Oxidation of Aniline under Modified Boyland-Sims Conditions

The Boyland-Sims peroxydisulfate oxidation is a highly effective method for the introduction of a hydroxyl function into aromatic amines. The simplicity of the process, as well as the absence of the need to protect sensitive functional groups, are the reaction's defining characteristics. Nevertheless, the low yield of the target products restricts the practical application of the reaction. The present study investigates the peroxydisulfate oxidation of aniline under modified conditions of the Boyland-Sims reaction. The yield and ratio of ortho- and para-aminophenols formed in the oxidation of aniline were found to depend on the reaction conditions. Previous studies on this reaction have been conducted at ambient temperature. It was determined that these temperature conditions are inadequate for the complete oxidation of aniline. It was found that increasing the temperature to 45°C resulted in a twofold increase (up to 35%) in the yield of reaction products, which, however, remains inadequate for the practical application of the reaction. Consequently, modifications to the Boyland-Sims reaction conditions were proposed. These comprised the use of metallophthalocyanine catalysts or a second oxidizing agent, hydrogen peroxide. Both modifications enabled a substantial augmentation in the yield of reaction products, ortho- and para-aminophenols. In the presence of metallophthalocyanines, the yield of intermediate 2(4)- aminophenylsulfates increased to 54-85%. Among the studied catalysts, cobalt phthalocyanine proved to be the most active. Its addition allowed increasing the yield of 2(4)-aminophenylsulfates up to 85%, while the ratio of ortho- and para-aminophenols in the mixture was shifted towards the para-isomer, with a ratio of 1:7. However, the utilization of a combination of two oxidizing agents, ammonium persulfate and hydrogen peroxide, led to the unexpected formation of para-aminophenol as the predominant reaction product, accompanied by the presence of trace amounts of the ortho-isomer.