Heterolytic dediazoniation of 2-, 3-, and 4-methylbenzenediazonium tetrafluoroborate in the presence of alpha-, beta-, and gamma-cyclodextrins

The rates and product distribution for the spontaneous dediazoniation of 2- , 3-, and 4-methylbenzene-diazonium ions, OMBD, MMBD, and PMBD, respectivel y, in the presence of alpha-, beta-, and gamma-cyclodextrins (CDs) in aqueo us acid are reported. No evidence of reaction between arenediazonium ions a nd CDs was found. Quantitative conversion to the phenol derivative, ArOH, i s achieved for all diazonium ions, and observed rate constants, k(0), and p roduct distributions are independent of both acidity and cyclodextrin conce ntration. All evidence is consistent with a D-n + A(n) dediazoniation mecha nism, that is, rate-determining formation of an aryl cation which reacts im mediately, with low selectivity, with available nucleophiles. Data are disc ussed in terms of formation of an inclusion complex in which the methylbenz ene portion of the arenediazonium ion is inserted, to some extent, in the C D cavity, the diazonium group being located in a water-rich region with sim ilar properties to those of the hulk solvent. Results consistent with the D -n + A(n) mechanism contrast with those in the literature, which indicate t hat cyclodextrins promote free-radical dediazoniations in a solvent where t he ionic process is especially favored.