The addition of tert-butyl alcohol to a styrene epoxide and catalyst (p-toluenesulfonic acid) solution in acetonitrile accelerates the acid-catalyzed total conversion of epoxide and simultaneous oxygen absorption by this binary system (BS). The introduction of water into the alcohol solution of BS increases the oxidation rate to an even greater extent. Experiments with the indicator m-nitroaniline showed that the addition of alcohol and water decreased the deprotonating ability, i.e., the acidity of the solution. The attempt was made to rationalize the paradoxical situation, at which the decline in acidity is accompanied by enhancement of the acidcatalyzed reaction of the epoxide conversion and oxidation, in terms of the participation of the protonated alcohol in the intermediate complex with epoxide.