Organic Peroxides - are they all unstable?

[RyanJ]

Hi there

 

Are Organic Peroxides very unstable? If they are then can anyone explain why?

 

I've read more then a few threads on a few forums where these things are described as potentially explosive but I'm wondering if thet applies to them all and if not can you name one?

 

Can anyone explain why these things are so unstable and also do these things have any practical applications or are they just too dangerous?

 

Cheers,

 

Ryan Jones

[woelen]

Not all organic peroxides are extremely unstable. An example of one, which has a commercial application in the manufacture of resins is MEKP (methyl ethyl ketone peroxide).

 

But, still most of the organic peroxide are very unstable and really dangerous. This has to do with the peroxide bond. A single O-O bond is very weak. It is easily broken. The resulting radicals are VERY reactive and in this way an avalanche effect can be created very easily.

 

Not only organic peroxides are notoriously unstable. Just think of plain H2O2. At higher concentrations, this also is quite a dangerous chemical. Even the commercially available 30% grade material already has to be handled with due care! Many chemical reactions with H2O2 must be carried out at low temperatures.

[RyanJ]

Not all organic peroxides are extremely unstable. An example of one' date=' which has a commercial application in the manufacture of resins is MEKP (methyl ethyl ketone peroxide).

 

But, still most of the organic peroxide are very unstable and really dangerous. This has to do with the peroxide bond. A single O-O bond is very weak. It is easily broken. The resulting radicals are VERY reactive and in this way an avalanche effect can be created very easily.

 

Not only organic peroxides are notoriously unstable. Just think of plain H2O2. At higher concentrations, this also is quite a dangerous chemical. Even the commercially available 30% grade material already has to be handled with due care! Many chemical reactions with H2O2 must be carried out at low temperatures.[/quote']

 

Yea I knew that High conc. [ce]H_2O_2[/ce] was dangerous and unstable, thats one of the reasons I brought this up

 

So, its the acutal O-O bond that causes this problem? In that case why is methyl ethyl ketone peroxide more stable?

 

Cheers,

 

Ryan Jones

[woelen]

MEKP also is quite unstable, but less unstable than most other organic peroxides.

 

The question, why compound A is stable, while compound B with similar features is unstable (or less stable) cannot be answered easily. With advanced mathematical models of molecules, based on quantum mechanics, one can predict stability by means of a 'simulation'. But for most compounds we know, it is just a matter of experimenting, because the computations require MASSIVE amounts of CPU resources and certainly are beyond what the home-chemist can do with his PC .

 

Sometimes, by means of reasoning you can make sensible predictions about a compound's stability.

Indications for low stability are:

1) the presence of extremely high or extremely low oxidation states for a certain element (e.g. manganese (VII) compounds, sodium electride).

2) large mismatches in atomic size (e.g. CI4, with small C atom and 4 large I atoms) with multiple large atoms around a small atom

3) the presence of peroxo and superoxo structures in a compound

4) the presence of oxidizing groups in covalent compounds (best known examples of these are nitrate-esters, chlorate-esters, permanganate-esters and perchlorate-esters).

5) the presence of steric hindrance, which causes strain in molecules

[budullewraagh]

sodium electride? what?

 

also, benzoyl peroxide is more unstable because the carbons at each end of the peroxo group are SP^2 hybridized. i'd imagine that the anomeric effect would come into play as well, with the oxygens in the peroxo group contribute electron density to the antibonding orbitals of the C=O bond, thus rendering the molecule even more unstable.

[jdurg]

As has already been mentioned, pretty much ANY peroxide is unstable. H2O2 decomposes violently at high concentrations, sodium/potassium/rubidium/cesium peroxides are all fairly unstable compounds that react pretty violently once they get going. Organic peroxides are particularly unstable, because the products of their decomposition tend to have very strong bonds. (Numerous double bonds and whatnot). If your products have multiple strong bonds, and the reactants have numerous weak bonds, then the overall reaction will be VERY exothermic. Throw in the fact that the x-O-O-x bond is a pretty weak bond, and you can see why organic peroxides aren't considered the most stable compounds on earth.

 

To add to what woelen has already mentioned, another thing to look for are the bonds involved in the products of the decomposition. If a substance breaks down into substances which have fairly strong bonds, then that adds even more to the instability. This is because once a few molecules have decomposed, the energy released by the formation of these 'strong bonds' will be in excess of the activation energy for the decomposition. This leads to a chain reaction and a violent decomposition.

[RyanJ]

Ah, right I think I get it

 

Are these organic peroxides used for anything or are they just too unstable to bne of any use?

 

 

Cheers,

 

Ryan Jones

[YT2095]

MEKP as Woelen stated is used in resin setting, Benzoyl peroxide is often the active ingredient in Acne medication creams too. there are others used industrialy also, but the majority of them aren`t much good for anything.

it was organic peroxides used at the explosives in London Bombings not so long back, and you saw the damage just a small amount of that could do, no wonder it`s often called "Mother of all Satan"!

[RyanJ]

MEKP as Woelen stated is used in resin setting' date=' Benzoyl peroxide is often the active ingredient in Acne medication creams too. there are others used industrialy also, but the majority of them aren`t much good for anything.

it was organic peroxides used at the explosives in London Bombings not so long back, and you saw the damage just a small amount of that could do, no wonder it`s often called "Mother of all Satan"![/quote']

 

Yea nasty stuff and best avoided by the looks of things!

 

Cheers,

 

Ryan Jones