A Versatile System for Vacuum-Line Manipulations Andrea L. Wayda and James L. Dye1 AT&T Bell Laboratories, Murray Hill, NJ 07974
Vacuum-line manipulations are commouplace in the research laboratory and are usually an integral part of undergraduate laboratory courses in physical and advanced inorganic chemistry. The general techniques have been well documented (1). both for hiah-vacuum methods and for the handling of air-sensitive compounds (21. One of the authors (JLDI has followed the develo~mentof these techniques from the exclusive use of greased ~ t ~ ~ c oand c kjoints s to the present extensive use of Teflon valves and O-ring connectors. Persistent problems, common to hut not confined to, the undergraduate laboratory, include contamination of the vacuum line &d pump, the need to regrease stopcocks and take-offs after exposure to solvents to prevent leaks and, most disturbing of all, glass breakage caused by the need to make rigid connections to the vacuum manifold. The synthesis of air-sensitive compounds and the transfer of toxic liquids from steel cylinders into glass vessels also present prohlems which are usually solved by using Schlenk lines andlor syringe technique (3)in a fume hood. Faced with the need to carry out svntheses with alkali metals dissolved in ammonia, amines and ethers ( 4 4 ) , we have designed a dual manifold and ueriuheral eauiument that permit easy handling and transferbf &es, liqiids, and pre-
cipitates within a completely closed system. By making use of stainless steel flexible tubing, the apparatus need not be connected rigidly to the manifold. This reduces the set-up time and eliminates the major cause of glassware breakage. Such a system should be generally very useful both in research and in the teaching laboratory. The Vacuum System
The heart of the vacuum system2is the glass dual manifold shown in Figure 1. Except for an extremely light coating of silicone vacuum grease on the valve backing O-rings, the system is greaseless. In operation, the top manifold is always maintained under diffusion pump vacuum with the manifold
' On sabbatical leave from Michigan State University, East Lansing,
MI 48824. Most of !he items described in this article are available from variws
manufacturers and suppliers. To assist the reader in obtaining an accurate description and cost estimate of the system, we have indicated the supplier of the parts we used (where applicable).Prices quoted are approximate 1983 cost figures.
Figure 1. Waking layout of greaseless double-manifoldvacuum line. Note in panicular A) NHa/volatile solvent inlet system and 6) assembly for predrying ammonia. 356
Journal of Chemical Education
pressure indicated by a Penning gauge3 or ionization gauge.4 The bottom manifold can be opened to a source of solvent, to the synthesis vessel, to the top manifold, or to a roughing pump equipped with a thermocouple gauge.5 Solvent vapors and gases are transferred through the bottom manifold after i t and all connected pieces of apparatus have been thoroughly evacuated and out-gassed. Residual solvent vapors can he condensed into the synthesis vessel or into an auxiliary flask by cooling with liquid nitrogen. Once the vapors have been condensed. the lower manifold can be oumned out with the roughing pump and then opened to the upper high-vacuum manifold. In this wav. amounts of solvent vaoors .. anoreciable -. are prevented from release into the room or through thebacUUm DUmD. Thk vahes on both manifolds are 90° 8-mm Teflon valves with O-ringseats."Since the upper manifold isnever exposed to solvent Gapors, Viton O-rink can be used without d-anger of solvent degradation. Similarly, the backing O-rings on all valves are protected from solvent vapors by Teflon wipers so that the choice of elastomer material for these O-rings is not critical. Howrvrr, the seat O-rings and those on thei>intsof the lower manifold must becompatible with the solvents wed. In general, Viton O-rings can he used for nonpolar and chlorinated hydrocarbons and ethylene-propylene copolymer O-rings for polar solvents. Kalrez O-rings,7 although very expensive, can be used with either type of solvent and are very useful for solvents such as THF. The main stopcock on the cap of the top manifold is a 12-mm Teflon valve6 that ooens the manifold to a liauid nitrogen trap. This trap is connected to the diffusion p i m p via another 12-mm valve and a length of l-in.-diameter flexible stainless steel tubin9 equipped with Ultra-Torr fittings? This tubing must be rigidly clamped to avoid undue force on the trap when evacuated. A diffusion pump hy-pass is provided by a length of 3/~-in.flexible stainless steel tubina.8 The other end cap; on themanifolds are 20-mm O-ringjoints mated to 20-mm O-ring adapters equipped with 90° 4-mm Teflon valves6 and 3/s-in.ro.d. glass tubing for easy connection of Ultra-Torr fittings. A convenient feature of the manifold is the ease with which it can he dismantled for cleanine. The system is designed for use with either 15-mG0-ring ioint-eauinned . .. "elassware or with Ultra-Torr fittines. The vacuum gauges are attached via the intermediacy of tGe latter and can be readily removed if necessary. A spare port is provided on the top manifold for comparing two vacuum gauges
if desired. Take-offs consist of 15-mm-O-ringjoints that can be used directly with compatible glassware or can he equipped with 15-mm-O-ring to 3/8-in.-o.d. adapters for attachment of flexible tubing. The modular nature of the system allows complicated glassware (such as that used in multiple trap-to-trap transfen) to he assembled, pumped down, and used, and then disassembled and cleaned with relative ease and speed. Effectively, the simple double manifold functions as the access port to high vacuum and as the template for the assembly of virtually any high vacuum set-up with economy of space and simplicity of design. Auxiliary Apparatus Synthesis vessels, such as the H-cell shown in Fieure 2 (easily fabricated hy modifying a Kontes "~irless-ware"Hcelllo) are attached to the manifold with flexible stainless steel tubing. This makes i t easy to clamp the cells a t a convenient location, to shake them to mix the contents, to pour liauids from one arm to the other, or to immerse them in a'controlled-temperature bath. The introduction of volatile solvents such as ammonia, methylamine, dimethyl ether, etc., which are usually purchased in steel cylinders, is also accomplished by using flexible tubing. If standard Y-in. or 3/s-in. 0.d. tubing can he attached t o the cylinder, the connection via Ultra-Torr fittings is straightforward. For tanks that are equipped with a hose nipple, we have successfully attached 3/~-in.0.d. glass tubing by using heat-shrinkable Teflon tubing (or Tygon tubing with a %-in. copper tube insert).ll I t is essential to monitor the pressure in the connecting tubes and the lower manifold during vapor transfer. This can be readily accomplished by attaching a small vacuum-pressure gauge1=to an Ultra-Torr tee which can then be inserted in the delivery line. Figure 1 gives the details of a typical set-up for use with two tanks. Solvent Purlflcatlon All of the solvents that we used (except ammonia) were purified prior to anaerobic use; for example, T H F was stirred over calcium hydride followed by distillation into a flask which contained benzophenone and a slight excess of sodium-poGPK326C Vacuum Penning Gauge with Sensor (Part #280460), $910 complete. CVC Products, P.O. Box 1896, Rochester. NY 14603. Analog ionizat!on gauge. Televac 3C5-IR, $750 without tube, $820 with tube. K l p t J. Lesker Co., 5635 Hwning Road, Pittsburgh, PA 15236. Digital ionization gauge. VEECO RG1000, $1235 complete. VEECO. Terminal Drive. Plainview. LI, New York 11803. Varian Model 801 Thermocouple Gauge, $180 complete. Varian Associates. 331 Montvale Avenue, Woburn, MA 01801. B K ~ n tK-826510: e~ 0-4 mm, $28.10.0-8 mm. $44.90.0-12 mm 552.30. Kontes, Spruce Street, P.O. Box 729, Vineland, NJ 08360. Kalrez O-rings (availablethrough Kontes).Size 01 I, $24.50. Size 116. $38.10. Cajon Stainless Steel Flexible Tubing (availablethrough R. S. Crum & Co., 1181 Globe Avenue, Mountainside, NJ 07092). 3/8-in. o.d., 6-in., flexible length, 321-6-X-6, $25.10. 3/8-in. o.d., 12-in. flexible length, 321-6X-12, $35.60. 3/8-in. o.d., 24-in. flexible length, 321-6-X-24, $52.20. Sleeve inserts for %in. 0.d. 304-6XOA, $2.50 each. l-in. o.d., 12-in. flexible length tubing. 321-16-X-12. $80.40. Sleeve inserts for l-in. o.d., 304-16-XOA, $4.00 each. Cajon Uitra-Torr unions and tees (alsoavailable through R.S. Crum a Co.) 3/B-in.brass union. 56-VT-6, $8.00. =Irin. stainless steel union, SS6-UT-6, $17.20. l-in. brass union, B16UT-6, $23.20. 3/rin. X '/4-in. MPT Connector, stainless steel. SS-6-UT-1-4. $11.60. 3/8-in. 0.d. stainless steel tee, SS-6-UT-3, $32.50. 'O Kontes Double Tube "H" Cell, K-218550, $110.00. " Variousdiameter heat-shrinkable Teflon tubing is available from Pope ScientificCo., P.O. Box 495, Menomonee Falls, WI 53051. l2 Matheson pressure-vacuum gauge. 63-2204 (30 psi). $54.50. Matheson, P.O. Box 85, 932 Paterson Plank Road, E. Rutherford, NJ 07073.
'
Figure 2. Ktube reaction cell
Volume 62
Number 4
Aoril 1985.
357
tassium alloy. The latter procedure yields a purple solution of the benziphenone ketil and dianion thai reacts rapidly with water and reducible impurities and serves as an indicator of dryness. The drying flasks were attached to the bottom ~ manifold via flexible tubing and an intervening t r a cooled with liquid nitrogen. In this way it was possible to handle solvents as volatile as dimethyl ether (h.p. = -24'C) by cooling the flask to -20°C (or below) or as involatile as ethylenediamine (h.p. 22OoC) by heating under reflux. However, solvents of low volatility should not he distilled through the bottom manifold because they will contaminate i t and pump out onlv verv slowlv. Rather. distillation bv vacuum transfer is conducted throigh an external tee, separated from the manifold hy a liquid-nitrogen-cooled trap. After purification, volatile solvents such as dimethyl ether, methylamine, and trimethvlamine were distilled throueh the bottom manifold into 5 0 d m stainless ~ steel tanks.13 " Procedures
Ultra-Torr fittiness and flexible stainless steel tubin@ permit easy and ver;atile connection of glass apparatus to tKe manifold. Manifold pressures of 10-4torr are easily obtained and careful outgassing permits one t o reach pressures below 10-5 torr. As discussed in the previous section, trap-to-trap distillations through the bottom manifold can he easily made with volatile solvents while less volatile solvents can he distilled externally through a tee. In addition, there are no constraints imposed by the need to clamp the apparatus carefully i n a partict~larlocation when it isattnched toihe vacuum line. This feature substantially reduces the time and effort required t o set up simple vacuum distillations, sublimations, etc. Involved vacuum manipulations are conducted using connector-compatible glassware assembled in a "building-block" fashion. The most commonly used accessories, connectors, etc.. are shown in Fieure 3. The synthesis andhandling of air-sensitive materials can often be faciliutted bv a combination ofrlove-box urocedures and the vacuum line techniques described here. he reaction flask mav he loaded with air-sensitive reazents in a dove-box before being attached to the vacuum line. After evacuation, the solvent is distilled into the synthesis apparatus and the rractanrs are mixed. The use of an H-cell permits reacrants to be mixed, prwides for the handling and filtration of precipitates, and allows insoluble materias to be washed b; repeated distillation of solvent from one a n n of the H-cell to the other followed by filtration through the frit. If the products are air-sensitive, they may he removed from the H-cell in a svdove-box. Our exnerience with Schlenk-line svntheses. ~~~~, k g e techniques, and reactions carried out in a glove box has convinced us that the vacuum-line methods described in this
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~. ~~
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article are useful complementary procedures t o the more established techniques for handling air-sensitive materials. A Specific Example
Our use of metal-ammonia solutions as reducing agents (4,
5) demonstrates the usefulness of the vacuum system and H-cells in a demanding application. Matheson Electronic Grade Ammonia from a size 3P cylinder equipped with a stainless steel regulator" (capable of delivery a t less than atmospheric pressure) was used directly. The ammonia was predried in a 100-mL round-bottomed flask that contained a mirror of sodium or potassium metal. The metals were introduced into the flask by quickly hreaking a small-diameter glass tube that contained the alkali metal (7). Evacuation, followed by heating, produced a mirror of the metal. The flask was separated from the manifold by afrit contained in a short section of tubing with a 15-mm O-ringjoint15 on each end (Fig. 1). The H-cells were loaded in an argon-filled glove-boxl6with the compound to he reduced in one arm of the cell and the metal in the other arm. Alkali metals were contained in small-diameter tubes so that a measured length could he dropped into the H-cell, thus providing a known amount of metal. Europium and ytterbium were introduced as the powered metals. After removal from the glove-box, the closed H-cell was attached to the lower manifold with a 2-ft. length of flexible stainless steel tubing. By using the lower manifold and the roughing pump, all ronnecting tuhes up to the H-rell and the ammonia tank were evacuawd; then the H-cell was evacuated. The entire system, including the previously evacuated predrying flask, was then opened to the upper high-vacuum manifold and evacuated to to l O W torr. The H-cell was left open to the upper manifold and evacuated while ammonia was distilled from the tank into the dwinn flask. This illustrates the..f.oreground-background"ca~hiIitiesof the system. HY cooling this flask with a dry ice-isopropanol bath. a d e e ~ blue metal-ammonia solution was formed which sewed t o remove reducible impurities. The frit was out-gassed by heating with a torch, and the l3 MatheSOn 500mL capacity stainless steel stwage tanks, 4HS500. $104.00. Matina valves for Drecedina. MM4374. $82.00. l4 Mameson ilecbonic &ade ~ m i o n i acylinder , sire 3P (2.27 kg). $102 T deposit. Stainless steel regulator (capabe of delivery below atmospher~cpressure). 3501-660. S280.00. ' 5 O-ring joints available from Ace Glass, Inc., P.O. Box 688, 1430 Northwest Boulevard, Vineland, NJ 08360. Cat. No. 7646, 15 mm, $4.50. 20 mm. $5.00. Securing Pinch Clamps, Part No. 7650. Size 28. $6.30. Size 25. $7.40. '"Vacuum Atmospheres HE-43 Dri-Lab with recirculated argon atmosphere.
Figure 3. Commonly used accessories and connectws: A) Cajon Ultra-Ton Union, 6) Caion Ultra-Tarr Tee, C) Cajon flexible stainless steel tubing (@ Markad Service Ca./all rights reserved). 358
Journal of Charnirnl Frl~lratinn
1977-1983
bottom of the metal-containing arm of the H-cell was heated under a vacuum to form a mirror of the alkali metal on the side wall (!anthanoid metals were gently warmed to out-gas them). The metal-ammonia solution in the solvent purification flask was frozen with liquid nitrogen, evacuated to high vacuum, and then permitted to melt and distill into the H-cell. The fritted disk between the drying vessel and the manifold prevented "spray carry-over" of metal during the distillation. When sufficient ammonia had been distilled into the H-cell, the cell was removed from the vacuum line and placed in a cooling bath. By predrying enough ammonia and using two connectors, two or three H-crlls could be handled in a single operation. Useful lightweight containers for the cold bath (isopropanol cooled by dry icejwere made from discarded expandedpolystyrene acid cartons lined with polyethylene. Half of such a carton has two chambers which can contain cooline baths at different temperatures to facilitate distillation of so&ent from onearm of the H-cell to the other. The middle oortion of the H-cell rests in a shallow groove cut between the two chambers. After cooling the H-cell, the metal-ammonia solution was poured through the frit into the compartment which contained the compound to be reduced. (Alternately, if the com~oundis soluble in ammonia, that solution can be poured through the frit into the mctal solution). N'hm ihe reduction was complete, the ammonia was distilled from the H-cell hack into thedrying vessel which was cooled with liquid nitrogen. This flask was then removed from the vacuum line and placrd in a fume hood until the ammonia had evaporated. Frequently, the reduction product was insoluble in ammonia. It could then he re~eatedlvwashed with ammonia hv distillation and filtration. since ail of our reduction products were air-sensitive.. thev.were removed from the H-cell in an argon-filled glove-box. In addition to their use for metalammonia reductions. we have used H-cells successfullv to prepare salts of alkali metal anions by using the solvents methylamine, dimethyl ether, and trimethylamine. Safety Precautions Although we have minimized the risk of implosions by using flasks no larger than 1L, elass vacuum svstems should always be treated as if an impl'o&n were imminent. Safety glass& or goggles are always required and face shields and/or equipment shields should be used when large flasks (>300 mL) are evacuated. Particular care must be used when traps are cooled with liquid nitrogen. Air must not be permitted to enter the system sincr condensation of appreciable amounts of uir followed by warm-up will inevitably cause u closed glass system to explode. Such a catastrophic event can happen lo a system under dynamic vacuum, when traps become clogged with solvent converting an open system into a closed one. The use of pressure gauges on the system during transfer from steel cylinders greatly reduces the risk of explosion but care must be taken to monitor the pressure constantly and keep it at or below atmospheric pressure. The system described in this paper provides a measure of protection against glass breakage by overpressure since the Ultra-Torr fittings will generally blow off a t pressures below those which would burst smalldiameter glassware. In addition, the O-rings in the joints will blow out under pressure. These built-in "safeguards" cannot be relied upon: however, and prudence requires that the pressure inside of the manifold and attachments be kept at or below atmospheric pressure. Since we used such toxic volatile solvents as ammonia, methylamine and dimethyl ether, the vacuum lines were installed inside a fume hood, addition, the vacuum pumps were also vented into the hood. 17 ~h~ glass dual manifold (including vacuum trap) is available from Crown Glass Co.. 990 Evergreen Drive, Somewiile, NJ
08876.
Cost Comparisons We have constructed two vacuum svstems of the tvoe described in this article a t AT&T Bell ~gboratoriesanci bne a t Michigan State University. The individual retail prices of the valves and joints used to construct the manifold shown in Figure 1are given in the footnotes. The total retail materials cost per manifold (with trap) was $650. This figure compares with a materials cost of $822 for a similar manifold constructed with 6-mm bore high-vacuum greased stopcocks on the take-offs, 10-mm bore stopcocks on one end and the trap, 4-mrn bore ~tnpcockson thk other ends. 29/12 standard taper jointson the manifold ends,and a 14135standardtaper ioint on each take-off outlet. However, a conventional single manifold with greased stopcocks and joints would cost only about $465 for materials. The construction time ner manifold by a Master Glassblower is approximately 6 h. The complete manifold is now commercially available.11 The cost of the flexible stainless steel tubing and Ultra-Tom fittings depends upon the intended use. A minimal set would consist of connections to the diffusion pump and vacuum gauges ($181), two 24-in., two 12-in., and one 6-in. length of flexible tubing, two stainless steel and four brass unions and one stainless steel tee ($338total). Thus, a complete manifold and accessories, exclusive of pumps and vacuum gauges would cost approximatelv $1120. If two steel storage cylinders are requirid, their cost, together with that of'the associated gauges, tubing, and fittings is $720. The diffusion pump and two mechanical pumps add $3000, while the Penning and thermocouple gauges add $1200 to the cost. Therefore, a complete system such as that descrihed in this article would cost roughly Sti5OO:l'o put the custs in perspective, it should be noted that the added expense of the flexihle tuhing and fittings required to versatile system is only asmall percentage of the total system cost. Summary and Conclusions The vacuum system described in this paper is versatile and easy to use. Because of its modular construction and virtually greaseless stopcocks and joints, it is easy to clean and to keep clean. Perhaps its most valuable feature is the fast and worrv-free wav in which auiliarv. apparatus can be connected .. to t i e line without critical alignment and clamping. The "foreground-backaound" use of the two manifolds saves time and the fact that one of them is always kept under high vacuum substantiallv reduces pump-out times. In the teaching laboratoiy, the ability to connect and remove apparatus quickly from the l i e and the ease with which this can be done without breaking either the apparatus or the vacuum line should he valuable features, especially when a number of students must share a single vacuum line. In the synthesis laboratory, whether the research is done by undergraduates, graduate students, or post-graduates, the ability to exclude air rigorously, introduce solvents of various volatilities. and carrv out the usual manioulations of ~reci~itation. . . filtration, and distillation make suih a system very useful. ' Acknowledgment We wish to thank D. W. Murphy and S. M. Zahurak for their helpful sueeestions and observations durine the evolution of this vac&m system design. We also thank'].'. 5. Hates for initially brinrinr - - the versatilitv of Caion connectors toour attention. Literature Clted (1) L S P ~ I IR. ~ R.. , -practicalvacuum systems? M~G~~W-H N~~ ~ I Iyorkk, . IWZ. (2' Shrive'. D. S.. "The Manipulation of Air Sensitive Compounds? MeGrsu-Hill, New York, 1969. (3) B-. H.c..(toehniques by K ~ ~ ~w.. ~ L~~ W, , A GB. .. , w ~idl land. M.~.)."~lgani~ SynthesnViaBoranes."John Wiley and Sons, New Yark. 1975. (4) Ww3a.A. L.. Dye, J. L..and R o w s . R. D., Or#onom=fallics, 3,1605 11984). ( 5 ) Murphy, D. W., Dye, J. L., and Zahurak, S. M.,lnorg. Chem., 22,3619 (1983). (6) Van Eck, B., Le, L. D..lsss, D.,and ow, J. L. IW. Chem., 21,1966 (19821. (1)Dye, J. L., J Phvs. Chrm..84,10&I (1980).
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