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

✍ Scribed by Carlos Bravo-Díaz; Laurence S. Romsted; Mathew Harbowy; Ma. Emma Romero-Nieto; Elisa Gonzalez-Romero

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 133 KB
• Volume: 12
• Category: Article
• ISSN: 0894-3230
• DOI: 10.1002/(sici)1099-1395(199902)12:2<130::aid-poc107>3.0.co;2-9

✦ Synopsis

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 CuCl 2 concentrations at 60 °C were examined. Two main products were observed: p-nitrophenol (ArOH) and p-nitrochlorobenzene (ArCl). Trace amounts of nitrobenzene (ArH) and p-nitrofluorobenzene (ArF) were detected. Added CuCl 2 speeds the reaction and both the rate of dediazoniation and ArOH yield (unlike ArCl) are very sensitive to pH. The results 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 first order (with respect to PNBD) in the absence of and presence of CuCl 2 , except at low acidity and in the presence of low to moderate CuCl 2 concentrations. The non-first-order kinetics are attributed to a competing reaction between PNBD and the ArOH product. The results suggest a simple method for preparing halobenzenes in high yield.