Peroxide Formation

Organic and Inorganic peroxides are widely used in research labs due to their exceptional reactivity.  This best practice provides users information peroxide formers including an overview, hazards, formation conditions, peroxide forming categories, testing requirements, potential problems, testing and disposal.  Each laboratory using peroxide forming chemicals must maintain a standard operating procedure (SOP).  If any questions arise before using these chemicals, please reach out to the Chemical Safety Coordinator.

What is a Peroxide Former?

Peroxide Formers are chemicals that can form shock sensitive explosive peroxides over time.  Many organic solvents commonly used in labs are peroxide formers.

Typical classes of compounds that form peroxides include:

  • Ethers with primary and/or secondary alkyl groups
  • Conjugated dienes, enynes, and diynes
  • Aldehydes
  • Hydrocarbons with benzylic, allylic or propargylic hydrocarbons
  • Hydrocarbons with exposed tertiary hydrogens

Some known peroxide formers contain low concentrations of an inhibitor or stabilizer to prevent peroxides from forming quickly.

How are Peroxides Formed?

Certain conditions are needed for a peroxide former to produce peroxides:

Oxygen- Exposure to oxygen of peroxide forming chemicals will enhance peroxide formation

Time- Over time and in the presence of oxygen, chemicals will typically form peroxides due to autoxidation.  Autoxidation is the slow reaction between chemicals and oxygen.  Peroxide forming chemicals usually have a listed manufacturer date.

Heat/Concentration- The potential for peroxide formation under autoxidation increases with the application of heat or concentration.  Chemicals with previously detected peroxides should not be heated or concentrated.

Light- UV light promotes autoxidation and the depletion of inhibitors.  Oxygen is needed for autoxidation to take place.

Categories of Peroxide Formers

Peroxide formers are separated into categories depending on their tendency to form peroxides

Group A:

Chemicals that form explosive peroxides without concentration. Severe peroxide hazard after prolong storage after exposure to air.   

Storage and Testing: 

  • Unopened Container:  Dispose before Manufacturer’s expiration date if the chemical is stored properly, unopened, and frequently inspected and documented for visual signs of peroxide formation
  • Opened Containers:  Discard 3 months after opening (or up to the manufacturers’ expiration date if tested and documented every 3 months) Always test a group A chemical before use.
  • Solid chemicals:  Dispose before Manufacturer’s expiration date if the chemical is stored properly and frequently inspected and documented for visual signs of peroxide formation

Examples of group A

Butadiene*

Isopropyl Ether

Sodium Amide

Chloroprene*

Potassium Amide

Tetrafluroethylene*

Divinyl Acetylene

Potassium metal

Vinylidene Chloride

 

Group B: 

Chemicals that form explosive peroxides with concentration by evaporation or distillation, etc.  Most of these solvents are sufficiently volatile that multiple openings of a container can result in peroxide formation. Store in a dark location

Storage and Testing: 

  • Unopened Container:  Dispose before Manufacturer’s expiration date if the chemical is stored properly, unopened, and frequently inspected and documented for visual signs of peroxide formation
  • Opened Containers:  Discard 6 months after opening (or up to the manufacturers’ expiration date if tested and documented every 3 months) Always test before distilling or evaporating.     

Testing :  Test and document for peroxides every 6 months.  Always test before distilling or evaporating.      

Acetal

Butadiyne

2-Pentanol

Acetaldehyde

Dicyclopentadiene

4-Penten-1-ol

Benzyl Alcohol

Diethyl ether

1-Phenylethanol

2-Butanol

Ethylene glycol ether acetates

2-Phenylethanol

Dioxane

Furan

Tetrahydrofuran (THF)

Chlorofluoroethylene

4-heptanol

Tetrahydronapthalene

Cumene

2-hexanol

Vinyl ethers

Cyclohexene

Methyl acetylene

Other secondary alcohols

2-cyclohexen-1-ol

3-Methyl-1-butanol

 

Cyclopentene

Methyl-isobutyl ketone

 

Decahydronapthalene

4-Methyl-2-pentanol

 

 

Group C: 

Chemicals which are hazardous due to the peroxide initiation of autopolymerization.  The peroxide forming potential increases with liquids of this group.

Butadiene

Chlorotrifluoroethylene

Vinyl acetate

Chlorobutadiene

Styrene

Vinyl chloride

Chloroprene

Tetrafluoroethylene

Vinyl pyridine

Vinyl Acetate

Vinyldiene chloride

 

 

Storage and Testing: 

  • Unopened Container:  Dispose before Manufacturer’s expiration date if the chemical is stored properly, unopened, and frequently inspected and documented for visual signs of peroxide formation
  • Opened Containers:  Discard 6 months after opening (or up to the manufacturers’ expiration date if tested and documented every 3 months) Exception:  If the group C chemical is uninhibited, dispose 24 hours after use.

 

More on Safe Storage of Peroxides

  1. Chemicals that can form peroxides must be dated upon receipt from the manufacturer and dated upon opening. The CBC safety office provides stickers that research labs can use to track dates.
  2. Purchase peroxide-forming chemicals in small quantities.  Avoid prolonged storage.
  3. Purge the bottle headspace with an inert gas such as nitrogen or argon.
  4. All potential peroxide forming chemicals should be stored away from light and heat. 
  5. They should be protected from physical damage or ignition sources.
  6. Periodically test peroxide forming chemicals for the presence of peroxides.
  7. Never attempt to twist caps, move, or open bottles of liquid ethers containing crystallized materials.
  8. If containers of unknown age are found, it is highly recommended to dispose of them.

Visual Signs of Peroxide Formation

Visual inspection can assist you in determining if your chemical has begun to form peroxides.   A non-hazardous light source (flashlight) can be used to provide backlight or side light to the bottle.  Visible indicators of peroxide presence include:

  • Clear liquid containing suspended wisp-like structures
  • Precipitated crystal formation appearing like chips, ice-like forms, or a solid mass
  • Appearance of cloudiness
  • White crystal formation under the rim of the cap
  • Gross contamination
  • Visible discoloration

Note:  Solid chemicals like potassium metal, potassium amide, and sodium amide should not be tested for presence of peroxides.  Only use visual signs for peroxide formation for those chemicals.  If the solid is discolored and/or the formation of a surface crust (potassium metal forms a yellow/orange superoxide at the surface), please dispose of them.

If any of these indicators are observed, avoid additional testing or handling and contact EHS immediately.  Do not move or disturb any container if there are any questions with respect to the presence of peroxides.

Testing for Peroxides

There are a few ways to test for peroxides.  One method is to use a semi-quantitative test strip.  This may be found from outside vendors such as VWR or Sigma Aldrich.  Make sure you have a test strip that can be used with organic solvents.  Follow the directions on the package to use the test strips.  Another method is iodine detection method.  Mix 1-3 mL of the liquid to be tested and an equal volume of acetic acid in a test tube, add a few drops of five percent potassium iodide solution and shake.  The appearance of a yellow to brown color indicates peroxide formation. 

The peroxide formers above are not a comprehensive list.  Please consult the SDS for any material to inquire if it is a potential peroxide former.

 

CBC Procedure for Peroxide Formers

  1. Bottles must be dated when received in the lab.
  2. Bottles must be dated when opened in the lab.
  3. Peroxide formers should be disposed of as waste after the expiration date on the bottle or bottles class B peroxide formers can be kept longer as long as the bottles are tested and the testing is documented.  Discard upon a positive test of peroxides.   The CBC Safety Office has stickers bottles of peroxide forming chemicals.