Oxymercuration-Demurcuration and Hydroboration

The Markovnikov and anti-Markovnicov addition on water on 1-methyl-cyclohexanol.

Spring 2015

Abstract

The overall objective of this lab was to perform alkene addition reactions using two different methods: The oxymercuration demercuration and the hydroboration oxidation of 1-methylcyclohexene. Both of which are supposed to give two different regiochemical outcomes. It was hypothesize that 1-methylcyclohexene would give a regioselective outcome in the oxymercuration-demercuration experiment because of the competition between the tertiary carbocation and the secondary carbocation and therefore give a greater yield of 1-methycyclohexanol. It was also hypothesized that 1-methylcyclohexene would be both regioselective in the hydroboration-oxidation reaction due to the lack of enormity of borohydride and stereospecific due to the maintenance of stereochemistry as the alkyl group is transferred to the hydrogen peroxide ion. We therefore expected two products: 1-methylcyclohexan-2-ol and 1-methylcyclohexan-1-ol. In order to accomplish the objective several purification methods were used : ether extractions, drying over magnesium sulphate and the rotovaping of products. Results showed that oxymercuration is regiospecific. A 43.8% yield was obtained of which 99.6% was mainly 1-methylcyclohexanol and the other 0.4% was 1-methylcyclohexene. In the hydroboration-oxidation reaction, a 37.7% yield was obtained. The composition of this product was only 12.2% of the expected trans-2-methylcylohexanol, 16.7% of 1-methylcyclohexanol and the rest was mainly contamination. In order to identify the products, Infrared spectroscopy, nuclear magnetic resonance and gas chromatography were performed. Conclusion : A reaction will always use the more favorable pathway unless it is given energy which might enable it to use a less favorable pathway. In the Hydroboration-oxidation reaction for example, the markovnikov addition product is seen due warm reaction conditions....