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Oxidizers

Oxidizing agents represent a significant hazard in the laboratory due to their capacity to undergo violent reactions when they come into contact with reducing agents, causing ignition in flammable and combustible materials. Oxidizers can also increase the intensity of a small fire, making safe storage a key consideration in the lab. In addition to the risk of fire, oxidizers may release toxic gases either by reacting with other chemicals, or through decomposition caused by heating. Oxidizers on their own can also have corrosive properties.

Oxidizers may be found in both solid and liquid form. Solid oxidizing agents such as metallic chlorates, perchlorates, nitrates, chromates and permanganates may form explosive mixtures with oxidizable dusts and other suspended particles (e.g. flour, coal dust, magnesium powder, zinc dust, carbon powder).

Liquid oxidizers include nitric acid, chromic acid and sulphuric acid. In addition to being oxidizers, these are also corrosive chemicals. One of the most hazardous liquid oxidizers is perchloric acid, and should be avoided if possible. If perchloric acid must be used, workers must be trained in safe handling procedures and a perchloric acid fume hood designed and constructed for this purpose must be used.

Peroxygen Compounds

Although inorganic peroxides can be hazardous, they are generally stable. However, they may generate peroxides in the presence of organic compounds, or can react violently in the presence of water. More hazardous are organic peroxides, which will be discussed in detail below.

Peroxidizable Organic Chemicals

Introduction

Organic peroxides are carbon-based chemicals that contain the characteristic peroxide (-O-O-) bond. Many organic peroxides are shock, heat, or friction sensitive. The inadvertent production or concentration of organic peroxides have been the cause of many well-documented accidents. Safe handling and storage procedures for hazardous chemicals must be followed when dealing with organic peroxides.

Peroxidizable Organic Chemicals

Peroxide formers are compounds that may react with oxygen, even in low concentrations and temperatures often not considered as hazardous. Peroxidation is a hazard affecting primarily liquid peroxide formers, and solids that are finely divided.

The risk of peroxide formation exists when the compound is exposed to oxygen. This occurs when containers are not properly sealed. Peroxidation occurs more rapidly at elevated temperature and pressure. Blanketing peroxide formers with an inert gas reduces the opportunity for oxygen to reach the compound during storage. Become familiar with the known peroxide formers and classes in the tables below.

Follow these precautions for storing and handling peroxide formers:

  1. Label all known and suspected peroxide formers. Date containers upon receipt and after testing for peroxides.
  2. Store peroxide formers blanketed with an inert gas, such as nitrogen or argon.
  3. Store in original containers or in amber-coloured glass bottles with plastic caps. Containers must be well-sealed, away from sources of light.
  4. Dispense quantities as needed. Do not return unused material to stock container.
  5. Store at cool temperatures, however do not refrigerate. Refrigerating or freezing may cause peroxides to precipitate out.
  6. Peroxidizable chemicals must be dated when received. If the material is kept longer than the recommended storage time the material must be tested for peroxides, and the test date and results attached to the container. If the peroxide content exceeds 100 ppm the material must be disposed of or the peroxides neutralized.    
  7. If possible, add an oxidation inhibitor to increase the safe storage life of peroxide forming organic chemicals. Inhibitors are depleted over time and must be replenished periodically.    
  8. Avoid friction, grinding and any form of impact during handling or transport. Do not use glass containers with metal screw caps or glass stoppers.
  9. Never use a metal spatula, use ceramic or plastic instead.
  10. Follow lab procedures for personal protective equipment and hygiene. Avoid ingestion, inhalation or skin contact.
  11. Procedures which result in evaporation of peroxide formers or extensive exposure to air or oxygen are should be avoided. Distillation of any peroxide former should not be attempted unless the material has been tested for the presence of peroxide. Uninhibited Class C chemicals should not be distilled.

Moieties that may form Peroxides

Ethers and Acetals with alpha Hydrogen
Dienes
Alkenes with alyllic Hydrogen
Vinylalkynes with alpha Hydrogen
Fluoro or Chloroalkenes
Alkylalkyenes with alpha Hydrogen
Vinyl halides, esters or ethers
   


Classes of Peroxide Formers

Class A  Class B Class C
Chemicals that form explosive levels of peroxides without concentration Chemicals that form explosive levels of peroxides on concentration Chemicals that may autopolymerize as result of peroxide accumulation
3 months maximum storage 12 months maximum storage Uninhibited chemicals - 24 hours maximum storage

Inhibited chemicals - 12 months maximum storage

Butadienea
Chloroprenea
Divinylacetylene
Isopropyl ether
Tetrafluoroethylenea
Vinylidene chloride

Acetal
Acetaldehyde
Benzyl alcohol
2-Butanol
Cumene
Cyclohexanol
2-Cyclohexen-1-ol
Cyclohexene
Decahydronaphthalene
Diacetylene
Dicyclopentadiene
Diethyl ether
Diethylene glycol dimethyl ether Dioxanes
Ethylene glycol dimethyl ether 4-Heptanol
2-Hexanol
Isopropyl alcohol
Methylacetylene
3-Methyl-1-butanol
Methylcyclopentane
Methyl isobutyl ketone
4-Methyl-2-pentanol
2-Pentanol
4-Penten-1-ol
1-Phenylethanol
2-Phenylethanol
Tetrahydrofuran
Tetrahydronaphthalene
Vinyl ethers
Other secondary alcohols
Acrylic acidb
Acrylonitrileb
Butadienec
Chloroprenec
Chlorotrifluoroethylene
Methyl methacrylateb
Styrene
Tetrafluoroethylenec
Vinyl acetate
Vinylacetylene
Vinylchloride
Vinylpyridine
Vinyladiene chloride

Notes  

a. When stored as a liquid monomer.
b.  Although these chemicals form peroxides, no explosion involving these monomers has been reported.
c.  When stored in liquid form, these chemicals form explosive levels of peroxides without concentration. They may also be stored as a gas in a cylinder. When stored as a gas, these chemicals may auto polymerize as a result of peroxide accumulation.

References:  

Kelly, Richard J. . U.S. Department of Energ, Lawrence Livermore National Laboratory.

American Chemical Society. Safety in Academic Chemistry Laboratories.

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