Question

which will be oxidised by HIO4

Answer 1

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.

Answer 2

The compounds that will be oxidised with $\[HI{O_4}\]$ are (c) I, II and IV.

Explanation:

• Periodic acid ($\[HI{O_4}\]$) oxidises and cleaves 1, 2-difunctional compounds.
• Therefore, it can oxidise vicinal diols, 1, 2-diketones, $\[\alpha \]$-hydroxy aldehyde or ketones.
• In the given compounds, $R-CO-CO-R$ (I) is 1,2-diketone. Therefore, it can be oxidised by $\[HI{O_4}\]$.
• The second compound $R-CO-CHOH-R$ (II) is $\[\alpha \]$-hydroxy ketone. Therefore, it can also be oxidised.
• The third compound $R-CHOH-\[C{H_2} - CHOH - R\]$ (III) is 1, 3-diol. Therefore, it cannot be oxidised with $\[HI{O_4}\]$
• The last compound $R-CHOH-CHOH-R$ (IV) is a vicinal diol. Therefore, it can be oxidised by $\[HI{O_4}\]$.
• Hence, the compounds that can be oxidised by $\[HI{O_4}\]$ are $\[R - CO - CO - R\]$ (I), $\[R - CO - CHOH - R\]$ (II) and $\[R - CHOH - CHOH - R\]$ (IV).

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