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

The kinetics of reactions of p ‐chlorobenzenediazonium ions in aqueous buffer solutions (pH 9.0–10.6) under N 2 (< 5 ppb of O 2 ) 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 K H 2 O / K D 2 O measured by an 1 H‐NMR. technique reported. The kinetics 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.