graded. The notebook grade, which is a substantial part of the lab made. is based on format. claritx observations, and allows for comple&nes~.The advance studknt short, easily graded lab reports.
A Microscale Purification and QualitativeSpectroscopic Examination of Cw (Buckminsterfullerene) An Experiment Suitable for Undergraduate Organic Laboratofy Courses
The Micmscale Lab Report
Because most of the traditional information called for in the lab report already has been entered in the lab notebook, it need not be repeated in a lab report, so a short report is written on a 5 8 index card. Atypical report has a n equation for the reaction, significant observations, and datasuch as melting or boiling points, and can be prepared quickly and easily by students during the last 10 minutes of the class. The reports are ready to hand in as students leave for the day, so that lab reports are never late! These reports are much less timeconsuming to grade, resulting in a tremendous time saving for the instructor faced with grading 70-80 lab reports a week. The essential information is written only once in the lab notebook, and lab reports are simply a summary of the completed work.
x
Shorter Lab Experiments
One oftbe trademarks of a traditional organic chemistry lab is a frantic scramble to finish the lab in the allotted time frame. A typical 3-h lab often seems to be planned so that an average student can finish the lab in 3 l/Z b. Students may begin the lab by watching a solution reflux for an hour. but invariablv end the lab bv rushine to finish the final sLps in a pmce&re just as class eudsr~ecausemicmscale labs typically require less reaction time, lab experiments are shorter, but this often leads to a tendency to do many more experiments during a term. It seems more sensible to plan a lab that an average student can complete in 2 lD h. The 30-min leeway allows students some time to think about what they are doing, recover from a mistake, prepare their minoscale lab report and, of course, leave the lab on time. The lab becomes a much less stressful place for both the instructor and the student. Students are more likely to leave the lab with a feeling of success and accomplishment. The lab atmosphere is more relaxed, and some students may begin to see the fascination that lab work holds for most chemists. The strateeies above have ~ m v e dsuccessful at Cortland and dowedous to modernize the organic laboratory proeram and imomve the lab atmosohere. both ohvsicallv and socially It L o u r hope that they will be usifil for r h e r s who plan to change their organic chemistry laboratory programs.
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LiteraturnCited 1.HcUer. R E J. C. S. T 197S.8.231. M.J. C 9 T.Is80 19, 190.
2. Picks*.
' Author to w h m correspondence should be addressed. me crude soot should be handled with care because potentially toxic aromatic byproducts may be present. If an HPLC is available, the actual ratio can be determined. We used a 25 cm x 4.6 mm Du Pont Zorbax 5 Silica Gel column with hexane as eluent. Flow rate was 0.75 mL /min with UV deteaion at 260 nm. The fullereneselute in order of increasing molecular weight.
James F. ~arecek'and Scott D. Kuduk
State University of New York Stony Brook, NY 11794
Since their first preparation in 1985 (1,2),interest has continued unabated in the family of closed cages of carbon atoms known as fullerenes. One of the difficultiesin working with these compounds is obtaining macroscopic a simple amounts of pure materials. This article and inexpensive purification procedure, which can be used in an undergraduate organiclaboratory course, for isolating the most common member of the family, Cm fullerene. The purification is based on a recent report by Scrivens and 'Jbur (3)that uses activated carbon as the separation medium. If instrumentation is available, IR, UV,and 13CNMR spectra can be conveniently obtained. Crude fullerene-containing graphitic soot can be prepared by methods previously described in this Journal (4, 5) or can be purchased fmm a number of sources (Texas Fullerenes, Strem, etc.).' The crude soot usually contains about 5% fullerenes by weight. If an ultrasonic cleaning bath is available, the fullerenes can be extracted conveniently by suspending the soot in toluene (1 g I50 mL) and sonicating at mom temperature for an hour. The mixture is filtered under reduced pressure through a pad of Celite and the solid washed with toluene. The burgundy-colored fdtrate is evaporated to dryness on a rotary evaporator at 40 "C leaving a black solid. If a sonicator is not available, the soot can be placed in an extraction thimble and extracted with toluene in a Soxhlet apparatus for 3-4 h. Evaporation of the toluene affords the crude fullerene mixtll?~
The solid obtained (usually 30-40 mglg of crude soot) is washed bv swirling twice with ether ( 5 mLI 20 me: of solid) to remove any grease and ether soluble hydrocaTbon side pmduds. The solid is finally dried under reduced pressure to remove residual ether. The fullerene mixture at this point usually contains 8590% Csowith the remainder being mostly C,o and traces of higher fullerenes. The actual composition depends on the source of the sooL3Astock solution can be prepared for 20 students by dissolving the crude extract in toluene (30 mg/ 10 mL).The solution is stable for at least several weeks if stored in the dark. The separation of Cm from the other fullerenes may be conveniently done using a 5 314411. disposable glass Pasteur pipet as a column. A plug of cotton is placed in the bottom and covered with a thin layer of sand. The column is packed with a slurry prepared fmm 0.2 g of Silica Gel 60 (flash silica) and 0.1 g of activated carbon in toluene. This eives a 2.5 x 0.5-em column bed. Norit A activated carbon from several different sources gave good results. About 0.5 mLofthestmk fullerenesolution (1-2 meofcrude extract) is applied to the column, and the solvencis drained to the top of the bed. The column is then eluted with toluene.
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Volume 71 Number 6 June 1994
the microscale laboratory Fractions of 0.5mL are collected in small test tubes or vials. If desired, the flow rate can be increased by applying pressure using a small pipet bulb with caution that the column packing is not sucked back into the bulb. The magenta colored Cso solution is colleded in two to three fractions. Only Csoelutes from the column. The higher fullerenes remain on the column under these conditions. A simple way to obtain an infrared spectrum is to evaporate the material onto a KBr disk to form a film;4however, evaporating directly from the eluate gives background toluene absorptions.Abetter procedure is to transfer a few drops of the eluate to a small vial and evaporate to dryness using a stream of N2. The material is redissolved in carbon disulfide (HOOD), and this solution is applied to the salt plate dropwise until a mustard colored film of the desired thickness is deposited. Agentle stream of N2 is blown over the plate to remove as much of the residual solvent as possible. The four sharp fullerene absorptions at 1429,1181, 576,and 527 cm-' (6) are observed easily. There may be an absorption a t 1500 an-' from residual CS2, but this does not interfere with the fullerene spectrum. When no longer needed, the film can be washed off the plate with a few drops of toluene. To obtain a UVIvisible spectrum, a drop of the toluene solution is placed in a small tube and the solvent blown off with Nz. Enough hexane to fill a cuvette is added and the mixture allowed to stand a few minutes with occasional shaking. Enough of the fullerene dissolves in the hexane to allow a spectrum to be obtained directly. There are strong absorptions at 213,257,and 329 nm with a weak band at 404 n m (7). If an FT NMR spectrometer with a carbon channel is available, a spectrum can be run taking advantage of the recent observation that fullerenes are quite soluble in 1,2dichlorobenzene (8, 9).For an NMR the separation needs to be run on a larger scale or with several student samples pooled to obtain 5-10 mg of material. This is dissolved in 0.4 mL of dichlorobenzene and about 10 vol % of deuterobenzene added for an internal lock. A13C spectrum can be obtained in about two hours. Cso fullerene has a single peak at about 143 ppm. The much larger dichlorobenzene %se of KBrdisks is mandatory. NaCl disksabsorb strongly and cut off the two lowest wavenumber fullereneabsorptions.
peaks are further upfield a t 132.6, 130.5,and 127.7 ppm and do not overlap with the fullerene peak. Acknowledgment
This experiment was developed as part of a project to establish an Undergraduate Instrumentation Center, supported by the National Science Foundation Instrument and Laboratory Improvement Program under grant DUE 9150974. Literature Cited
1. Kr0to.H. W.:Heath,J.R.;OBlien.S.C.:Curl,R.F;Smdey,R.E.NoNm 1965,318, 162-1M. 2. F a an histoticel review by oneof the diezoverersofhuerenes see: Kmta.H. W AM. Cham k t . Ed. Engl. 1882,91,111-129. 3. Smlvena, W. A,; Bedworth P V; 'Ibw J. M. J. Am. Cham. Sor 1992,114,7917-7919. 4. lawe, D.W.; Potter,W T.;Teeters, D. J Chem. Edue. 1882.69, 663. 5. Craig, N. C.; Gee, G. C.; Jahn8an.A. R. J. Chem. Edvc 1SSZ. 69,66P668.
6. Cor,O.M.;Behal,S.;Diako,M.;Crmn,S.M.;Crpaney,M;Hsu,C.S.;Kollin,E.B.; Mil1ar.J.;Robbina. J.; Robbins, W.;Shed.R.D.;?indall.P. J.Am. Chom. Soc. 1891,113.2940-2944. I. H a , J. P; Kmto, H. W: Taylor, R Chrm. Phys. h t t . 189l.177,S9P397. 8. 8etivens. W.A.:Ibur, J. M. J. Cham. Soc.,Cham. Commun. 1895,1207-1209. 9. Ru&, R. S.; B e , D. S.; Malhoha, R.; Lments, D.C. J. Ph? Cham 1992.97.3315L 3383.
Microwave Synthesis of Tetraphenylcyclopentadienone and Dimethyl Tetraphenylphthalate John W. Elder
Fairfield University Fairfield. CT 06430 A recent paper (1)has reviewed the advantages and some of the applications of the use of microwave heating in the organic laboratory. We have found that microwave heating is useful in the synthesis of tetraphenylcyclopentadieneoneand dimethyltetraphenylphthalate, a sequence that appears in whole or in part in many organic laboratory books (2). The microwave method in both the condensation and Diels-Alder reactions is not only faster but also much simpler to perform and gives products of high purity without a complicated work-up. The microwave oven used was a Sharp Carousel I1model R-4A73.Five to 10 reactions were run simultaneously. (Continued on page A144)
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Journal of Chemical Education
