Elimination Reactions
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Alcohols can also undergo dehydration to form alkenes
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Alcohol vapour is passed over a hot (600 C) catalyst of aluminium oxide (Al2O3) powder or pieces of porous pot
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Excess hot, concentrated sulfuric acid or phosphoric acid is used as a catalyst
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Phosphoric(V) acid is used an alternative dehydrating agent
Dehydration of ethanol using aluminium oxide as a catalyst forms ethene gas, which can be collected over water
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This is an example of an elimination reaction
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Elimination reactions involve a small molecule being formed as a by-product
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The water molecule is formed from the -OH group of the alcohol and the H+ from the acid catalyst
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The neighbouring hydrogen is then lost as a H+ ion, which regenerates the acid catalyst
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- The reaction and mechanism for the dehydration of propan-1-ol is shown below
Dehydration of propan-1-ol mechanism
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Alkenes produced by this method can be used to produce addition polymers without using monomers derived from crude oil