A Simple and Cost-Effective Technique for the Transfer of Air-Sensitive Solutions Laura J. Smith Vosejpka Alma College, Alma, MI 48801
The use of nitrogen-filled balloons for maintaining an inert atmosphere during the course of a reaction is a simple and inexpensive technique that organic chemists have relied upon for years. Due, initially, to fmancial and space constraints in our Advanced Inorganic Chemistry lab, we recently have applied this "balloon technology" to a number of standard Schlenk techniques with a great deal of success. The particular technique described below is a modification of the double-tipped needle technique for transferring air-sensitive liquids and solutions as described by Shriver (1). Our apparatus consists of a Teflon stopcock-equipped Schlenk flask (the 50-mL size is available for $59.96 from ChemGlass, although a traditional glass barrel stopcock would work as well), a 16-gauge, 24-in. double-tipped needle or cannula, a 1G20 gauge bleed needle and a balloon1 stretched over a s i n . piece of 60-mm i.d. red rubber vacnitrogen filled hill"""
uum tubing (see figure). To transfer solutions from the Schlenk flask to the round-bottomed flask, the balloon is filled with nitrogen, placed on the serrated, Teflon end of the stopcock arm, and the stopcock is opened slightly. The rate of addition is adjusted easily by gently squeezing the balloon. The elasticity of the balloon assures that positive pressure of nitrogen is always maintained and negates the need for an oil bubbler. Our technique has a number of advantages over the more traditional use of a stopcock equipped inert gas manifold. The first, obviously, is cost. The second is convenience. Direct connection access to an inert gas tank is not necessary; therefore, these techniques can be performed by any number of students on the benchtop (assuming that the solution being transferred is not toxic. Toxic solutions require that the bleed needle be connected to a trap of some sort.) The third, and unexpected result of our modification, is greater student understanding. By literally using a "hands-on" approach to adjusting flow rate, students gain a greate;understanding of ;he princ~plesof pressure differential mvolved in the transfer. We have found that addition rate is controlled more easily by squeezing a balloon than by adjusting the stopcock or the gas pressure a t the tank. In the course of our research in organometallicchemistry here a t Alma College, we have developed balloon modifications of a number of standard Schlenk techniques, including running a Schlenk column. We would be happy to share these with all interested parties. Literature Cited
50 mL fi flask
50 mL. 14120 tellon
1. Shtiver, D. F The Monipulafion of AirSznsitiur Compounds: Mdjraw-HW New Y d ,1969.
stopcock Schlenk flask
Balloon modified cannula transfer of an air-sensitve solution.
'We Lse Oua atex Da loons with a 12-m wal. tnickness purchased from the Aldr ch Chemica Company (cal # 215,498-91.
Volume 70 Number 8 August 1993 .
665
