Dehydration - 1 Experiment 9: Dehydration of...

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1 Experiment 9: Dehydration of Methylcyclohexanols You will carry out the dehydration of either 2-methylcyclohexanol or 4- methylcyclohexanol by heating the alcohol in the presence of phosphoric acid: CH 3 OH CH 3 OH or H 3 PO 4 C 7 H 12 + H 2 O methylcyclohexenes ! The yield of this reaction will be increased if the alkenes are removed as they are produced, thus shifting the equilibrium to the right. For this reason, the reaction will be carried out in such a way that the alkene products distill out of the reaction mixture as they are formed. The products of this elimination reaction can include the following isomers: CH 3 CH 3 CH 3 1-methyl cyclohexene 3-methyl cyclohexene 4-methyl cyclohexene Elimination reactions such as this can proceed by different mechanisms. Direct elimination of water from 4-methylcyclohexanol would produce 4-methylcyclohexene, while direct elimination of water from 2-methylcyclohexanol would produce 1- and 3-methylcyclohexene. In the latter instance, the product that is favored by the reaction might be determined by Zaitzev's rule, which states: when HZ is removed from a species to form an alkene, hydrogen is lost preferentially from the carbon atom, of those adjacent to the carbon atom bonded to Z, that has fewer hydrogens. Thus, if Zaitzev's rule is followed for the dehydration of 2-methylcyclohexanol, then 1-methylcyclohexene would be the favored product. Alternatively, elimination reactions can occur via the formation of a carbocation and subsequently, rearrangements can take place. This sort of mechanism would result in the formation of 1- and 3-methylcyclohexene, in addition to 4- methylcyclohexene, from the dehydration of 4-methylcyclohexanol. Physical Properties
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This note was uploaded on 11/10/2010 for the course CHE 201 taught by Professor Bong during the Spring '08 term at SUNY Buffalo.

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Dehydration - 1 Experiment 9: Dehydration of...

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