Dehydration of Methylcyclohexanols VI

Besides the structure of the alcohol, what other variables may be explored?


1)      One variable for this reaction that could be investigated is the nature of the catalytic acid. Aqueous acids, such as the 85% H3PO4 typically used for this experiment, contain some water which is also product of the reaction. I may also add that, the amount of acid is not always in catalytic proportion to the substrate. In my current protocol 0.075 moles of acid is used to dehydrate 0.2 moles of alcohol. Non-aqueous acids may give different results. Acidic resins are an interesting substitute for aqueous acids. For example, John Ludeman and Kurt Field of Bradley University presented a poster at the 2006 ACS Great Lakes Regional Meeting on the use of Dowex 50WX2-100, Amberlite IRC-50S, and Amberlyst 15, for the dehydration of alcohols.


2)      Another variable would be the reaction conditions. In the current paradigm, the alkene is distilled away from the reaction mixture. Presumably, it is being distilled away as it is formed. An ad-hoc observation is that students seem to get somewhat different product ratios if they distill is carefully or if they “crank up the heat” and distill it quicker. What if the reaction mixture was refluxed to equilibrium before distillation? Would we see more thermodynamic products?


3)      Reaction conditions could be changed in other ways too. Microwave irradiation is currently being explored as an alternative to heating reactions. Possibly, sonication could also be performed on the alcohol.


4)      Another avenue to explore may be different strategies to push the reaction towards the products other than distilling off the alkene. For example, removing water with molecular sieves may be tried.


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