Synthesis and characterization of twenty-two purified polychlorinated dibenzofuran congeners

The identification of toxic polychlorinated dibenzofurans (PCDFs) in diverse environmental matrices requires the availability of purified standards for analytical, toxic, and biologic studies. This study reports the synthesis and characterization of 22 purified PCDF congeners by the base-catalyzed cyclization of their corresponding hydroxypolychlorinated biphenyl (PCB) precursors containing o-chloro and -hydroxy substituents on the two phenyl rings. The synthesis of the hydroxy PCBs (from their methoxy analogues) was accomplished by using two main routes, namely, (1) the diazo coupling of chlorinated anisidines and symmetrical chlorinated benzenes and (2) the diazo coupling of chlorinated anilines and chlorinated anisüles. By the judicious selection of the synthetic precursors it is conceivable that these schemes could be used to prepare most of the PCDF congeners.