edited by MIRIAMC. NAQEL Avo" High Schwl
mfety tip/ Peroxides Can Be Treacherous Mlrlam C. Nagel A w n High School Awn. CT 06001
Peroxides are unstable. shock-. thermal-. and frictionsensitive compounds whose sensitivity increases with concentration. Organic peroxides are all highly flammable. High school teachers need to he aware of the possibility of peroxide formation in aging organic solvents and stored alkali metals. "A peroxide present as a contaminant in a reagent or solvent can chanee the course of a nlanned reaction" (1 . ). . That chanee can he a violent explosion. In normal oxides each oxveen - .. atom has a -2 oxidation state. In prruxidri two oxygens form a nonpolar covalent bond with a net -2 oxidation state ( 2 ) .The oxvcen linkaae (-0-0-) of the peroxy group in some o r g a n i ~ c o m p o n ~ diss actually useful when properly handled. The (-0-0-) bond splits, producing free radicals which can initiate polymerization. This instability makes them useful in polymer industries (3).But industrial settings are far removed from first year chemistry courses. Some peroxides are so sensitive they have no commercial value. Different peroxides vary in their degrees of hazard, depending on the structure of the compound and the concentration of the active oxygens. Dangerously reactive peroxides can build up in old solvents such as diethyl ether and isopropyl ether. Half-empty containers of ether can form treacherous peroxides from autooxidation. Peroxides of this type are more shock sensitive than TNT. Any purchase of ethers for use in a high school has to he ouestioned. Where the high school nee& to he especially cokerned is in the accum;lation of unwiselv nurchased solvents such as ethers. or alkali metals such as-potassium, in which dangerous peioxides could he accumulatine. Even hyd&en peroxide should he handled with extreme care, particularly the 30%solution cummonly found in high schnol labs. Hesides being il very strong oxidant, contamination oft hr H . 207 .from metals and metal ions can cause violent drcompositim reactions as large quantities of oxygen gas are aenerated. DIIUWhydrogen . - -peroxide mixed with dilutenct4c k i d forms explosive peracetic acid when heated to 110°C. Hvdrogen mixed with oraanic matter under some - - peroxide . circumstances has the same explos&e power as an equivalent weight of T N T (4). One high school chemistry teacher inherited a hottle of cyclohexene that had been in the stockroom for a t least a &cnde. The teacher, new to theschool, noticed crystals in the bottle and suspected peroxide formation. The prohlem was renorted to school authorities. After some nersuasive conversation, they t w k the prohlem seriously. A phone call to the state police was made to have the hottle removed. The police checked with chemical safety experts and were convinced of the hazard. When school was not in session. the police removed the hottle with the same care as a s&pecied bomb (5).
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"Safety Tips" presents safety information and praclical suggestions to meet the special needs of high schwl chemistry teachers. it is also a f F u m in which teachers can sharetheir experiencesand seek solutions to safetyrelated problems.
250
Journal of Chemical Education
AVO". CT 06001
On the question of possible unstahle, unwanted peroxide contamination of a reagent, one is wise t o err on the side of safety. There are tests that will detect the presence of peroxides. However (6), Any suspect material will he in some kind of container. If there is a deposit of sensitive peroxide in and around the cap ofthat container. the act of removine" the can-in order to obtain a samnle 18, test for the presence oi peroxide-may mtiate the detonation of the peroxide. This test, though reliably positive for the prescncc u i peroxide, yields undesirahlr results. Therefore, a f~rst principal pollcy statemmt: If I t h i n k 1 ought to make a test f m the presence of peroxide then I have alreadv kent it too h a : instead oftcsrinp.I should assume as certain tLat instable peroxides are presentand dispose of the material in a suitable manner. Life would he much easier if there were a list of peroxide formers and reliable information on how to store them safely. Unfortunately, the prohlem is too complex for the simple solutions. CHAS Notes (7) offers some suggestions on potential peroxide formers. One such list includes organic compounds with these structural components (examples are illustrative, not definitive): ethers, acetals, secondary alcohols, oxygen heterocycles olefins with allylic H, terpenes, >c=c' \ tetrahydronaphthalene --Hz
b-
-cH%'~
I I
isopropyl eohpounds, decahydronaphthalenes ally1 compounds
H
/y
haloalkenes, vinyls
>cs+c=c-
vinylacetylenes
\
H
I
H
I
I
44-Ar
cumenes, styrenes
I,!, 4 = 0
I
aldehydes
H
N-alkyl amides, ureas, lactams 0
H
Other compounds and elements: alkali metals potassium alkali metal alkoxides and amides sodamide organometallics Grignard reagents Regarding the prohlem of storage, as noted above, high school teachers should carefully weigh the merits of getting involved with peroxidizable reagents before ordering supplies. Does the benefit justify the risk? I t is hard to imagine any situation where a safer experiment, a good film, or even a challenging prohlem for the computer would not suffice to
teach the principles involved a t the high school level. If chemicals Drone to ~ e r o x i d eformation must be purchased, limit the order to the minimum amounts requ&ed. Then, "store peroxide formers out of heat and light in closed vessels, perferably in the container furnished by the supplier. . . [and] keep no peroxide formers on hand longer than two months"
,.
17) \.
If a high school teacher has to handle peroxides or potential peroxide formers, a few cautions for handling them should be followed (8): 1) Unused peroxides should never he returned to the container. 2) Clean up organic peroxide spills immediately with vermiculite, dilute the waste to a concentration of 2% or less, then transfer
to a polyethylene screw-top container containing an aqueous solution of a reducing agent such as ferrous sulfate. 3 ) Neuer concentrate hy evaporation or distillation. 4) Do not use metal spatulas; instead, use ceramic or wooden spatulas. This caution is particularly important for those using alkali metals.
5) Avoid all potential for friction or impact hazards. No grinding! 6) Do not use glass containerswith screw caps or glass stoppers for
storage. Use polyethylene bottles with screw caps. In a h i ~ school h lab, where the naive6 of students can make any experiment risky, peroxide proh1em.s are hest avoided by avoiding the chemicals that can produce them. Literature Cited (1) National Research Council, "Prudent Practices for Handling Hazardous Chemicals in Laboratories," National Academy Press, Washington, DC, 1981, p. 63. 12) T h m . John Amend. "General Chemistry." 4th ed., MffiraarHill Bmk Co., NBYYork, 1966,~.113. (3) Variauandi.J.,"SsfeHandlingofOrganicPeroxides."in"SafetyintheChemicalLeboratory," Vol. 3, (Editor: Steare.NormanV.), J. CHBM. EDuc..Esaton.PA. 1914,~. 11s. (0 '"H-dous Mstnials,"Ithpd.. National Fire Protection Assadstion, Boston,MA, 1972, 491M.p. 131. 15) "Safety Tips." J. CHEM.EDUC.,59,156 (1982). (6) CHAS N o w , 1141,111982). American Chemical Society, Division ofchemical Health and Ssbty, Wsahington, DC 20036. 17) Reference 16). p. 3. 18) Reference ( 1 1, p. 64.
Volume 61
Number 3
March 1984
25 1
