Gary W. Kramer Purdue University Lafayette, lndiano 47907
A Convenient Method for Handling Small Amounts of Gaseous Reagents
With the advent of chromatographic separations and instrumental methods of analysis, the laboratory scale of many organic reactions has been markedly reduced. Today a five to ten millimole reaction scale is common for developmental reactions. The addition of small amounts of gaseous reagents to such reaction mixtures is often troublesome. Typical solutions to this problem involve rather complicated equipment (vacuum lines, gas manifolds, etc.) or are inconvenient and susceptible to significant errors (weighed amounts of condensed gases, etc.). Recently a convenient apparatus for automatic generation and addition of small amounts of gaseous reagents has been described (I). However, certain gases are not readily generated and cannot, therefore, be conveniently handled in this manner. A simple solution to this problem was developed by constructing a gas-tight syringe of 250 ml capacity from readily available laboratory apparatus1 (Fig. 1). A 250-ml class buret was used as the syringe barrel. We used a . bet fitted with a Luer Lock for attachment of the syringe needle, hut this is not essential since the needle may be attached to an ordinarv buret with a short leneth of rubber tubing.2 The plunger was machined from Feflon bar stock to fit loosely into the barrel. Two grooves were machined to accommodate elastomer O-rings (2). A small oil groove was cut between the two O-ring grooves. A hole was drilled and tapped to connect a n aluminum plunger rod. A section of plastic machined to fit the end of the buret was used to guide the plunger rod. Two small holes were bored in this guide to allow air to escape when withdrawing the plunger. The guide may he attached to the barrel with electrical tape. Before use, a small amount of inert oil is placed in the oil groove to lubricate the O-ring seals. The needle is attached, and the entire assembly tested for leaks by pushing the needle tip into a rubber stopper and depresk ~~b sing the plunger. It should be possible t o compress the air in the syringe to half its original volume -em m~ ordu.w without evidence of a leak. Bvnf The syringe is flushed and filled using the apnaratus shown in Firmre and t h e following proO-ring cedures
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Figure 1. 250-ml gas syringe.
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The supply hose from the gas pressure regulator is cannected to one arm of a "T". tube bubbler, the other arm of the "T" is capped with a rubber serum stopple, and the outlet is vented to a fume hood 13). When this assembly has been thorouehlv flushed with gaseous @agent, the needle of the gas syringe is inserted. and the svrinee is filled by slowly &th&aw-
Figure 2. Typical apparatus far flushing and filling thagas syringe
ing the plunger. The needle is then withdrawn from the bubbler, and the plunger is depressed, venting the reagent into the fume haad. This flushing procedure is repeated several times to remove air from the syringe. After flushing, the syringe is filled with the desired volume of the reagent gas, and the buret stopcock is clmed. Just before use, the stopcock is opened to purge the needle and allow the reagent to come to atmospheric pressure. As soon as the excess pressure is relieved, the needle is inserted through a serum stopple into the reaction' vessel, which should also be at atmospheric pressure. A mercury-filled bubbler serves as a simple differential manometer to indicate the messure within the reaet ~ vessel. m The plunger is then slowly depressed to the zero mark. and the syrmge rs left cunnwted to the reaction vrssrl u n t d rhr manometer mdicate.i atmoaphrrw pressure. T n e needle is withdrawn at this paint. We have successfully used this syringe to add gaseous olefins to hydroboration mixtures and to add gaseous polyhalomethanes toother systems (4,5). Acknowledgment The author wishes to thank the National Science Foundation for support through a traineeship (GZ-2001) administered by Purdue University and Professor Herbert C. Brown for guidance and encouragement. Literature Cited
and 242-45. (3) Molau, G.E.,andKe119r.R.T.,J C b .Educ. PZ.563(1965). (4) Brom. H. C.. "Hydraboration," W. A. Benjamin. Ine.. New Ymk, New York, 19E2: Brom. H. C.. "Boraoes in Organic Chemiavy." Cornell University Pros., Ifhaea,
New York, 1972. 15) B m m . H. C.. Carlson, B. A,. end finger. R. H., J Amer Chem. Soe., 93. 2070 (1971).
Gas-tight syringes are available from the Hamilton Company, Whittier, California, 90608; these are constructed of acrylic resin and are rather expensive. ZBurets of this type are available from Delmar Scientific Co., Maywood, Illinois, 60153, as an accessory for the Brawn HydroT h e volume of gas was cplculared from simple gar laws asauming ideal hehavior for the gases used. It is important that the inrtial and final pressures in the svrmae . . he ident~ralm order t u add the correct ambunt of gas. Volume 50,Number 3.March 1973
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