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

Abstract

SummaryThe products of decomposition of solutions of p-chlorpbenzenediazonium tetrafluoroborate in aqueous buffer solutions (pH 9.0-10.3; ionic strength 0.1-0.5) at 20.0" have been analyzed quantitatively. Up to eleven low molecular weight compounds could be identified besides the major product, the complex polymeric diazo tar. The distribution of products is influenced by trace amounts of oxygen as well as by p-chlorophenol and the radical trapping reagent iodoacetic acid. Mechanisms of formation of the products are discussed.1. Introduction. -The reaction products of arenediazonium ions in aqueous solutions depend on acidity, and three main areas of interest with respect to pH can be defined. In the case of the unsubstituted benzenediazonium ion heterolytic hydroxydediazoniation is dominant below about pH 4, and phenol is formed. At pH-values higher than 12, cis-benzenediazotate (originally called syn-diazotate) is formed; it is rearranged slowly into the trans-diazotate (anti-diazotate). In the intermediate pH-range a number of products can be detected, in particular the so-called diazo tars, i.e. macromolecular compounds of a complex structure which has not yet been investigated in detail2). For substituted benzenediazonium ions the above pH ranges are shifted to higher and lower values, depending on the basifying and acidifying character, respectively, of the substituents.The mechanisms of heterolytic hydroxydediazoniation and hydroxyaddition have been investigated in detail. In contrast, only a few mechanistic studies have been made of reactions of diazonium ions in the medium range of pH values (pH 6-11) in spite of the fact that solutions of diazonium salts are often used for the synthesis of azo dyes in precisely this pH range. The lack of data.on the fate of diazonium salts in slightly alkaline solutions is due to the complex mixture of products and to the difficulty in reproducing the kinetic data.

Dediazoniation of Arenediazonium Ions in Homogeneous Solutions. Part XVII. Kinetics and mechanisms of dediazoniation of p‐chlorobenzenediazonium tetrafluoroborate in weakly alkaline aqueous solutions in the presence of oxygen

“…As we have argued previously [ 2 ] , it can scarcely originate from a heterolytic hydroxydediazoniation as this reaction is, at 20", about 500 times slower [I61 than the reactions which we describe in this paper. In addition the product analyses [2] demonstrate that in the absence of 0, (< 5 ppb of 0,) only traces ofp-chlorophenol and its subsequent product of diazo coupling are found (<0.2%), whereas in the presence of 60 ppb or more 0, significant amounts ofp-chlorophenol and its azo Scheme I derivative are formed (> 3%). As Russel et al [ 171 have shown, aryl radicals react with O2 to form finally phenols and dihydroxybenzenes.…”

“…benzene can indeed be found in the products [2]. Bztnnetl et al and Cadogan et al [15] have demonstrated that iodobenzene is a scavenger for aryl radicals.…”

“…Possibly the other reaction products found by us [2] also catalyze the dediazoniation. It is, however, unlikely that they are as important as p-chlorophenolate ions.…”

“…-In previous papers we have described investigations of the structure and distribution of products formed in dediazoniations of p-chlorobenzenediazonium ions in weakly alkaline aqueous solutions in the presence and absence of 0, [2] and also the kinetics and mechanisms of these systems under N2 (< 5 ppb of 0,) [ 11 [3]. The analyses of the decomposition products [2] indicate that the mechanism of dediazoniations under these conditions is influenced by 0, present in the solution and in the supernatant atmosphere.…”

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

“…Below pH 6.5 n, and n, are 1 within the experimental limits; they are, however, greater than above pH 6.5. The following values are characteristic: 6.0 1.09 1.02 7.0 1.71 1.37 7.9…”