An Alternative Procedure for Handling Borane Solutions Ann M. Fabirkiewicz Randolph-Macon Woman's College, Lynchburg, VA 24503
An experiment recently reported in this Journal' describes a procedure for canying out the hydroboratiod oxidation of several organic compounds that is practical for large organic laboratory sections. The borane solution is dispensed by TA's with syringes. It has beenmy experience that syringesused for handling borane solutions frequently "freeze", sometimes with the borane solution still inside. Also, repeated insertion of the syringe needle into the sure-seal bottle degrades both the seal and the borane solution. I have devised a way for my students to handle borane solutions without using a syringe and with minimal contact with the stock bottle. A
to 6 bubbler
flame-dried 50- or 100-mL graduated cylinder is capped with a 24/40 rubber sevtum that is wired in place. The reagent is transferrcd, u&n(:a double-ended nechle, ta th~ii kvaduated cyl~nderOne end of the doublr-mdcd needle IS inserted in& the solution. Nitrogen gas and a bubbler are used to provide the positive pressure needed for transfer. (See the figure.) When the desired amount has been transferred, the needle is removed from the solution, but not from the reagent bottle, and nitrogen is allowed to pass through the needle to flush it thoroughly. The same procedure is then used to transfer solution from the graduated cylinder to the reaction vessel. If several students are doing the experiment on the same day, enough borane solution for all is transferred to the graduated cylinder. In this way, the stock solution is handled only once. I have used the standard hydroborationloxidation proceduress with this technique in my advanced organic laboratory for several years with no mishaps. The students gain experience working in an inert atmosphere and confidence working with potentially dangerous solutions. I feel the technique can be readily adapted to Pickering's procedure, allowing TA's to dispense from a graduated cylinder rather than from the reagent bottle. Also, double-ended needles are less expensive than syringes and are usually more durable. Pickering, M. J. Chem. Educ. 1990, 67,436. Brown. H. C. OrganicSynthesis via Boranes;Wiley-Interscience: New York, 1975. 1
Transfer of a borane solution from the reagent bottle to a graduated cylinder by double-ended needle.
Volume 68 Number 7 July 1991
613
