Dediazoniation of Arenediazonium Ions in Homogeneous Solutions. Part XVI. Kinetics and mechanisms of dediazoniation of p‐chlorobenzenediazonium tetrafluoroborate in weakly alkaline aqueous solutions under nitrogen gas

Abstract

SummaryThe kinetics of reactions of p-chlorobenzenediazonium ions in aqueous buffer solutions (pH 9.0-10.6) under N, (< 5 ppb of 0,) have been measured between 20 and 50°C. The formation of trans-diazotate is first-order with respect to the concentration of hydroxyl ions and to the equilibrium concentration of diazonium ions, if the diazonium ion+cis-diazotate equilibrium is considered as a fast prior equilibrium. This indicates that the p-chlorobenzenediazonium ion, in contrast to all previous investigations with the p-nitrobenzenediazonium ion and benzenediazonium ions carrying similar substituents with a -M effect, rearranges from the cis-to the trans-configuration as diazohydroxide and not as diazotate. The formation of trans-diazotate is catalyzed by carbonate and inhibited by hydrogen carbonate ions; mechanisms of these catalyses are discussed, and the solvent isotope effect KH20/KD20 measured by an 'H-NMR. technique reported. The kmetics of the dediazoniations can be analyzed as a mixture of two reactions, a relatively fast first reaction, reaction A, which is responsible for about 5% of the total reaction, and a second reaction F. Both are first-order with respect to diazonium ion; reaction A is also first-order in hydroxyl ions. There are some indications that reaction A corresponds to the hydrolysis of the diazonium ion to give eventually amine and nitrite ions. Reaction F shows a complex dependence on hydroxyl ions; it is related to the homolytic dediazoniation.

Spontaneous modification of glassy carbon surface with anthraquinone from the solutions of its diazonium derivative: An oxygen reduction study

“…Eliel et al [90] further proposed that disproportionation of ArN@NO gives the corresponding arylbenzene and regenerates ArN@NOH, thus providing a cyclic mechanism for radical generation. These reactions can take place in the pH range where steps (VIII) and (IX) are feasible and hence, depends on the acid-base properties of the intermediates [91,92]. A similar analysis for the spontaneous grafting of single-walled carbon nanotubes (SWCNTs) from the aqueous solutions of aryldiazonium salts has been suggested by Tour and co-workers [60][61][62].…”

Dediazoniations of Arenediazonium Ions in Homogeneous Solutions. Part XV. Products of dediazoniation of p‐chlorobenzenediazonium tetrafluoroborate in weakly alkaline aqueous solutions

“…publications concerning the kinetics of decomposition of this diazonium ion in the same pH-range [3] [4], we now report on the products formed under these conditions.…”

“…The rate of reaction is therefore independent of the hydroxyl ion concentration as long as the pH is kept below the pH range of the diazoniumlcis-diazotate equilibrium. The constant of this equilibrium is (pK, + pK2)/2= 10.84+ 0.02 at 25" and ionic strength I= 0.1 [3] [8].…”

Nucleophilic Aromatic Substitutions. Part XIV.. Investigation of the mechanism of hydroxy‐denitration of 4,2‐and 2,4‐chloronitrobenzenediazonium ions as a function of pH

“…pH=2, dediazoniations follow the heterolytic S,1 -like mechanism and that, with increasing pH, the rate increases to a maximum at medium to slightly alkaline pH-values. Under such conditions product ratios and kinetics are very sensitive to various additives and oxygen [6] [7]. C1DNP.-measurements [8] and kinetics indicate strongly that dediazoniation follows a homolytic pathway.…”

“…The numerical value (pK, + pK,+ pK3)/3 for the overall equilibrium 4 is therefore lower than (pK, +pK,)/2. Examples can be found in a review by &rba [21] and in a paper we published recently [7] on the equilibria of the pchlorobenzenediazonium ion: ( p K , +pK2)/2= 10.84 (25", Z=O,l); (pK, +pKZ+pK,)/3=9.75 (20°, Z=O,l);…”