SECTION 2D: Peroxide Forming Compounds and Reactives

• Recommended Work Practices
• Detection of Peroxides
• Removal of Peroxides

Many chemicals form dangerous peroxides on exposure to air and light. Since they are sometimes packaged in an air atmosphere, peroxides can form even though the containers have not been opened. Peroxides may detonate with extreme violence when concentrated by evaporation or distillation, when combined with other compounds, or when disturbed by unusual heat, shock or friction. Formation of peroxides in ethers is accelerated in opened and partially emptied containers. Refrigeration will not prevent peroxide formation and stabilizers will only retard formation.

Peroxide formation may be detected by visual inspection for crystalline solids or viscous liquids, or by using chemical methods or specialized kits for quantitative or qualitative analysis.

Near the end of this section is a list of examples of peroxidizable compounds that should be extended to include primary and secondary alcohols, allylic-benzylic alcohols, ketones, and, possibly, aralkanes with benzylic hydrogens.

Recommended Work Practices (top)

The following recommendations should be followed to control the hazards of peroxides.

• Know the properties and hazards of all chemicals you are using through adequate research and study, including reading the label and MSDS.
• Inventory all chemical storage at least twice a year to detect forgotten items, leaking containers, and those that need to be discarded.
• Identify chemicals that form peroxides or otherwise deteriorate or become more hazardous with age or exposure to air. Label containers with the date first opened and the date for disposal as recommended by the supplier.
• Minimize peroxide formation in ethers by storing in tightly sealed containers placed in a cool place in the absence of light. Do not store ethers at or below the temperature at which the peroxide freezes or the solution precipitates.
• Choose the size container that will ensure use of the entire contents with in a short period of time.
  
• Require testing for peroxides of any opened containers before use.
• Clean up spills immediately (Section 8). The safest method is to absorb the material onto vermiculite or a similar loose absorbent.
  
• When working with peroxidizable compounds, wear impact-resistant safety eyewear and face shields. Visitor specs are intended only for slight and brief exposure, and should not be used when working with peroxidizable compounds.
  
• Do not use solutions of peroxides in volatile solvents under conditions in which the solvent might be vaporized. This could increase the concentration of peroxide in the solution.
  
• Do not use metal spatulas or magnetic stirring bars (which may leach out iron), since contamination with metals can lead to explosive decomposition. Ceramic, Teflon or wooden spatulas and stirring blades are usually safe to use.
  
• Do not use glass containers with screw-top lids or glass stoppers. Polyethylene bottles with screw-top lids may be used.
  

TABLE 2: Examples of Peroxidizable Compounds

* Under storage conditions in the liquid state the peroxide-forming potential increases and certain of these monomers(especially butadiene, chloroprene, and tetrafluoroethylene) should be discarded after three months.

Detection of Peroxides (top)

The following procedures can detect most peroxides. Do not perform these tests on materials (such as metallic potassium) that may be contaminated with peroxides.

• Prepare reagent by adding 100-mg sodium iodide (NaI) or potassium iodide (KI) crystals to 1.0 ml of glacial acetic acid. Add 0.5 to 1.0 ml of material being tested to an equal volume of reagent. A yellow color indicates a low concentration (~0.1 per cent) and brown a high concentration of peroxide in the sample. A blank should be run, using some non-peroxidizable compound such as pure n-hexane.
• Peroxide test strips, which change color to indicate the presence of peroxides, may be purchased through most laboratory reagent distributors. For proper operation, the strips must be air-dried until the solvent evaporates and then exposed to moisture.

Removal of Peroxides (top)

If peroxides are anticipated, the safest route is to alert EHS and dispose of the material as hazardous waste. Attempting to remove peroxides may be very dangerous under some conditions. If there are a minor amount of peroxides that can be removed without causing harm, continue with one of the following methods:

1. Pass the solvent through a short column of activated alumina. No water is thereby introduced. The alumina catalyzes the decomposition of many peroxides, but it is possible that some peroxide may be retained unchanged on the column. The alumina should therefore be disposed of as a flammable material.
2. Make up a reducing solution from 60-g ferrous sulfate (FeSO4), 6 ml concentrated sulfuric acid (H2SO4), and 110-ml water. Shake the sample with this solution to remove the peroxide.

From H.L. Jackson, W.B. McCormack, C.S. Rondestvedt, K.C. Smeltz, and I.E. Viele: “Safety in the Chemical Laboratory LXI: Control of Peroxidizable Compounds”. J. Chem. Educ. 47(3): A176 (March, 1970).

Section 2c Section 2e