The following classes of chemicals tend to form peroxides upon aging.

Class I

- Unsaturated materials, especially those of low molecular weight, may polymerize violently and hazardously due to peroxide initiation.

acrylic acid	styrene
acrylonitrile	tetrafluoroethylene
1,3-butadiene	vinyl acetate
2-chloro-1,3-butadiene (chloroprene)	vinyl acetylene
chlorotrifluoroethylene	vinyl chloride
1,1-dichloroethene	vinyl pyridine
methyl methacrylate	vinylidene chloride

Class II

- The following chemicals are a peroxide hazard upon concentration (distillation/evaporation). A test for peroxides should be performed if concentration is intended or suspected.

acetal	ethylene glycol dimethyl ether (glyme)
cyclohexene	furan
cyclooctene	isopropyl benzene
cyclopentene	methylacetylene
diacetylene	methylcyclopentane
dicyclopentadiene	methylisobutyl ketone
diethylene glycol dimethyl ether (diglyme)	tetrahydrofuran
diethyl ether	tetrahydronaphthalene
dioxane (p-dioxane)	vinyl ethers

Class III

- Peroxides derived from the following compounds may explode without concentration.

divinyl ether	potassium metal
divinyl acetylene	potassium amide
diisopropyl ether	sodium amide
1,1-dichloroethene