A New, Jacketed Stirrer BearingISpacer Many reactions carried out in chemistry laboratories utilize a glass stirring shaft with a grease-lubricated bearing. In some eases, the solvents used (e.g., dichloromethane, toluene), especially a t reflux, can attack the grease in the hearing causing the lubricant to become thinner. This can result in the grease leaking out of the hearing, which can contaminate the reaction mixture and possibly cause the shaft to seize in the hearing. This situation is even more of a problem when apparatus such as a D e a n S t a r k trap is used, raising the condenser well above the bearing and allowing the refluxing vapors to contact the bearing long before the condenser. In some eases, a straight adapter can he used as a spacer tc raise the bearing closer to the height of the condenser, but this usually requires a long spacer, which can create several problems including a pronounced "wobble" of the stirring shaft. The use of a water-cooled bearing does not prevent the solvent vapors from reaching the grease and in some cases the cold bearing causes the grease to thicken, making stirring difficult. To alleviate these problems, we have designed a new, jacketed stirrer hearingispacer (see figure) which consists of a short, jacketed spacer attached to the bottom of a stirrer hearing. The design and use of this piece, to the best of our knowledge, is novel. A prototype was prepared for use in our laboratory and has proved to he very effective under various reaction conditions and with several different solvents (e.g., dichlaromethane, 2-hutanone, and ethanolic HCI). The jacketed spacer portion effectively prevents the solvent vapors from reaching the grease in the hearing without cooling the bearing, and the onepiece construction keeps the hearing as close to the reaction flask as possible. In situations where the stirring shaft would begin to seize up after one to two hours of reflux in a "typical" setup, use of this bearinglspaeer allowed refluxing for more than 12 hours with no sign of solvent contact with the grease. In conclusion, this hearingkpacer has proven to be very effective in preventing solvent vapors from contacting the grease in the bearing, thus preventing possible contamination of the reaction mixture and/or 'stirrer shaft seizing. Keith E. Goehring Hoechst-Roussel Pharmaceuticals, Inc. Rte. 202-206 Some~ille,NJ 08876
1000
Journal of Chemical Education
