Ch_322a_7.08

Ch_322a_7.08 - Dehydration of Alcohols Alkenes are also...

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Dehydration of Alcohols Alkenes are also generally prepared by the dehydration of alcohols in the presence of a strong acid. C C H OH H + heat C=C + H 2 O Sulfuric and phosphoric acids are often used for this reaction. Industrial processes use flow reactors with the alcohol in the gas phase passing over a solid Lewis acid such as alumina, Al 2 O 3 , with heating.
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Characteristics of the Dehydration Reaction (1) The conditions (acid strength and temperature) required for the dehydration depend on the structure of the alcohol. CH 3 CH 2 OH primary alcohol conc. H 2 SO 4 180 o C CH 2 =CH 2 + H 2 O CH 3 COH CH 3 CH 3 tertiary alcohol 20% H 2 SO 4 85 o C CH 2 =C CH 3 CH 3 + H 2 O R-C-OH R R tertiary alcohol > R-C-OH R H secondary alcohol R-C-OH H > H primary alcohol General Order of Reactivity
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(2) The alkene product mixture follows the Zaitsev rule --the alkene product with more alkyl substituent groups is favored. CH
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This note was uploaded on 07/22/2009 for the course CHEM 322AL taught by Professor Jung during the Summer '07 term at USC.

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Ch_322a_7.08 - Dehydration of Alcohols Alkenes are also...

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