As many compounds can form explosive peroxides upon standing under air, it is important that these compounds be handled with care. This SOP outlines the important steps of recording the date upon opening, fixing appropriate warning labels as well as how to test for peroxides and dispose of compound once peroxides are found to be present. While not always feasible, storing compounds in the dark and under inert atmospheres can decrease the rate of peroxide formation. Please look at the list of compounds included to see if your laboratory has such compounds.
Compounds known to be susceptible to peroxide formation
Group A: Can form explosive levels of peroxide without concentration
The peroxides formed here are typically precipitates capable of producing explosive crystals without concentrating the solution. Record the date of opening, store in the dark, and preferably store in the absence of oxygen. Test for peroxides every six months and before use. Dispose of unopened containers after more than 12 months, or if a container is showing the presence of crystalline deposits, cloudiness or immiscible layers, or if peroxides are detected upon testing.
Group A Compounds
- Divinyl acetylene
- Isopropyl ether
- Potassium amide
- Potassium metal
- Sodium amide
- Vinylidene chloride
Since we cannot readily test for the presence of peroxides in solid materials such as potassium metal, potassium amide or sodium amide, it is recommended that these materials not be stored for more than three months after being exposed to air.
Group B: Explosive levels of peroxides formed by concentration
These compounds have the potential of forming explosive peroxides when distilled and peroxides in the distillation flask are concentrated. It is important to never distill to dryness. Storing these samples under oxygen also increases the levels of peroxides formed. Record the date of opening, store in the dark, and test the liquids to be distilled for peroxides every six months, and additionally test before use. Record peroxides levels on the bottle, and discard when peroxides are found where a concentration after distillation could reach 25 mg/kg.
For compounds on this list that are distilled, the risk of forming high concentrations of peroxides is much higher. For commercial undistilled samples (which will often contain radical scavengers such as hydroquinone, BHT or BHA), these compounds should be tested after the bottle has been opened for 12 months, and every six months thereafter. If a container is showing the presence of crystalline deposits, cloudiness or immiscible layers, or if peroxides levels upon testing has reached 25 mg/kg, then bring the container for disposal, and label the bottle as containing peroxides.
Compounds (e.g. diethyl ether, tetrahydrofuran, dioxane) that have been distilled away from antioxidants should be stored under an inert atmosphere and in the dark, and should be tested for peroxides every three months.
Group B Compounds
- Benzyl alcohol
- Diethylene glycol dimethyl ether
- Diethyl ether
- Ethylene glycol ether acetates
- 2-Propanol (Isopropanol)
- Methyl acetylene
- Methyl isobutyl ketone
- Vinyl ethers
- Other secondary alcohols
Solvent purification systems
If you are using the above chemicals in a solvent purification system and are not distilling over drying agents, then make sure to have routine cleaning or testing set up for your system so that accumulation of peroxides cannot occur. Make sure to keep a record of when the system has been tested or cleaned.
Old bottles or bottles not dated
For bottles of compounds listed above, where the opening date has not been recorded on the bottle, it is best to assume it is at least 12 months old and test for peroxides and record that result on the bottle along with the date tested. This should then be followed by testing every six months, and before use if this chemical is to be distilled.
If older bottles of the above chemicals are found with crystalline deposits on the cap, do not open. Also, do not attempt to force open a rusted cap. These bottles can be brought for disposal without testing, see below.
Group C: Decomposition of vinyl monomers can lead to explosive polymerization
Extended storage while exposed to air can increase the formation of unstable product leading to an explosive polymerization. Date when received and store in the dark, and preferably in the absence of oxygen. For these compounds that are stored and exposed to oxygen, the presence of peroxides should be tested every 6 months and before use. If peroxides are detected discard the chemical. If the inhibitor has been removed, then the compound should be used immediately.
Group C Compounds
- Acrylic acid
- Ethyl acrylate
- Methyl methacrylate
- Vinyl acetylene
- Vinyl chloride
- Vinylidene chloride
- Vinyl pyridine
- Vinyl acetate
*** Note that these lists are not exhaustive. You should consult the SDS of any compounds that you are working with to establish potential hazards.
Bottles of chemicals known to have the potential to produce explosive peroxide levels should have labels on the bottles warning users of this potential. This is particularly important for class A and C compounds when stored while exposed to oxygen, and to class B compounds that are to be distilled. The labels should provide an easily visible record of when the bottle was opened and when it has been last tested, including the results of the peroxide test. These labels can be generated by different labs, or are also available at Chem Stores. Bottles of THF and diethyl ether sold by Chem Stores will have these labels placed on the bottle at the time of purchase.
How to Test for Peroxides
Test strips are available for purchase from Chem Stores (ESC 109). Follow the directions on the strips, and observation of a colour change will indicate the presence of peroxides. These test strips react to different peroxide concentration, ranging from 0.5 – 25 ppm. While it is not clear which peroxide concentration poses explosion risks, other standards have pointed to between 5-100 ppm as a guide to the concentration at which disposal is recommended. It is recommended, while using these strips, that at peroxide concentrations of 25 ppm or above, the solution or container tested be discarded as waste.
Alternatively, a simple semi-quantitative test for peroxides involves mixing 1 mL of the solvent to be tested with 1 mL of glacial acetic acid in a small test tube then adding 3 drops of 5% aqueous KI. The presence of a yellow colour indicates the presence of peroxides (40-100 ppm). A brown colour indicates a much higher concentration of peroxides. A control should always be run as the test mixture will turn yellow slowly upon standing from autoxidation.
Waste disposal and Emergency Procedure
Bottles that contain liquids where peroxides have been detected, or are suspected to be present, can be brought to the Environmental Safety Facility (ESC 150) for disposal. Label the container as “waste contains peroxides”, including the concentration from above if it is known. If users are unsure of how to transport the container or are concerned about the explosive potential of the chemicals, please contact Greg Friday (x35755) for assistance.
If a spill or explosion has occurred (without personal injury to anyone), please contact Campus POLICE (x22222) to request assistance from the SPILLS team. If an injury has occurred call 911 as well as campus POLICE.
For more information
Chemical Health and Safety (1996). Kelly, R.J. Review of Safety Guidelines for Peroxidizable Organic Chemicals.