the microscole laboratory Fluorocarbon Bubbler Fluids for Reactive Gases Alan 6. Brown,' J. W. Kosmeder, Paul D. Gaska, Chris W. Chronister, and Luis P. Barthel-Rosa Florida Institute of Technology Melbourne. FL 32901
Zinc Wool
Very efficient micro-Kipp gas generators can be fabricated easily from glass vials or test tubes that just fit into a 50-mL flask. The bottom of the vial is heated in a flame and a hole is punched into it with a metal file tip. A 112-in. loose plug of glass wool is placed in the bottom of the vial over the hole, after which the vial is filled with mossy zinc for hydrogen generation. A l-hole stopper, bent glass tubes, and a inchc cock are attached as shown in the firmre. About 30 m i of 6M HC1 is added to the 50-mL flask, and the generator tube is inserted. The entire apparatus is then placed in a 400-mL beaker to catch the displaced water when the rockets are filled. The rockets are filled with water and placed over the generator exit tube. On opening the pinchcock, the acid in the flask flows into the generator tube and contacts the zinc, producing hydrogen, which displaces water from the rocket. When the desired quantity of hydrogen has been introduced into the rocket, the pinchcock can be closed, which causes the reaction to cease as the residual gas forces the acid from the reaction tube. The zinc is slowly consumed in use and the acid solution must be replaced as needed. Oxygen generation and introduction into the rocket can be accomplished in a similar manner by placing solid manganese pieces in the generator tube. These usually have &iicie& oxide coating to catalytically decompose 3% hydroeen solution. The maneanese dioxide is not - ~eroxide . consumed, but the peroxide solution must be replaced as needed. Theoretically, 30 mL of 6M HCl should yield about 2 L of hydrogen gas, and 30 mL of 3% hydrogen peroxide should yield about 0.3 L of oxygen gas. These gas generators have been in use intermittently in the author's lab for several months now and are working perfectly. Other gases can be generated from insoluble compounds plus acid, such as carbon dioxide from calcium carbonate, hydrogen sulfide from iron pyrites, nitrogen dioxide from copper metal and concentrated nitric acid, and sulfur dioxide from an insoluble sulfite. The gas exit tube can be modified to meet the use.
In order to measure the rate of Clz delivery (at rates of -5 mumin to a 5 % accuracy) for semimicro-scalechlorinations, it is customary to use a bubbler calibrated by wunting bubbles for a measured volume of Nz. The use of paraffin oil in such a bubbler has been found to be unsuitable, however, because passage of Clz for 8-10 h renders the oil very dark and highly viscous, and bubbles grow visibly much larger. Since C12presumably destroys paraffin oil by reading with the olefins in it, other gases that react with alkenes. such as HCI and SO..-. are also of interest. While the efficts of HCI and SO2 are less spectacular than that ofCI?,overnight treatment of an oil buhbler with these plses dues lead to darkening of the oil, and calibration of the oil bubbler before and after such treatment with either gas gave volumes per bubble that were significantly different (table, entries 1and 2). In an effort to find a more inert bubbler fluid. the use of fluorocarbons, especially perfluorodecalln ~ P F Dwhich I is hest-known as a blood s ~ b s t i t u t ewas , ~ ex~lored.Indeed. the PFD in a representative bubbler remained colorles~ throughout a 72-h chlorination, and its viscosity and volume did not appear to change. Further, calibration of the bubbler before and after the chlorination gave volumes per bubble that were constant within experimental error (table, entry 3). Thus, PFD is a satisfactory bubbler fluid for measuring small amounts of Clz gas. Furthermore, calibration of a PFD bubbler before and after overnight treatment with SOz or HC1 gave volumes per bubble that were constant within error (table, entries 4 and 5), which indicates that PFD would be suitable for use with these gases as well. Since PFD is relatively expensive ($25.55125g),3the use of perfluoro-1,3-dimethylcyclohexane (PFDMCH; $58.301250 g)3 was investigated. Unfortunately, -50% of this material volatilized during an overnight chlorination. The other fluorocarbons we know of that are significantly 'To wnom corresponaences h o ~ d be addressea %ev~ew Ress, ,G . -e Blanc M Pure Appl Chem 1982, 54.
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3~ldrichChemical Co., Milwaukee.
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Journal of Chemical Education
Calibrations of a Sample Bubblera
Volume per Bubble (mL) Beforeb ~neP 1 oil SO2 0.17(1) 0.101(9) 2 oil HCI 0.18(2) 0.146(15) 3 PFD C12 0.14(1) 0.141(9) 4 PFD SO2 0.0812) 0.1011) ., , , 5 PFD HCI 0.1111) 0.12(1) a: Volumes were derived from 11-17 trials of 2 & 4 bubbles each, akr Entry
Fluid
Gas
:
.....
..~
-.....
less expensive than PFD (bp 142 "C) are also a t least a s volatile a s PFDMCH (bp 101-102 "C). I n sum, perfluorodecalin is a suitable bubbler fluid for measuring small flow rates of Clz, SOz, or HC1. We would expect it to be usable with other gases of similar reactivity toward alkenes; Clz, HC1, and SOz react with alkenes by three different mechanism^,^ and thus represent three distinct classes of gases for which PFD bubblers will be useful. Acknowledgment We thank J.C. Baum of this department for loans of h hardwareandC.H. Vanselow I ~ n i v e r s iot f~~ o r t Carolina a t Greensboro~for helpful discussions. This work was supported by the ~ l o r i d aInstitute of Technology ~ e s e a & h OEce. and bv the donors of The Petroleum Research Fund, admidistered by the American Chemical Society.
Synthesis of trans-2-tert-Butylcyclohexanol via Hvdroboration: A Microscale Oraanic Exoeriment Demonstrating Syn idi it ion ' Carl T. wigal,' William T. Hopkins, and Bruce P. Ronald Idaho State University Pocatello, ID 83209 The hvdmboration reaction. first reported bv H.C. Brown in i956 (I), is a classic example i f regio&emical and stereochemical control. The addition of borane to a n alkene produces an organoborane that upon oxidation with basic hvdroeen oeroxide results in svn addition of water in an a n t i - ~ a r k o v n i k o v fashion: While t h i s reaction demonstrates imvortant mechanistic aspects of alkene hydration, the stereochemical consequen&s have been difficult, ifnot impossible, to prove in a typical organic teaching laboratory. Previously reported hydroboration experiments (2-5)have failed to address these mechanistic issues or
required the preparation of derivatives to determine the relative stereochemistry of the addition. We have developed a microscale experiment, the hydroboration of l-tertbutylcyclohexene, which d e m o n s t r a t e s both t h e reniochemical a n d stereochemical outcome of t h e hy&oboration reaction via a melting point and a Jones oxidation test. This reaction is auite simple in both procedure and equipment needed yet demonstrates uneqtuvocally themechanist~caspcctsofthehydrohoration reaction. Experimental All reagents used in this experiment are available from Aldrich Chemical Company Inc. and were used without further purification. 4C12and HCl: Streitwieser, A,, Jr.; Heathcock, C.H. Introduction to OrganicChemistry,3rd ed.; Macmillan:New York, 1985;pp 255-262. SO,: Rogid. M.M; Masiiamani, D. J. Am. Chem. Soc. 1977, 99, 5219-5220.
I n a 10-mL round bottom flaskz equipped with a CaClz dryingtube, magnetic spin vain, and aircondenser is added 1-tert-butvlcvclohexene (0.366 mL. 2 mmoli. Added slowlv to the flack \;ia syringe is 1.0 M B H ~ T H F( 2 0 mL, 2 mmolj. After addition of the BH.-THF. the reaction mixture is allowed tn stirat room trm;eraturefor 1 h Added dropwise to the rpactlon mixture wh~lestirnneis 3M NaOH 110 m1.1 followed by 30% hydrogen peroxide'il.O mL). Caution: 30% KOzcan cause blistering of the skin! While being stirred, the mixture is heated for 45 min a t reflux using a hot water bath and then is transferred to a glass centrifuge tube allowing the mixture to cool to mom temperature. The reaction mixture is extracted with dichloromethane (3 x 1.0 mL). The combined organic phase is washed once with water (1.0 mL), dried over anhydrous NazSOa for 10 min, and transferred to a tarred vial for solvent removal under a stream of' nitrogen. The white crystalline pn~ductis we~ghedand the melting point detrrmined. Asmall sample is used fur a Jonenox~dationtest 31. Discussion We have found this exveriment to be a valuable addition to our laboratory curricuium. Atypical student yield of this reaction is -75 % with exclusive formation of the trans isomer a s determined by gas c h r o m a t o g ~ a p h ~ T .h~e regiochemistry of the addition is determined by the Jones oxidation test. The Jones oxidation test, in this case, differentiates a secondary alcohol (anti-Markovnikov addition) *om a tertiary alcohol (Markovnikov addition). Therefore, 2-tert-butylcyclohexanolsgive a positive Jones test while 1-tert-hutylcyclohexanolgives a negative Jones test. The stereochemistry is determined by the melting point. The trans isomer has a meltina point of 84-85 "C (6)while the cis isomer melts at 66-57 ' F ( 7 , .A typical melting range of thenudealn,holforstudents was76-81 'C . Subhnination of the crude alcohol can be carried out in a beaker or test tube by heatinp the material on a 80 "C sand bath for 5-10 min rcsultinl: k formation of long needle-like crystals on the walls of the container. Melting- range of the sublimined crystals was 82-84 "C. Acknowledgment We would like to acknowledge the participation of the students of CHM 304 a t Idaho State University for their assistance in developing this experiment. Literature Cited . . . . 3. Mayo, D. W.:Pike,R.M.; ~uteher,S.S. ~ i m s m O~ganie k Lobomion; Wllw: New York,1989. 4. Goach, E. E. J. Chm. Edur. 1990,67, A232. 6. Picketing,M. J Cham.Educ. 1990.67, 436. 6 Milstein, 6I3A 126. 7. Beilsleix, 6131, 125.
'Author to whom correspondence should be addressed. 2Thissynthesiscan also be carried out on a 112 scale to accommodate a 5-mL conical vial. =GCanaivsis 110%Carbowax. 2 m x 1/8". 120 OC. He 50 mL/min.\ of the comherial mixture of isomers gave the following retentioi times: cis isomer, 9.02 min.: trans isomer, 9.98 min. Volume 68 Number 12 December 1991
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