PEROXIDE-FORMING CHEMICALS

Transcription

1 XVIII. PEROXIDE-FORMING CHEMICALS Some common laboratory chemicals can form peroxides on exposure to air. Peroxides are shocksensitive and can be violently explosive in concentrated form or as solids. Others can result in rapid polymerization and can initiate a runaway, explosive reaction. The most commonly used peroxide-forming chemicals are diethyl ether (ethyl ether), tetrahydrofuran (THF), dioxane. Isopropyl ether (diisopropyl ether) is a severe peroxide hazard. Organic peroxides are another class of compounds with unusual stability problems and as such are one of the most hazardous classes of chemicals normally handled in the laboratory. Due to the unstable nature of organic peroxides, it is necessary to contact the Environmental Health & Radiation Safety (EHRS) at prior to discarding these chemicals. STORAGE PROCEDURES The best way to manage chemicals that have the potential for forming shock sensitive peroxides is to purchase only the quantity that is needed for one month use. Store the material in a tightly closed, properly labeled container in a flammable storage cabinet, away from flames, heat, sources of ignition, light, oxidizers and oxidizing acids. Caution: All peroxidizable compounds should be stored away from heat and light. They should be protected from physical damage and ignition sources. When peroxide-forming chemicals reach their expiration date, it is recommended that you process the chemicals for waste collection. If peroxide concentrations are greater than 80 ppm, call Environmental Health & Radiation Safety at (215) (see Testing Procedure section below). If a peroxide forming chemical is older than its expiration date or is stored longer than the time limits (see Common Peroxide-Forming Chemicals below), follow these procedures: Prior to moving the container, examine it. Call EHRS if crystals are visible in the chemical solution or if crystals are on or in the container. Closely examine the container near the cap for the presence of crystals. Some peroxide crystals in solution have a very fine, spun glass-wool appearance. o Do not test compounds for peroxides if it crystals are present, let EHRS personnel manage these containers? Call EHRS if the container has a metal screw cap. Do not open the container. Call EHRS if the container has been stored longer than two years. Leave the container where it was found until EHRS staff arrives

2 If the container was picked up gently put it down in a safe place. Do not shake the container or place it near sources of heat or ignition. Tape-off the area containing the potentially shock sensitive compound and warn laboratory personnel of its presence. TESTING PROCEDURES Routinely test the chemical on a monthly basis, after its expiration date, for peroxide formation. NOTE: The testing of chemicals for peroxide formation must be performed by qualified individuals. If you determine the container is safe to open: Test the peroxide-forming chemical with a commercial test strip. Commercial test strips have a test range of 0.5 to 50 ppm (mgl) or 3 to 100 ppm. If peroxides are greater than the concentration range measured by the test strip, a serial dilution with deionized water is necessary to determine a semi-quantitative concentration of peroxides. The following concentration guidelines apply: If: Then: Less than 80 ppm peroxides Solution is okay for use 80 ppm to 400 ppm Call EHRS for packaging and removal Greater than 400 ppm Call EHRS, who will contact an approved vendor or if necessary the Philadelphia Bomb Squad Commercial test strips: Purchase from: Baxter Scientific Products, , Matheson Scientific, , Spectrum Chemical, , Thomas Scientific, , and VWR Scientific, Product name: EM Quant Ion Specific Test Strips, Peroxide Test: mgl Catalog number and price: EM , Pk.100$ Product name: Baker Teststrips, Peroxide (H2O2): mgl. Catalog number and price: JT4416-1, Pk.100$ (Prices subject to change. Equivalent test strips from other vendors are also acceptable.) Alternate Peroxide Test: The procedure listed below only indicates the presence of peroxides and does not indicate their concentration. To 10 ml of a 20 percent aqueous solution of the unknown add: Small spatula of sodium iodide or potassium iodide Five ml of distilled water Five ml of organic solvent (methanol or ethanol) A few drops of concentrated hydrochloric or sulfuric acid

3 An instant color change indicates the presence of peroxides yellow to faint orange = negligible amount of peroxides purple to dark violet or brown peroxides present If this procedure indicates a dark violet or brown color, call the EHRS for packaging and removal. PEROXIDE INHIBITOR If any peroxides are detected, a "dash" of butylated hydroxy toluene (BHT) should be added to the container to inhibit further peroxidation. Chemicals containing less than 80 ppm peroxides should have the BHT added, unless it is determined that the inhibitor will adversely affect experimental work. WARNING LABEL A warning label should be affixed to all containers of peroxidizable compounds, as illustrated below, to indicate the date of receipt and the date the container was first opened. PEROXIDIZABLE COMPOUND Date Received Date Opened Discard or test within months after opening (circle one) EMERGENCY DISPOSAL The EHRS will have a University approved vendor or the Philadelphia Bomb Squad to remove any containers of peroxide forming chemicals if: the chemical has a peroxide concentration of greater than 400 ppm, the container has crystals in or on it the container is metal with a metal cap, or the chemical is suspected to be shock-sensitive due to its age. COMMON PEROXIDE-FORMING CHEMICALS Types of Chemicals That Are Prone To From Peroxides A. Organic Substances(in approximate order of decreasing hazard) H

4 1. C-O- Ethers and Acetals with a hydrogen atom H 2. C=C-C Olefines with allyic hydrogen atoms. X 3. C=C- Choloroolifines and fluoroolifines atoms 4. CH 2 =C Vinylhalides, esters and ethers 5. C=C-C=C Dienes 6. C=C-C=CH Vinylacetelens with a hydrogen atom 7. C-C=CH Alkylacetelens with a hydrogen atom 8. C-Ar Alkylarenes that contain tertiary hydrogen atoms 9. -C-H Alkanes and cycloalkanes that contain tertiary hydrogen 10. C=C-CO 2 R Acrylates and methacrylates 11. C-OH Secondary alcohols O 12. -C-C Ketones that contain a hydrogen atom H 13. -C=O Aldehydes carbon atom O 14. -C-N-C Ureas,amides and lactams that have a hydrogen atom on a attached to nitrogen B. Inorganic Substances:

5 1. Alkali metals, especially potassium, rubidium and cesium 2. Metal amides 3. Organometallic compounds with a metal atom bonded to carbon 4. Metal Alkoxides. SEVERE PEROXIDE HAZARDS ON STORAGE WITH EXPOSURE TO AIR Discard within 3 months Diisopropyl ether (isopropyl ether) Divinylacetylene (DVA) Potassium amide Potassium metal Sodium amide (sodamide) Vinylidene chloride (1,1 dichloroethylene) Peroxide Hazard on Concentration Do Not Distill or Evaporate Without First Testing for the Presence of Peroxides Discard or test for peroxides after 6 months Acetaldehyde diethyl acetal (acetal) Ethylene glycol dimethyl ether (glyme) Cumene (isopropylbenzene) Ethylene glycol ether acetates Cyclohexene Ethylene glycol monoethers(cellosolves) Cyclopentene Furan Decalin (decahydronaphthalene) Methylacetylene Diacetylene (butadiene) Methylcyclopentane Dicyclopentadiene Methyl isobutyl ketone Diethyl ether (ether) Tetrahydrofuran (THF) Diethylene glycol dimethyl ether (diglyme) Tetralin (tetrahydronaphthalene) Dioxane Vinyl ethers Hazard of Rapid Polymerization Initiated by Internally Formed Peroxide a a. Normal Liquids; Discard or test for peroxides after 6 months b Chloroprene (20chloro- 1,3- butadiene) c Styrene Vinyl acetate Vinylpyridine b. Normal Gases; Discard after 12 months d Butadiene c Tetrafluoroethylene (TEE) c Vinylacetylene (MVA) c Vinyl chloride a Polymerizable monomers must be stored with a polymerization inhibitor from which the monomer can be separated by distillation just before use. b Although common acrylic monomers such as acrylonitrile, acrylic acid, ethyl acrylate, and methuyl methacrylate can form peroxides, they have not been reported to develop hazardous levels in normal

6 use and storage. c The hazard from peroxides in these compounds is substantially greater when they are stored in the liquid phase, and if so stored without an inhibitor they must be considered a Severe Peroxide Hazard on Storage with Exposure to Air. d Although air will not enter a gas cylinder in which gases are stored under pressure, these gases are sometimes transferred from the original cylinder to another in the laboratory, and it is difficult to be sure that there is no residual air in the receiving cylinder. An inhibitor must be put into any such secondary cylinder before one of these gases is transferred into it; the supplier can suggest inhibitors to be used. The hazard posed by these gases is much greater if there is a liquid phase in such a secondary container, and even inhibited gases that have been put into a secondary container under conditions that create a liquid phase must be discarded within 12 months