The liquid-phase oxidation of acenaphthene in the presence of tetraethyl and tetrabutyl ammonium halides proceeds with chain initiation via degenerate branching on a secondary hydroperoxide - acenaphthyl-9-hydroperoxide (AHP-9). In the series of salts investigated, change in the cation had virtually no effect on the activity of the salt, while variation in the anion indicates that, under identical oxidation conditions (a constant concentration of the catalyst and acenaphthene and a constant reaction time), the degree of conversion of the hydrocarbon increases in the order iodide < bromide < chloride with an almost identical selectivity of the reaction with respect to the hydroperoxide formed. When halides of quaternary ammonium salts are used, oxidation begins to develop actively from almost the first minutes, and in most cases the maximum rate of the reaction is rapidly attained. The selectivity of the process with respect to the hydroperoxide depends on the conditions and varies in a wide range (from 5 to 70%).