Oxidative Ring-Cleavage of Catechol in meta-Position by Superoxide

Superoxide reacts with catechol in dimethylsulfoxide to form a yellow product. The structure of this product was established by different methods. UV-spectra of the yellow compound corre­ sponded under all circumstances to those of enzymatically produced 2-hydroxymuconic acid semialdehyde. In the presence of ammonia the product was converted to picolinic acid. The UV spectra, the retention times in GC and HPLC and the mass spectra after methylation corre­ sponded to those of authentic picolinic acid. Thus, the yellow reaction product was unequivocally identified as 2-hydroxymuconic acid semialdehyde. The formation of the me/a-cleavage product was only observed at low catechol concentrations ( < 2 m M ) , at higher concentrations the product was not formed. The reaction was complete within 10 min at room temperature. Spectroscopic data suggest a first intermediate in the reaction with X,