overhead projector
edited by DORIS KOLB Bradley University Peoria. IL 61625
Oxidation of Cyclohexanol-An Amoebalike Reaction
A Diels-Alder Reaction for the Overhead Projector
Kenneth E. Kolb' and Doris Kolb Bradley University Peoria. IL 61625 A reaction that is chemically, physically, and visually interestine involves the oxidation of cvclohexanol. A Petri dish about &-third fullofacid dichromatesolution ( 2 g KjCr20ner 100 mL H,Owith 10 mLconc. H.,SO, added) is daced on , by one, four to the stage of & overhead projector. ~ h e done six drons of cvclohexanol is added to the aqueous dichromate ~ o l u t i o n ~ ~ i t10-20 h i n s the previousliclear drops of cvclohexanol mow quite visible as they become oxidized and emulsified an> hence opaque to transmitted light. These droplets exhibit a lively, rhythmic contraction and expansion, which is clearly seen by the overhead projection. This pulsation in shape and size seems t o result from the cyclohexanol becoming partially oxidized to cyclohexanone and the resulting droplets changing shape t o adjust their surface tension to the chaneine ratio of cvclohexanol and cvclohexanone present. The amoebalike reaction continues for several minutes. so there is time available for having the class sveculate on &hat is occurring in both the chemical and phisical sense.
Kennelh E. Kolb' Bradley University Peoria, IL 61625 The Diels-Alder reaction, key organic reaction, can he easily demonstrated t o a lecture class by reacting the strong dieno~hiletetracvanoethvlene (TCNE) with anthracene as the dfene. One way to carry out the readion is to pour 8 mL of a clear. colorless saturated solution of anthracene in cvclohexane into a 30-50 mL beaker on the stage of an oveLhead projector. Then, using a standard medicine dropper, add a squirt (-0.8 mL) of a saturated solution of TCNE in dichloromethane. Upon this addition the fleeting (hut easily seen) vivid dark green color of the charge-transfer complex is observed. A total of 5-6 squirts of the TCNE solution is added, with the transitory green color being seen after each addition, but fading more slowly each time. If the clear reaction solution is then allowed to stand for several minutes, crystals of the Diels-Alder product of TCNKanthracene start to appear. Swirling the beaker helps inviewing the first crystals formed. Within a 1 0 min crystal formation is complete and the mixture becomes completely opaque with the Diels-Alder adjunct of TCNE t o anthracene.
' Work done at the Institute for Chemical Education at the Universi-
Work done at the Institute for Chemical Education, University of Wisconsin at Madison.
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ty of Wisconsin at Madison.
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Volume 66
Number 11 November 1989
955
