Ch15: Oxidation cleavage of 1,2-diols

Chapter 15: Alcohols, Diols and Thiols

Oxidative Cleavage of Diols

periodic acid cleavage of 1,2-diols

Reaction type: Oxidation-reduction

Summary

1,2- or vicinal diols are cleaved by periodic acid, HIO₄, into two carbonyl compounds.
The reaction is selective for 1,2-diols.
The reaction occurs via the formation of a cyclic periodate ester (see right).
This can be used as a functional group test for 1,2-diols.
The products are determined by the substituents on the diol.

QUESTIONS:
Can you recall a reaction that forms carbonyl groups via cleavage of an alkene ? ANSWER
How are 1,2-diols made from alkenes ? ANSWER
What are the oxidation states of the iodine in HIO₄ and HIO₃ ? ANSWER

PERIODATE CLEAVAGE OF 1,2-DIOLS
The mechanism is not trivial, so attention here is focussed on the actual cleavage step. Prior to this, the alcohol reacts to form a cyclic periodate ester (shown). The periodate ester undergoes arearrangement of the electrons, cleaving the C-C bond, and forming two C=O.