The 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.
I. Introduction.
-Weakly alkaline aqueous solutions of arenediazonium salts are important in the synthesis of azo compounds, including the majority of technical azo dyes. On the other hand, it has been known qualitatively for many years [2] that their stability is lowest under these conditions. It is therefore surprising that the mechanisms of such decompositions have not been investigated in detail; however, the reactions which occur in such systems are very complex.
In the present paper we report on the equilibria and kinetics of the reactions of p-chlorobenzenediazonium ions in aqueous buffer solutions between pH 9.0 and 10.6 under strict exclusion of oxygen ( < 5 ppb of 0,). In the presence of even ' j Part Xv: s.