Rates and pH-dependent product distributions of the CuCl2-catalyzed dediazoniation of p-nitrobenzenediazonium tetrafluoroborate in aqueous acid

The rates of formation and yields of products from the dediazoniation of p- nitrobenzenediazonium tetrafluoroborate (PNBD) in aqueous solutions over a range of HCl, NaCl and CuCl2 concentrations at 60 degrees C were examined. Two main products were observed: p-nitrophenol (ArOH) and p-nitrochlorobenz ene (ArCl). Trace amounts of nitrobenzene (ArH) and p-nitrofluorobenzene (A rF) were detected. Added CuCl2 speeds the reaction and both the rate of ded iazoniation and ArOH yield (unlike ArCl) are very sensitive to pH. The resu lts are completely consistent with the heterolytic dediazoniation mechanism , i.e. rate-determining formation of a highly reactive aryl cation followed by competitive formation of dediazoniation products. PNBD kinetics are fir st order (with respect to PNBD) in the absence of and presence of CuCl2, ex cept at low acidity and in the presence of low to moderate CuCl2 concentrat ions. The non-first-order kinetics are attributed to a competing reaction b etween PNBD and the ArOH product. The results suggest a simple method for p reparing halobenzenes in high yield. Copyright (C) 1999 John Wiley & Sons, Ltd.