The traditional laboratory experiment that explored the dehydration of cyclohexanol involved mixing together cyclohexanol and about a half-molar equivalent of concentrated acid, heating on a hotplate, and carefully distilling the product as it was created by maintaining the pot temperature below that of the boiling point of cyclohexanol. This procedure can be quite long for the more timid students, and really only answers the question “can you make cyclohexene”. Using the monomode microwave, we determined the settings for running the reaction at two different temperatures, 70<sup>o</sup>C and 100<sup>o</sup>C, to allow exploration of how Gibbs free energy governs the thermodynamics of a reaction. The monomode settings that were explored used 5W and 10W, included a two minute ramp to reach the target temperature, and were held at that temperature for different amounts of time. After the product was neutralized, isolated, and washed, percent cyclohexene versus hold time was graphed to determine when equilibrium was reached for each temperature and to determine the percent cyclohexene at equilibrium. These findings showcased what students would find by performing Spartan calculations or a computer search about the heats of formation of cyclohexanol, cyclohexene, and water. This allows students to both theoretically determine and experimentally observe how the dehydration of cyclohexanol to cyclohexene and water is endothermic. This obstacle then leads to exploration of Le Chatelier’s principle, and determination of how to push the reaction towards formation of cyclohexene. Students can explore Le Chatelier’s principle by carrying out a distillation of their microwave product or by seeing what happens when the reaction temperature is raised. The distillation of microwave product yielded very pure cyclohexene without needing a delicate hand at the hotplate. These monomode experiments were complete in 9-12 minutes from start to finish in the microwave, which is much shorter than a 60 to 90 minute distillation that was common for the traditional experiment. The shorter reaction time will allow students to explore multiple conditions and iterations of the reaction, and it will also allow deeper exploration of both Gibbs free energy and Le Chatelier’s principle.

Modifying the dehydration of cyclohexanol so as to become student centered

251st National Meeting (2016)

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