edited bv
ARDENP. ZIP; SUNY-Conland
the microscale laboratory Converting to a Microscale Laboratory with lmprovised Equipment
A Summary of Previously Published lmprovised Microscale EquimentKechniques Apparatusflechnique Test tubes as reaction vessels/ air condenser Micro-stir bars from paper clips Pasteur pipet microstill Microscale Kugelrohr distillation Recrystallization Filtration Chromatography columns Pressurized gas sources for column chromatography Heating baths Sublimation NMR Microcells
R. David crouch' Department of Science and Mathematics Coker College Haftsville, SC 29550 Todd D. el son' Fort Collins, CO 80523 Chris M. inter^ Division of Radiation Health Services Department of Environmental Health Sciences The Johns Hopkins University School of Hygiene and Public Health Baltimore, MD 21205
In recent years, the advantages of converting traditional chemistm laboratorv exoeriments to microscale have been noted with increasGg frkquency (1-5). But, the expense of rapidly converting an entire course to microscale remains, perhaps, the biggest barrier to its widespread acceptance. Larger Scale to Smaller Scale As a n alternative to remaining with the traditional, larger scale laboratory approach, much of the equipment required for microscale reactions can be improvised using materials already present in most labs or equipment that can be purchased a t low cost. Many ofthese low-cost alternatives have been described in various publications as summarized in the accompanying table while others have been ~ a s s e dalonn bv word-of-mouth. To the best of our knowiedge, a sgene;aliisting of such improvised equipment does not exist. It is our h o ~ that e this DaDer will serve as a source for those wishing to convert t h e i r laboratory courses to microscale as well as to stimulate an interest in the development and reporting ofadltional materials for the "improvised" microscale laboratory. Commercial Reaction Vessel Typically, organic reactions on microscale levels are performed in commercially available reaction vessels such as 14120 ronnd-bottomed flasks and heaw-walled ' V s h a ~ e d vials. An inexpenslvc alternatlvc that i a s proven larlv useful is a one-dram ODII-clear elass vial. lfan mcrt atn;osphere is required, a rubber septum designed for use with 19122glassware fits tightly over the outside of the vial and an inert gas introduced into the vessel via a disposable syringe needle inserted into the septum. If a larger volume than the one-dram vial allows is required, a two-dram vial can be similarly fitted with a septum designed for 24/40 glassware. Although the inert gas source may be a pressurized tankhubbler assembly, less expensive is the use of
'Author to whom corresoondence should be addressed. 2Currentlya post-doctoial fellowin the Department of Chemistry at Colorado State University. 3Currently a post-doctoral fellow at The Johns Hopkins University School of Hygiene and Public Health.
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Reference 6
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9 10, 11 12, 13 14
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balloons mounted on disposable Plasti-pak syringe barrels to maintain an inert atmosphere. A more durable and, thus, less likely to burst substitute for balloons is a rubber Pasteur pipet bulb. The absence of a ground glass or threaded joint would seem to limit the utility of this reaction vessel. However, the rubber septum can be used to make many of the same connections of a ground glass or threaded joint. A disposable Pasteur pipet can be inserted through a puncture in the septum. Once inserted, the narrow, tapered end is cut offto give a straight glass tube through the septum. When a&ed to the vial, the cup formed by the rubber septum can be filled with chipped ice and the solvent vapors will rapidly cool upon contact with the glass wall, allowing refluxing of the reaction mixture. For high boiling solvents, the tube can act as an air condenser. Rotary Evaporation Concentration of samples via rotary evaporation also is possible using this rubber septum method of attachment. Place a rubber septum designed for use with 10130 joints inside the one-dram vial and insert a disposable 20-gauge needle into the septum. The large end of the septum will fit over the male end of a 24140-to-14120 glass adapter, allowing solutions in the vial to be concentrated on the rotary evaporator. A two-dram vial can be connected using a septum designed for 14120 glassware. Recrystallization The separation of solids from liquids is key to the successful purification of solids by recrystallization and the Erratum An error occurred in the article by Moses Lee which appeared in this column on page A155 of the June issue. The correct structure for the diastereomer 29, shown in Figure 1, should have the D and H atoms reveresed.
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Volume 70 Number 8 August 1993
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the microscale laboratory drying of organic liquids. Traditionally, such separations have been achieved by filtration. Filtration can be achieved by withdrawing the liquid through a syringe fitted with a disposable syringe filter between the syringe barrel and the needle. This method is useful when either the liquid or the solid is to be isolated. If only the liquid is of importance (in the case of drvine . a solution with MeSO*. -. for e&nple), simple filter can be prepared by cutting off the top bulb of a plastic Beral-tvue ~ i ~and e t~ a c k i n ethe neck &th cotton,'glass wool, or a small piece bf Kimwipe and Celite. The remainder of the bulb provides a larger volume than the filter prepared from a disposable Pasteur pipet.
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Column Chromatography One of the more popular methods of isolating oreanic compounds is column Ehromatography. ~ i c r o s c a Lcoiumn chromatography allows for good separation of products from reaction mixtures. A co~umncan be easily by packing a modified plastic Beral-type pipet with silica gel and allowing the mixture to elute using a supply of pressurized gas. The opened bulb of the pipet provides a reservoir for the eluting solvent. Heating devices can be prepared easily and inexpensively from materials already present inmany labs. Acrystallizing dish filled with sand and placed on a hot plate provides a eood heat source. An alternative to the fraeile &ass contarner is to fill a heating mantle with sand. Silicone oil baths also are prepared easilv usine a crvstallizine dish or a beaker for deep& baths. he hea%ng k~ement prepared bv coiline a piece of 16- or l&eauee Nichrome k r e around a pen& a i d placing the loop in the bottom of the vessel with the ends of the wire extending from the liquid for connection to a Variac. A paper clip in the bottom of the bath that rotates when daced on a stir motor ensures mixing of the liquid and-a more uniform temperature. The temperature of either of these baths can be monitored by placing a thermometer in the sand or silicone oil, and these heat sources will accept various sizes of glassware. Although lacking the sophisticated look of commercially available microscale equipment, these pieces of alternative equipment and those cited in the accompanying table allow for the slow phasing-in of expensive materials. The numerous immediate advantages of microscale laboratory exercises can be realized without the high initial costs.
11. leporterie, A. J Chem Ed=. 1992,69,A42. 12. BeUetire,J. L.; Mahmoodi, N. 0.J. C h . Educ 1989,66,964. 13. Vestling, M. M.J. Chem.Edu. 1880,67,27P275. 14. Gtissom, C. B.: Grissom, J. WA1driehim;ecl Ada 1985,18,30. 15. Bell, W L.; Edmondson, R. 0. J. Chem Edue 1986,63,361. 16. Jacobson, B. M. J Chom E d u 1988.65.459. 17. Ruekberg, B. J Chrm Educ 1989.66.89, 18. Greenberg, F H. J . C b . Edue 1915.52.120, 19. SfoweU, J.C. J . C h . Educ 1819.56.422. 20. WinaM1.A. J. Chom Educ. 1980,67,162. 21. Yu. S. J. JChrm. Educ 1987, M , 312-613.
Synthesis of Metal Halides Karl Grube and Amos J. Leffler Vll anova -n vers ly Villanova. PA 19085
In the past few years both inorganic and organic undergraduate synthesis laboratory courses have switched from macro to micro or semimicro scale ~ r e ~ a r a t i o nMauv s. experiments have been developed and are described in new laboratow manuals (1.2). However. these do not amear . to include preparations for metal halihes that can be carried out on a gram scale. The following procedure allows synthesis of metal chlorides, bromides, oxychlorides, and oxybromides in good yields using up to a gram of starting metal or metal oxide. The basis of this method is the reaction of metals and halogens, primarily C1, or Ilrs, or the reaction of metal oxides and compounds such as carbon tetrachloride as reoresented by the equations below:
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Acknowledgment Chris Kinter acknowledees current s u ~ ~ ofrom r t NCI training grant ~ ~ - 0 9 1 9 9 . I ~ authors he &o wish to acknowledee their mentor. Garv H. Posner of the Johns HODkins ~ ~ i e r s i tin y ,whobe la6oratories the concept of t h k paper originated. Literature Cited 1. Zipp, A P J Chem. Educ. 1989.66.9566957. 2. Chloupek-McCough. M.J. Chem. Edue. 1998,66,92. 3. Mayo, D. W; Pike, R. M.; Butcher S. S. Micmsmlp Olgonlchb; Wile?: NewYork, 1
sas
4. Willismaon,K. L. Mkmsmk 0~gonkErp~~;wnLs:Heath: Lexington. 1989. 5. Mills. J. L.; Hampton, M. D. Mlcmsmk Lab Monud Far Opmml Chemistry: Random House: New York, 1986. 6. Kdb, K E.; Field, F W; Schatz, P. F. J Chm. Edur 1880,67,A304. 7. S0manathan.R. J. Chm.Educ 1953,60.526. 8. Lawler, R. G.: Parker, K. A. J. Chrm Edvc 1988.63.1012. 9. Hardin& K E.; Kinnel, R. B. Organic Pmpamlbnr and Pmndurea, InN. 1970.2, 313-31 4. 10. Landgrebe, J.A. J Chpm Edue 1898.65.460-461.
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Journal of Chemical Education
M(s)+ nXz MOzW + 2CC14(l) + MC14(I)
+ 2COC12(g)
Note that in the first reaction only the product is formed while in the second phosgene is a product and must be properly vented. CBr4is not particularly useful because of its low volatility. Apparatus The reactions are all run in the 500-900 'C range and require a vycor or quartz reactor tube. The dimensions of the reactor depend on the furnace used. In our work we used a 15 mm vycor tube with vycor to Pyrex graded seals placed so that both seals are out of the furnace. (See the figure.) The length of the hot zone was about 9 in. Modern versions ofthe furnace allow the furnace temperature to be set a t any desired value, but ours required a n external temperature controller and a thermocouple. Depending on the experimental set-up it may be necessary to wrap heating tape on the outlet side of the furnace to insure that the product reaches the receiver. The temperature of the heating tape should be near the boiling point of the product. Procedure
Reaction of Metal and Bromine
A weighed metal sample of 0.5-0.7 g is placed in the ceramic boat and pushed into the reactor so as to be in the hot zone of the furnace. The receiving flask with a stopper is weighed empty and then attached to the reactor. Anitrogen inlet tube is attached to the top of the addition funnel and the flow started to purge the air from the system. The heating tape is wrapped around the reactor as shown and (Continued on pageA206)
