Peroxlde T e a Results
Compourd
NumRedox ber KI Strip Test Of SOIW P P ~ S a m lion Meth- Perplesa Test cd oxide
Alcohals, primary Ethanol l-PropanoP I-Butamla l-Butanalb 2-Melhylpropanolb l-Pentanolb 3-Methyl-l-butanol 3-Methyl-l-butan01 3-Methyl-l-butanol 3-Methyi-l-butanol 3-Methyl-l-butanol 2-EthyC1-bUanol l-Heptanol l-Octanol CyClopr~pyI~~rbin01 4-Penten-1-01 2-PhmylethanolS 1 2-Phenylethanol 1 2-Methoxyelhanol 1
Compound Cyciopentanol Cyclopenlanol Cyclahexsnol Cyclahexanol Cyclohexanol 2.3-Butanedial
Num Redox bw Ki Strip Test or so1uP P ~ S a m lion Melh- Perplesa Test od oxide 1 1 1 2 1 1
t t t -
C C 8 B 8 C
0 3
0 3 8 0
AlrohoIs, tertiary. a~ylili,or benzyll
-
1 t&Butyl alcohol3 2 tert-Amy1 alwhol 3-Ethyl-3-pentan01 1 2-Cyclohem-1-01" 1 t Benzyl alcoholo 1 BenzyiaI~~holV Benzyl alcoholb 1 t Benzyl alcohol" 1 l-Phenyiethanolc 1 t
+
+ +
t t
-
B B C
10 12 0
Alcohols, seconda'y
C B B B B B B B B
0 0 0 30 20 32 40 100 30
Num-
Redox Ki Strip Test 01 Sol* P P ~ Sam- tion Meth Perplesa Test cd oxide b%r
Compound Ethsrs Diethyl ether Dielhyl etherk Dlbutyl ether Dibenzyl ether Tetrahydrofuran Tetrahydrofuran TelrahydrOlurM l.4.Oioxane 1.4-Oioxane Cyclohexene oxide AM* Acetaldehyde lsobulyraldehyde Heptaldehyde0
Kemnes
Ethylbenzeneb ~(hylbenzene"
l l
+ +
6
B B
8
Acetoneb 2-Warnb 2-Pentanone
2 2 2
i
-
C C - 8
0 0 2
?-Pentanone ?-Pentanon$ 3-Pentanone 3-Pentanone 3-Pentsnone +Methyl-2-pentanone PlnacoioneD 2-Heplanone 3-Heptanane Cyclopentanoneb Cyciopentanoneb Cyclohexanone Cyclohexanone 2-Cyclahexenel-one
Alkanes 1-Pentene 1-Pentane 1Pentene t-Octene l-Octene 1-Octene Cyclohexene Cyclohexenee 1-Methylcycb hexI-Methylcydohexene 3-Methylcyclohexene 4-Methylcycb hexene (+)-Limonsne lndene 'Number of IndIvMual bonlsr tested. lUsed as unknown in Llnstromberg. W. W.: Eaumganen. H. E. Organic EXperImenh,6th ed.: Math: New Yoh. 1983 year Old. 'Estimated to be 10 years old, W e r Analyzed Reagem Grade, bonle anosvaner fllled. 'Yew old. '~abhedas lrsfhylisobvhllcarbiM: therefore, ignored by storeroom personnel 'Labeled as di-npropylcarbinol. Dmree 016. 'Bonk dated 19m lSdf1e dated 1977. *Bonk dated one monm before mandatory dispad date.
arrival and to dispose of outdated samples. However, the dating o f other chemicals i s more sporadic; and we found t h a t such dati n g could n o t be trusted, as occasionally small bottles were used as dispensing battles, being refilled periodically f r o m larger stock bottles. Nevertheless, it was obvious that age is an important factor in determini n g the peroxide content in the chemicals tested. Exceptions were benzyl alcohol, 1and 2-phenyletbanol, a l l of which seem t o develop peroxides rather rapidly. In those
instances o f alcohols t h a t appear n o t t o have formed peroxides, it is possible, even probable, that our samples were simply too young t o have had time t o form ~eroxides.We believc that all primary, wcondarv, and nllylic-brnzylic alcuhols should Ire treated as if r h r y nrp likely ro form p e r m i d r s on stand. ing
teaching laboratory storeroom are likely t o b e purchased in quantity and k e p t for severa l years as a matter of economics and convenience. Thus, often we were unable t o get a positive test for peroxides in a sample taken from a bottle in the research laboratory but h a d n o difficulty finding a sample that would test positive in the teaching laborato-
Some observations n o t obvious f r o m the information in the table are the following. As might be expected, chemicals in the
(Continued o n page A228)
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Volume
65
Number 9
September 1988
A227
ry stockroom. Chemicals hearing unusual (but correct) names were less likely to be used by storeroom personnel than those hearing IUPAC names. For example, an old sample of methylisobutylcarbinol with a peroxide content of 30 ppm stored along with a fresher, peroxide-free bottle of 4methyl-2-pentanol. Even in the research laboratory, current safety practices may discourage the use of certain solvents, such as dioxane; thus, they may stand for some time accumulating peroxides. Purification of those substances that gave positive tests for peroxides was accomplished for all classes of compounds by passing the substances through a column of activated alumina or for water-insoluble compounds by washing the substances with acidified ferrous sulfate or with 20% aquebv Jackous ~otassiumiodide as sueeested .... *on et nl. 1.4). It was important to rrtrst the purified sulatances fur peruxidrs, parfirulnrly when purification by passage rhruwh alumina was used with substances having relatively high peroxide content, for occasionally one pass was not adequate to remove all of the peroxide. In some instances the use of acidified aqueous ferrous sulfate or with 20% aaueous ootassium iodide as s u a ~ e i t e dl,y Jarkson rr al vQ,. It wns rmporrant to retest the purified ruhstances fm peruxidrr, particularly when purification try passage through alumina was used with substances having relatively high peroxide content, for occasionally one pass was not adequate to remove all of the peroxide. In some instances the use of acidified aqueous ferrous sulfate or aaueous ~otassiumiodide wns not only the morecurt r f f r r t i \ r bur also the mure rapid method or purificarion.
.
Conclusions To the classes of peroxidizable compounds listed by Jackson et al. (8) should be added the primary and secondary alcohols, the allylic-benzylic alcohols, the ketones, and, possibly, the aralkanes with benzylic hydrogens. Nothing said here diminishes any of the conclusions and recommendatians made by Jackson et al. (a), and their recommendations should continue to be observed with possibly the following additions or amendments. First, we believe that all chemicals used in the laboratory should be dated by the prouider, preferably with the date of manufacture but, a t the very least, with the date of packaging. Since the purchaser has no way of knowing how old the Durchased material mav, be.. the burden for dating should fall on the seller. lfarhrmicnl ia not dared hy rhp manufacturer or supplier, it rhuuld hp dated on receipt by theresearch or teaching laboratory personnel. Neat, we recommend that all peroxidizable substances be tested immediately before any use, not just heating or distillation, especially in the teaching laboratory where they will he handled by relatively inexperienced personnel. Jackson et al. (8) recommend that all peroxidizable chemicals be tested 12 months after receipt and, if found positive, be purified or disposed of. For
.
A228
Journal
of Chemical Education
some peroxidizable chemicals 12 months may be too long. We recommend, especially in the teaching laboratory storeroom, that all chemicals be labeled with their IUPAC names in a uniform manner, even if this requires adding a name to that provided by the supplier. We recommend also as a general safety practice that both teaching and research laboratories purchase all chemicals in amounts that will be consumed within 12 months. Finally, it should be noted that we have not performed the ultimate experiment, a detailed examination of the behavior under distillation of the alcohol samples that gave ~ a s i t i vtests e for ~eroxides.Thus, the observation that alcohols may contain peroxides does not prove that such peroxides have been or will be the causes of explosions occurring during distillation. Very probably operator error is a contributing factor. However, i t also probable that some explosions occurring during distillation that have been attributed solely t o operator error (and, therefore, not reparted to the chemical community) may have been compounded by the presence of thermally unstable contaminants. One common but cardinal sin in distillation is the carrying out of a distillation too close to dryness. Understandably, both students and research workers want to squeeze the last drop of product out of every separation. Probably we should require heginning students, a t least, to stop distillations after about two-thirds of the initial volume has distilled. Experimental Detection of Peroxides (a)Potassium iodidesolution. To 1mL of a 20% by weight of aqueous solution of potassium iodide was added l mL of sample in a small test tube. After vigorous mixing and shaking a change of color in the aqueous layer from colorless to yellow was taken as an indication of alow levelof peroxide in the sample. A brown-red eolor was taken as an indication of high peroxide eantent. If no color change was observed, peroxides were considered to be absent. (b) Peroxide test paper. Method A, for volatile ethers. A peroxide test strip' was immersed for about one second in the samole. Then the reaction zane was breathed upon gently t'urn p e r ~ l o about f I5src~mli. TIw reaction zone was then compared with the colur irnle prowded fur usr with urcmii solvents to estimate the peroxide eantent in ppm. Method B, for nonualatile ethers, water-immiscible compounds. A measured amount of the sample was mixed with three times that amount of peroxide-free ether. The solution was tested as in Method A. The ertimntpd nmwnt of prroxide rend i n m the colorsr~lewasmultiplied h) 4 rororrect for ~hcnddtclerher..MzrhodC,fort
