APPENDIX 4

PEROXIDIZABLE COMPOUNDS

Some ethers and conjugated olefins may form explosive peroxides during storage especially after opening of the container. This can pose a danger when these solvents are distilled. Compounds listed below are readily peroxidizable under normal storage conditions.

Aldehydes and amides, although easily peroxidized, are NOT known to accumulate peroxides to dangerous levels. Peroxidation hazards fall into three categories: A) those compounds which form explosive compounds without concentration, B) those compounds forming dangerous peroxides only upon concentration, C) monomers in which peroxides may initiate explosive polymerization. A few representative examples are listed below:

A B C

Isopropyl ether Diethyl ether Methyl methacrylate

Divinyl acetylene Tetrahydrofuran Styrene

Vinylidene chloride Dioxane Acrylic acid

Potassium metal Dicyclopentadiene Acrylonitrile

Sodium amide Decalin Butadiene

Tetralin Tetrafluoroethylene

Cyclohexene Chloroprene

Diglyme Vinyl compounds

All peroxidizable compounds should be stored away from heat and light. A nitrogen atmosphere is preferred except in the case of some inhibited vinyl monomers. Peroxidizable solvents should always be treated as though they contain peroxides. Compounds in category A should be evaluated for peroxides at least every three months. A small portion of the compound should be tested with moist starch‑iodide paper: the slightest blue coloration indicates the presence of peroxides. Compounds in category B should not be stored for more than 12 months after opening unless shown by testing to be free of peroxides. If these materials are to be retained after a positive test, they must be treated to remove peroxides, rebottled and the label redated. Uninhibited vinyl monomers (category C) should not be stored for more than 24 hours. Small quantities (<10g) containing a suitable inhibitor may be stored for longer than 24 hours only with discretion. Inhibited vinyl monomers should be stored under air rather than nitrogen.

All peroxidizable compounds should bear a proper warning label containing the date of receipt and the date on which the container was first opened. The inventory should be reviewed every three months and proper testing and disposal carried out. Before distilling peroxidizable compounds, they should be checked for peroxides and at least 10% of the volume should be left undistilled.

The following are possible methods for removing peroxides from solvents (J. Chem. Ed. 47, A175, 1970). Method 2 has the disadvantage of wetting the solvent and may leave traces of decomposition products in the solvent. Method 1. A convenient method is to pass the solvent through a short column of alumina. This may in some cases leave some peroxides unchanged on the column. The alumina should therefore be added to a dilute acidic solution of potassium iodide or ferrous sulfate before disposal. Method 2. Water insoluble solvents may be shaken with a concentrated solution of ferrous salt (60g of ferrous sulfate and 6mL of conc. sulfuric acid in 110 mL of water). Traces of aldehydes may be produced and the solvent will be left wet. For greater purity, the solvent should be shaken with 0.5% potassium permanganate followed by 5% NaOH and water.