Dehydration of Vicinal Diols
A vicinal diol can be synthesized in various ways. Its dehydration leads to an enol that equilibrates with the corresponding aldehyde or ketone.
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In the example, cyclohexene is oxidized by a peracid (MCPBA, m-chloroperbenzoic acid) to the epoxide, which in aqueous acid is opened by attack of water from the opposite face to give trans-1,2-cyclohexanediol. In acid, one of the OH groups is protonated and leaves as water; loss of a proton from the neighboring carbon, the one bearing the other OH, gives the enol (cyclohex-1-en-1-ol), which tautomerizes to cyclohexanone, the more stable form of the keto-enol equilibrium.