-O bond was split, and O2 evolved.
Anyway, I think I may check H2O2 under the UV light tomorrow (say at 220 nm), and see whether bubbles evolve, blanked against H2O... will let you know
of the results 
Gasses evolved by HMTD - UV related?
Chemical Peach - 5-11-2003 at 07:24
I too have observed bubbles bein evolved from HMTD when under water/alcohol but mine has not really exposed to any great deal of UV radiation at all.
I was wondering as to what the bubbles were and had a feeling they might be )2, with the peroxide bond present and all. Does anyone know for sure what
this could be? possibly slow decompositon forming O2 that it acelerated by UV radiation, as i noticed them only once i had disturbed the container
after it had been sitting for around 24hours, whereas i got the impression that chemoleo whitnessed this at a greater rate than this.
what did you see?
Polverone - 5-11-2003 at 15:21
Did you see streams of bubbles rising from the HMTD? Did you see bubbles clinging to the inside of your container? Did you see this under water and
under alcohol, one or the other, or under a mixture of the two? What was the source of water? Tapwater has air dissolved in it that comes out over
time. I'm wondering if that was what you saw or if this was a definite chemical decomposition.
I know that when making HMTD with citric acid, leaving the mixture standing for too long seems to result in a lot of bubbles and the disappearance of
the HMTD.
chemoleo - 5-11-2003 at 16:49
Polverone, I noticed the same thing that when you let the HMTD reaction mixture stand for 3+hrs (although its described like that in COPAE), it is
basically a white paste with lots of bubbles that disappear once it is washed in the filter. Possibly H2O2 is able to decompose the citric acid by
itself, producing oxidation products of C.A. H2O and O2 (and CO2?). Maybe I should test this...
Else, nascent HMTD could also be slowly broken down by remaining H2O2 or C.A. Either possibilites could explain why HMTD has lots of bubbles in the
reaction mix, and also explain why you don't have the problem once it is clean and washed (I stored HMTD in 96% alcohol for weeks in a dark place, and never had a single bubble rising..)
Chemical Peach - 9-11-2003 at 06:01
The bubbles were wittnessed when stored under water, which would have been tap, so that may well explain it. The bubbles did seem to rise from the
HMTD that was settled on the bottom of the coniner. They were quite sparse yet could be taken as 'streams' from the HMTD (although i
don't mean to that there was a large amount). I make HMTD with citric acid and the recent time with the bubbles was refridgerated for ~3 hours
with frequent stirring, then sat for around 90 mins to ppt before filtering and washing. It may be from the water, yet the bubbles definately seemed
to be coming from the HMTD.
Maybe the gas was coming out of the tap water, as you say, but whereas most would make it to the surface before i saw them, some remained trapped
amoung the HMTD at the bottom until disturbed.
chemoleo - 9-11-2003 at 06:32
yo, it's probably the tap water then. It contains lots of ions, some of them which may catalyse breakage of the O-O bond... Distilled water
should be really used at all times to ensure 100% reproducability