Evaluation of air-free glassware using the ketyl test

Air-free glassware and techniques are used in most organometallic research laboratories, but their relative effectiveness has not been well studied. We report a method for quantitatively comparing air and moisture exclusion by air-free glassware. Samples of benzophenone dianion in various glassware are monitored by video as their purple color is quenched. Numerical values for time until colorless are extracted from the video data and interpreted as a relative measure of air and moisture exclusion. Low pressure/vacuum (LPV) NMR tubes demonstrated by far the best performance, compared to a variety of Schlenk flasks and standard NMR tubes. The findings are of immediate practical use for synthetic chemists, and the evaluation methods can be used by individual laboratories to assess other conditions for air and moisture exclusion.