Highly efficient and organic nitrogen-containing cation-promoted aerobic oxidation of alkylaromatics in the presence of N-hydroxyphthalimide

BACKGROUD: Direct oxidation of alkylaromatics to the corresponding aromatic ketone is an important process in the manufacture of perfumes, pharmaceuticals, flavors, dyes and agrochemicals. For example, tetralin is oxidized to produce 1-tetralinone, which is a key intermediate in the commercial production of 1-naphthol, 2-hydroxy-1-tetralone, aureolic acid antibiotics and other pharmaceuticals. RESULTS: In this investigation, it was found that alkylaromatics could be efficiently and selectively oxidized to the corresponding aromatic ketones when methyl violet was employed as a promotor in the presence of N-hydroxyphthalimide (NHPI); tetralin was oxidized with 89% conversion and 76% selectivity to 1-tetralinone under 0.3 MPa Of O-2 at 75 degrees C for 2.5 h. The effects of temperature, oxygen pressure, reaction time and additive inclusion were studied in detail. A possible reaction mechanism for tetralin oxidation has been proposed. CONCLUSION: It was demonstrated that methyl violet could efficiently promote the aerobic oxidation of alkylaromatics in the presence of NHPI under mild conditions. Further investigations indicated that the nitrogen cation had a crucial promotion effect in the oxidation process. (C) 2009 Society of Chemical Industry