Simple and Versatile Vacuum and Pressure Reactors for Air-Sensitive Materials Neil Burford, Jurgen Muller and Trenton M. Parks Dalhousie University, Halifax, Nova Scotia, Canada B3H 4J3 With the availability of high quality inert atmosphere apparatus (dry boxes), efficient vacuum pumps and elaborate vacuum svstems. as well as established techniaues for performing almost any experimental manipulation under an atmosphere of dry nitrogen (Schlcnk techniques), the handling ol'air-sensitive compounds poses little problem to the modern synthetic chemist. However, many of the procedures required to maintain pristine atmospheres involve either intricate maneuvers with sophisticated apparatuses or are incomplete in terms of rigorous exclusion of moisture or other impurities, such a s grease. Moreover, the available techniques tend to develov characteristics of the experimentalist performing the operations and may have deficienc~esthat are not readily apparent or art: difficult to reproduce. As a consequence, it i6 rare to find an undermaduate teachine laboratow that involves the hundline - of critically air-sensitive materials, despite the predominance of such substances in the current literature. Our work with highly electrophilic nonmetal cations ( I ) has necessitated the develo~mentof s i m ~ l eversatile. . robust and atmospherically reliible apparat;s, that we f e k ~offer substantial benefits over other, previously reported systems. Here we describe the reactors and the procedures that allow us to perform synthetic chemistry and analysis under anhydrous and anaerobic conditions with relative ease, and with reproducibility and simplicity appropriate for a n undermaduate laboratow. l he heart of our apparatus is based on the revolutionary vacuum H-tube reactor described bv Wavda and Dye in 1985 (2).Our reactor, that we refer to a s abridge, is vacuum-tight vessel that has two or more separate compartments. The entire bridge is connected directly to the vacuum line bv means of a standard mound elass "ioint that is associatedUwiththe main stopco&. Alternatively, the vessel mav be modified readilv to enable connection to a vacuum line through the use of flexible stainless steel tubing (21. . . The oracticalitv and versatilitv of the svstem is conferred through the-use of demountable anduinterchangeable reaction chambers or compartments. The reactors are constructed from borosilicate glass components that are connected through the use of Nylon or Teflon bushings seated in threaded glass connectors. Avacuum-tight seal is formed by a FETFE (or other appropriate material) O-ring between the bushing and a glass flange of the connector. Teflon stopcocks are used to isolate the compartments.'A
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'AII components are available from Ace Glass Incorporated, P.O. Box 688, Vineland, NJ 08360. Bushings are available in either Teflon or Nylon and with inside diameters ranging from 7.5 to 76.5 mm (Ace Code 5029 or 7506).Ace-Thred threaded glass connectors are avaiiable in sizes corresponding to the bushings (Ace Code 5027 or 7644). O-rings are available in a variety of materials including viton, silicone, buna-N. FETFE, ethylene-propylene.CAPFE. Kalrez 4079, and Chemraz 515, and in sizes ranging from an I.D. of 2.9 to 110.5 mm (Ace Code 78551. Stoococks are available in a number of stvles. We prefer to Jse baieaolb n gn vacdm stopcocks w t n easy a&#on p ~ g and s ether the domle Teflon r ng or tnree FETFE 0 - r ng seals ,Ace Code 8192.8193 an0 8194) These are ava la0 e nor Ices zes from G 3 to G I 5 mm and include the borosilicate glass barrels.
Figure 1. Photograph of a typical tdple-compartment bridge, fined with two 100-mL reaction bulbs and a 5-mm NMR sample tube. The threaded glass connectors are 15 mm diameter, the Teflon bushings are 14 mm I D , and the Teflon stopcocks fitted with FETFE O-rings are 0-5 mm aperture. view of a typical triple-compartment bridge, fitted with two 100-mL reaction bulbs and a 5-mm NMR sample tube is shown in Figure 1. A diagrammatic representation of a dual compartment bridge is shown in Figure 2, and a n expanded view of the O-ring seal is illustrated in Figure 3a. These seals typically maintain a vacuum as high a s 10-3 torr for a period of two weeks or more, and withstand pressures up to a t least two atmospheres, such as are encountered in warmine dichloromethane solutions in hot water (-60 "C).In addition, we have developed a seal suitable for room temperature use with low-boiling solvents such as sulfur dioxide and ammonia (Fig. 3b) involving pressures a s high a s 1 3 atmospheres (3).Asecond smaller O-ring sits in a slight indentation in the elass tube and is locked onto the flange within the bushine. This vrevents release of the compartment from the connector. AS-withany vessel under Dressure there are certain cautionarv nrocedures that should be followed in case of explosion (knowledge of vapor
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Number 9 September 1994
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Compartment Neck
F ~ g ~3r eC~tawayvews of (a)a rqpcal 15 mm 0-nng seal on a 14mm glass IJomg companment new ana 10)a typcal 11-mm 0-r~ng seal, tnat nas oeen aoapteo forhlgn pressLre work, on a 10-rnmg ass tubing compartment neck.
Figure 2. A diagrammatic representation (to scale) of the parts of a typical dual compartment bridge. pressures a t room temperature and careful shielding of the anoaratus). range of sizes for the demountable reaction The compartments is 5 to 500 mL, and the bushings are available in sizes from 7.5 to 76.5 mm inside diameter. As illustrated in Fieure 1. the comoartments mav be reaction chambers orubulbs,' NMR tuies, W M S , solution IR, or electrochemical cells. Additional tvnes of attachments also may be constructed for more specialized needs. A typical reactor for a 1mmol scale reaction is constructed from 22mm diameter glass tubing fitted with 0-5 m m aperture stoococks and 15 mm threaded .class connectors (0.D. of thread is 26 mm,. An assembled triple a~mparltnentvessel !as oictured in Fin. 11 measures aooroximatelv 28x 10 x 30 &n 728 x 10 x 46 c k with NMR tube fittedj and weighs approximately 500 g. Such a vessel may be constructed by a master glassblower in approximately 12 h.
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Procedures While under dynamic vacuum the empty reactor is flame dried with a Bunsen burner for approximately 10 min, and then allowed to slowly cool to room temperature. I t is possible to heat the glass sections of these vessels close to the
2Gentler heating should be used near the stopcocks and joints since FETFE melts at 240 "C. 3Vacuum/Atmos~heresComoanv. , .. 4652 W. Rosecrans Ave.. Hawthorne, CA90250. 'MBraun GmbH, Gutenbergstafle 3, D-8046 Garching, Germany.
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Journal of Chemical Education
melting point of borosilicate without obvious detriment to the Teflon or FETFE c o m p ~ n e n t showever, ;~ Nylon bushings or stopcock heads may ignite if heated directly. All reagents and solvents used in the reactor are purified prior to use, employing conventional techniques such a s recrvstallization, vacuum, or inert atmosphere distillation or vacuum sublimation. Solid reagents are exposed to dynamic vacuum for a minimum of 30 min, and liquids are degassed using standard freeze-pump-thaw procLdures. The evacuated reactor and solid reagents are taken into a n inert atmomhere (Nv or Ar) drv box !Vacuum\Atmospheres3 or ~ r a & . ~ e a g e n t are s weighed and introduced into separate demounted compartments, and the reactor is reassembled, removed from the drybox, and re-evacuated. . Volatile reagents and solvents a r e vacuum distilled through a short bridge into the aoorooriate comoartment of the'reactor while The other cokpa&ments are isolated bv the stoococks. Combination of reagents can be nerformed in a variety of fashions including slow (dropwise) addition, the rate of which is controlled by the separating stopcocks, and reaction mixtures may be warmed or cooled readily. Additionally, the reactor has no orientational restrictions, and it is not necessary that it be clamped into position. A bridge may be constructed with a sintered glass frit separating n:action compartments, or a small adaptor containing a frit may be attached between one of the threaded glass pons and a companment. This allows filtration of' solid materials from solution, although w e have found that most systems may be separated by simple decantation of solutim from the solid. The separated solid may be washed bv repeated "cold spot" back distillation of solvent using a liquid nitrogen-cooied cotton ball. Precipitation of materials may be enhanced by concentration techniques that involve slow removal of solvent from the solution by cooling one of the other compartments of the reactor. either with liouid nitrocen for fast concentration (minutes) or with cold water for slow concentration (hours or days). Use of these techniques has resulted in crystal growth where other approaches have been unsuccessful. The resulting solids are then washed by repeated "cold spot" back distillations, a s described above. ~
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Isolation is completed by removal of the solvent from the reactor in vacuo, and then recovery of the materials in a drybox. Alternatively,because the stopcocks between compartments allow for the in situ preparation and purification of a reagent, compartments may be exchanged in order to introduce other reagents without compromising the quality of the reactor environment and without necessarily requiring a manipulation in the dry box. Such an approach is commonly employed in order to obtain solution NMR samples of a reaction mixture. After decanting an appropriately sized aliquot of the reaction mixture into an attached NMR tube, the solvent of the NMR sample may be exchanged for a suitable deuterated solvent and the frozen sample flame sealed. Future Developments The system described above is robust, extremely versatile, and easy to clean and use, but perhaps the most important feature is the ready interchangeability of the com-
ponents and the possibility of expanding the number and type of compartments almost indefinitely. The form and function of this system has undergone continual evolution through its use in our laboratory over a six-year period, especially with the contributions of Bruce Royan, Rupert Spence, and Mel Schriver, and we anticipate extensive developments in the future. Literature Cited .See, for example, Burford, N.: Loaier, P: Bakshi, P.K: Cameron, T S. J. Chem. Sac., Dalton Tram 1893,201-202; Burford, N.;Parks, T. M.; Royan, B. W.:Boreeka. 8.: Camemn. T. 5.: Richardson, J. F: Gabe, E. J.: Hyner, R. J Am. Chem Soc. 1992,
114,81473153:Burford,N.:Mason,S.;Spenee,R.E.v.H.;Whalen,J.M.;Richardson,J.F.; Rogers, R. D. Orgonometollicr 1992,11,2241-2250: Burford. N.: Parks, TM;Royan,B. W.;Richardson, J.F:White,PS.Can. J Chem. 1992,70,703-709; Burford, N.; Spenee, R. E,v. H.;Richardson, J. F J. Chzm Soc.. Dalton Trans. 189L 1615-1619; Burford, N.; Spence, R. E. v. H.; Rogers. R. D. J. Chem Sae., DaltonTrane. 1980,36113619: Burford, N.; Dipehand, A. I.: Royan, B. W.; White, P. S. Inorg Chem. 1990.29.4938-4944. 2. Wayda,A. L.:Dye, J.L. J Cbm.Edue. 1985,62,356359. 3. Wasylishen, R. E.; Burford, N. J Cham. Soc., Chem. Commun. 1987, 141P1415: Wssylishen,R. E.; Burf0rd.N. Can. J Chem. 1987,65,2707-2712.
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