Explosive substances
Perchlorates
All perchlorates should be treated as explosive unless otherwise known. Sodium perchlorate is not explosive but is a powerful oxidising agent and may make a significant contribution to the intensity of any fire. Ammonium perchlorate and many organic salts and heavy metal coordination complexes containing perchlorate ion may explode when heated. The localised heat associated with the preparation of Nujol mulls or KBr discs for infrared spectroscopy may be sufficient to cause an explosion.Perchloric Acid
Perchloric acid forms an azeotrope with water containing 72.5% HClO4. Aqueous solutions containing 72% or less perchloric acid are not in themselves explosive, but such solutions are strong oxidising agents at elevated temperatures and react violently with many compounds.
Wood that has been impregnated with perchloric acid may undergo spontaneous combustion. For this reason, perchloric acid must be stored in a stoppered bottle, which in turn must be kept in a large glass beaker or deep Petri dish.
More information is available in Australian/New Zealand Standard 2243.2.
Other explosive compounds
| These compounds are particularly dangerous and extra precautions must be taken if their preparation is required. |
|---|
| o-Nitrobenzoyl and benzyl chlorides (these explode violently upon distillation), |
| diazonium xanthates (solutions used to prepare thiophenols) |
| organic compounds containing pentavalent iodine |
| picric acid (2,4,6-trinitrophenol) |
| picramide (2,4,6-trinitroaniline) and esters of nitric acid (e.g, ethyl nitrate, pentaerythritol tetranitrate) |
| tetrazoles, pentazoles and their derivatives |
| p-toluenesulfonyl azide and other low MW acyl and sulfonyl azides hydrogen azide, hydrazoic acid, and diazomethane |
Peroxidisable compounds
Peroxide formation in laboratory solvents and reagents has been the cause of many accidents over the years. It is important that you can recognise which compounds have the potential to form peroxides.
Organic compounds that can form allylic or benzylic radicals (cyclohexene and tetralin) or radicals stabilised by an adjacent oxygen (most ethers) are potential peroxide formers. Diisopropyl ether is particularly dangerous. Aldehydes can also form peroxides, although they are not normally a problem. In general, pure compounds are more subject to peroxide buildup.
Alkali metals and their amides are converted to peroxides on prolonged exposure to air.| Some compounds that form peroxides storage | ||
|---|---|---|
| Peroxide Hazard on Storage alone | Peroxide Hazard on Concentration (distillation, evaporation, etc) | Hazardous Due to peroxide Initiation of explosive polymerisation |
| Divinylacetylene Diisopropyl ether Vinylidene chloride Potassium metal Sodium amide | Diethyl ether Dioxan Acetal 1,2-Dimethoxyethane Vinyl ethers Dicyclopentadiene Methylacetylene Decahydronapthalene (Decalin) Tetrahydronapthalene (Tetralin) Tetrahydrofuran Cyclohexene Diethylene glycol Dimethyl ether (Diglyme) | Methyl methacrylate Styrene Acrylic acid Acrylonitrile Butadiene Tetrafluoroethylene Vinylacetylene Vinyl acetate Vinyl chloride Vinylpyridine Chloroprene |
Testing and treatment for ethers containing peroxides
The peroxide test reagent is prepared by mixing the following solutions in a ratio of 10:1:1 (AS/NZS 2243.2 - Appendix D)
- ferrous ammonium sulfate (1% w/v solution)
- sulfuric acid (0.5 mol/L)
- ammonium thiocyanate (0.1 mol/L)
A red coloration on mixing approximately equal volumes of ether and reagent indicates the presence of peroxides. If peroxides are present, they can be removed by passing through a chromatography column containing activated alumina. About 80 g of alumina should be sufficient for a Winchester of ether. The ether should be tested before and after passing through the column.