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A common practical question facing organic chemists when carrying out a chemical reaction is "When is the reaction complete?" The determination of this very important reaction parameter is generally not addressed in undergraduate organic chemistry courses in a practical sense. Normally, a reaction time is given to the student as part of a cookbook procedure. Undoubtedly, there are many reactions slow enough to explore reaction times within the time frame of undergraduate chemistry labs. However, there is a simpler way to introduce this idea while simultaneously providing a problem-solving experience for students that is rooted in real-world situations: Use incremental reagent addition to a rapid chemical reaction. A key reagent is added in increments, and the reaction is assayed after each addition. The end of the reaction is signalled by the disappearance of starting material as ascertained by TLC, IR, NMR, GC, or any technique one wishes to highlight.
In our introductory organic chemistry lab course we have used the oxidation of 9-fluorenol to 9-fluorenone by bleach (sodium hypochlorite) with monitoring by TLC as a teaching device with a problem-solving aspect. The students add NaOCl in small amounts to the starting material and determine for themselves when they have added enough reagent to complete the reaction. They cannot easily calculate the required stoichiometric amount of aqueous NaOCl due to the variable composition and decomposition rates of commercial bleach.
The oxidation of 9-fluorenol by this method is superior sup 2 from an environmental point of view to the chromic acid on amberlite method published previously (1).
EXPERIMENTAL PROCEDURE
Dissolve 50 mg of 9-fluorenol in 3 mL of acetone using a 10-mL round-bottom flask. Use 3 to 5 mu-L of this sample as a control for thin layer chromatography (TLC). Add to the flask 0.12 mL of glacial acetic acid, and start...