[jayfivelim]

Can someone explain to me why some peroxides are very unstable? i.e. peroxides formed by picric acid?

[Benzenelover]

I believe it has something to do with the oxygen bond being easy to break, and the oxygen vapor being readily available to react with a nearby carbon compound.

[fledarmus]

Peroxides are molecules containing an oxygen-oxygen single bond. Here is a table of bond energies:

http://www.cem.msu.edu/~reusch/OrgPage/bndenrgy.htm

If you look down the table to an O-O bond, you will find that at 35 kcal/mole, it is one of the weakest bonds listed. That means it takes relatively little energy to separate it into two oxygen radicals, each with an unpaired electron. These are highly reactive compounds, and if you look over the rest of the table, you will find that oxygen makes relatively strong bonds with almost any other element. That means you can get a lot of energy released by breaking a peroxide bond and forming a bond to almost anything else. Consequently, peroxides are very unstable.

[408]

The above answers are correct. 

But Picric acid DOES NOT form peroxides.  It forms metal salts which are sensitive. The acid by itself is harmless.

[Benzenelover]

Peroxides are molecules containing an oxygen-oxygen single bond. Here is a table of bond energies:

http://www.cem.msu.edu/~reusch/OrgPage/bndenrgy.htm

If you look down the table to an O-O bond, you will find that at 35 kcal/mole, it is one of the weakest bonds listed. That means it takes relatively little energy to separate it into two oxygen radicals, each with an unpaired electron. These are highly reactive compounds, and if you look over the rest of the table, you will find that oxygen makes relatively strong bonds with almost any other element. That means you can get a lot of energy released by breaking a peroxide bond and forming a bond to almost anything else. Consequently, peroxides are very unstable.

Awesome link. I've been looking for one of these for a while.

[nox]

The above answers are correct. 

But Picric acid DOES NOT form peroxides.  It forms metal salts which are sensitive. The acid by itself is harmless.

Picric acid by itself is still quite sensitive, especially aged samples.

[408]

The above answers are correct.  

But Picric acid DOES NOT form peroxides.  It forms metal salts which are sensitive. The acid by itself is harmless.

Picric acid by itself is still quite sensitive, especially aged samples.

No.  Have you handled it?  The sensitivity of pure, dry picric acid of any age is quite possibly the most exaggerated hazard in chemistry.

[Benzenelover]

The above answers are correct. 

But Picric acid DOES NOT form peroxides.  It forms metal salts which are sensitive. The acid by itself is harmless.

Picric acid by itself is still quite sensitive, especially aged samples.

No.  Have you handled it?  The sensitivity of pure, dry picric acid of any age is quite possibly the most exaggerated hazard in chemistry.

What if the picric acid is of poor, impure quality? I would imagine it's possible that it could react with some of the contaminants to form a sensitive salt.

[nox]

The above answers are correct. 

But Picric acid DOES NOT form peroxides.  It forms metal salts which are sensitive. The acid by itself is harmless.

Picric acid by itself is still quite sensitive, especially aged samples.

No.  Have you handled it?  The sensitivity of pure, dry picric acid of any age is quite possibly the most exaggerated hazard in chemistry.

Jeez relax. No I haven't handled it, maybe it's exaggerated I don't know. I'm basing my judgment on there being multiple reports of evacuation when old stockpiles of picric acid surfaced in various labs.

[fledarmus]

The above answers are correct.  

But Picric acid DOES NOT form peroxides.  It forms metal salts which are sensitive. The acid by itself is harmless.

Picric acid by itself is still quite sensitive, especially aged samples.

No.  Have you handled it?  The sensitivity of pure, dry picric acid of any age is quite possibly the most exaggerated hazard in chemistry.

Unfortunately, "pure, dry picric acid" is rarely the issue. Although it is relatively shock sensitive, it can be handled. Unfortunately it is also volatile and sublimes at room temperature, forming VERY shock sensitive metal picrates on almost any metal surface it contacts. Usually removing the acid isn't what causes the explosions - it's touching the metal cabinet that the acid has been contained in for the last umpty-ump years and is now coated in a very titchy layer of metal picrates.

[408]

Reports of evacuation is due to people getting overly sensitive whenever something explosive is found.  The only sensitivity comes from huge amounts of metal picrate accumulation.  Picrates are poor initiators of secondary explosives, and picric acid is resistant to initiation, so small picrate impurities will not set off picric acid.  Sublimation is usually only a problem industrially on massive scales.  Furthermore, iron picrate exists as an octahydrate when formed under ambient conditions and is not sensitive.  Only if it were dehydrated (requiring a fire) would the sensitive anhydrous salt be formed.  Touching a metal cabinet covered in iron picrate would not set it off. Only certain picrates are anhydrous and as such sensitive, and these are not common contaminants or structural metals.  ie lead, silver.
Some 2kg drop hammer heights for picric acid, picrates, and other explosives.
Mercury Fulminate 2"
Tetryl 8"
TNT 14"
Picric Acid 14"
Copper Picrate 12"
Zinc Picrate 12"
Ferrous Picrate 14"