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

Abstract

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.

Effects of Ascorbic Acid on Arenediazonium Salts Reactivity: Kinetics and Mechanism of the Reaction

“…Chromatographic kinetic data for all dediazoniation products were obtained according to a well-established procedure [46] [47] by quenching the dediazoniation reaction at convenient times with an aliquot of an aq. stock soln.…”

“…The presence of unknown products in dediazoniations has already been reported for other dediazoniations [15] [41] [47] under different experimental conditions. We assume that, whatever the mechanism is for formation of the unknown product, it is a competitive reaction leading to a reduction in the total observed yields, which are calculated on the basis of the initial ArN 2 concentration.…”

Spectroscopic studies of arenediazonium ion stability in surfactant solutions

“…(3)) from which the activation enthalpies and entropies of arenediazonium ion decomposition were estimated. BD ion, or of arenediazonium ion bearing the electron-releasing CH 3 − group [11]. The next factor influencing the dediazoniation reaction, investigated by us is temperature.…”

“…In 1940, Hammett [5] postulated a slow unimolecular heterolytic dissociation of arenediazonium ions into aryl cations and N 2 , and experimental support was provided [6]. The studies of these important reactions were continued by Zollinger [4,7,8] and other investigators [9][10][11][12].…”

Antagonistic Effect of Acetates in C–N Bond Formation with In Situ Generated Diazonium Salts: A Combined Theoretical and Experimental Study

“…The latter is formed by the reduction of the diazonium salt and should involve a radical intermediate. The reduction of diazonium salts by alcoholic solvents (here methanol) by de-diazoniation through a homolytic pathway can happen in neutral, [33][34][35][36][37] basic, [38][39][40][41] or acidic [42][43][44][45][46][47][48] media in the presence or absence of water, and the previous work by DeTar and co-workers [39,40,47] showed that it is favored by the presence of acetate in methanol, resulting in the formation of arene and formaldehyde.…”