Chemical reaction in which water is produced as a byproduct
This article is about chemical reactions resulting in the loss of water from a molecule. For the removal of water from solvents and reagents, see
Desiccation.
The classic example of a dehydration reaction is the
Fischer esterification, which involves treating a carboxylic acid with an alcohol to give an ester
RCO2H + R′OH ⇌ RCO2R′ + H2O
Often such reactions require the presence of a dehydrating agent, i.e. a substance that reacts with water.
Alkenes can be made from alcohols by dehydration. This conversion, among others, is used in converting biomass to liquid fuels.[2] The conversion of ethanol to
ethylene is a fundamental example:[3][4]
CH3CH2OH → H2C=CH2 + H2O
The reaction is accelerated by
acid catalysts such as
sulfuric acid and certain
zeolites.
These reactions often proceed via carbocation]]ic intermediates as shown for the dehydration of
cyclohexanol.[5]
Some alcohols are prone to dehydration. 3-Hydroxylcarbonyls, called
aldols, release water upon standing at room temperature:
RC(O)CH2CH(OH)R' → RC(O)CH=CHR' + H2O
The reaction is induced by dehydrating reagents. For example, 2-methyl-cyclohexan-1-ol dehydrates to 1-methylcyclohexene in the presence of
Martin's sulfurane, which reacts irreversibly with water.[6][7]
^Roden, Brian A. (2001). "Diphenylbis(1,1,1,3,3,3-hexafluoro-2-phenyl-2-propoxy)sulfurane". Encyclopedia of Reagents for Organic Synthesis.
doi:
10.1002/047084289X.rd409.
ISBN0471936235.