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5.4: Hydration of Alkenes

  • Page ID
    205341
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    This page looks at the production of alcohols by the direct hydration of alkenes - adding water directly to the carbon-carbon double bond.

    Manufacturing ethanol

    Ethanol is manufactured by reacting ethene with steam. The reaction is reversible.

    ethanoleq.gif

    Only 5% of the ethene is converted into ethanol at each pass through the reactor. By removing the ethanol from the equilibrium mixture and recycling the ethene, it is possible to achieve an overall 95% conversion. A flow scheme for the reaction looks like this:

    ethanolflow.gif

    Manufacturing other alcohols

    If you start from an unsymmetrical alkene like propene, you have to be careful to think about which way around the water adds across the carbon-carbon double bond. Markovnikov's Rule says that when you add a molecule HX across a carbon-carbon double bond, the hydrogen joins to the carbon atom which already has the more hydrogen atoms attached to it.

    Thinking of water as H-OH, the hydrogen will add to the carbon with the more hydrogens already attached. That means that in the propene case, you will get propan-2-ol rather than propan-1-ol.

    propeneh2o.gif

    The conditions used during manufacture vary from alcohol to alcohol.

    Contributors

    Jim Clark (Chemguide.co.uk)


    5.4: Hydration of Alkenes is shared under a not declared license and was authored, remixed, and/or curated by Jim Clark.

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