REACTION OF DIAZONIUM SALTS WITH NUCLEOPHILES .8. IDENTITY OF RATE- AND PRODUCT-DETERMINING STEPS

The effects of several salts on the rates of disappearance of benzenediazonium ion in aqueous solution are studied. The effects are small, but at any concentration the rates increase in the order bisulfate < chloride < bromide < thiocyanate. Rates with various bisulfates are slower than in the absence of added salts. The rate reduction is attributed to the low reactivity of water solvating the cation, and hence the very small rate effect of solutions of sodium bromide or chloride is actually a combination of a retardation due to the sodium ion and an acceleration due to the chloride or bromide ion. These rate accelerations are at least enough to account for all the chlorobenzene or bromobenzene formed. Thus no products are determined by competitions after the rate-determining step–a conclusion supported by a simple reinterpretation of a great deal of earlier data. It is possible to account for the detailed shape of the plot of rate vs. salt concentration by a normal salt effect, so an earlier interpretation of this shape in terms of a spirocyclic diazirine cation intermediate is not supported. The relative reactivities of the different nucleophiles toward the diazonium ion differ very little, and it is shown that this unse-lectivity leads to an inherent and general difficulty in distinguishing between one-step reactions and two-step processes through a highly reactive intermediate. © 1969, American Chemical Society. All rights reserved.