Mechanism of oxidation of primary and secondary alcohols by oxopiperidinium salts

Conclusions

• 1. Oxidation of primary and secondary alcohols by oxopiperidinium salts clearly results from the transfer of an alcoholate anion and a hydride ion from the alcohol to the oxopiperidinium cation ($\begin{array}{*{20}c} \backslash \\ / \\ \end{array} \mathop N\limits^ + = O$). The primary product from the$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} \mathop N\limits^ + = O$ reduction is the hydroxypiperidine ($\begin{array}{*{20}c} \backslash \\ / \\ \end{array} N---OH$), which then reacts with the$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} \mathop N\limits^ + = O$ to form the nitroxyl radical.

• 2. The stoichiometry of the reactions of the oxopiperidinium salts with alcohols is determined by the rate of interaction of the$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} \mathop N\limits^ + = O$ with ROH, RO⁻ and$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} N---OH$ varying with the pH and the initial, concentrations in the system.

• 3. Alcohol oxidation by nitroxyl radicals in acid solution proceeds through radical disproportionation, followed by interaction of the$\begin{array}{*{20}c} \backslash \\ / \\ \end{array} \mathop N\limits^ + = O$ and the alcohol.