This lab exercise uses air-stable compounds (polyhalomethanes) to demonstrate trap-to-trap distillation, a technique used to separate air-sensitive compounds. The apparatus (including part numbers from CHEMGLASS) is described. In addition, slush baths are employed, which are a novelty for our Inorganic Laboratory course and a source of amazement for the students. The separation of the compounds (the percentage each compound in each trap) is determined by 1H NMR.
I would appreciate anyone who tries this exercise to let me know how well it worked. Having an average enrollment of six students (who work in pairs), I therefore only obtain three sets of results annually. Thank you in advance!
Students will learn how to separate volatile compounds via condensation in sequentially cooler low-temperature baths. Also, students will learn how to prepare slush baths and de-gas solutions via freeze-pump-thaw cycles, and, for most students, this may be their first opportunity to integrate an NMR spectrum. Finally, this exercise may serve as a general introduction to the manipulation of a Schlenk line. (For a more formal introduction to a Schlenk line, see: Davis, C. M.; Curran, K. A. “Manipulation of a Schlenk Line: Preparation of Tetrahydrofuran Complexes of Transition-Metal Chlorides.” J. Chem. Educ. 2007, 84, 1822-1823.
Equipment typically found in an Inorganic Laboratory: a Schlenk line, round-bottomed flasks, syringes, NMR tubes.
Special glassware (from CHEMGLASS): customized U-tubes, one-arm Hi-Vac valves, and T-shaped connectors. (Details of the custom order for the U-tubes are included in the file, as are parts numbers for the other pieces.)
A pair of students should be able to complete this exercise in one three-hour session.