The rates and product distribution for the spontaneous dediazoniation of 2-, 3-, and 4-methylbenzenediazonium ions, OMBD, MMBD, and PMBD, respectively, in the presence of α-, β-, and γ-cyclodextrins (CDs) in aqueous acid are reported. No evidence of reaction between arenediazonium ions and CDs was found. Quantitative conversion to the phenol derivative, ArOH, is achieved for all diazonium ions, and observed rate constants, k 0, and product distributions are independent of both acidity and cyclodextrin concentration. All evidence is consistent with a D n + A n dediazoniation mechanism, that is, rate-determining formation of an aryl cation which reacts immediately, with low selectivity, with available nucleophiles. Data are discussed in terms of formation of an inclusion complex in which the methylbenzene portion of the arenediazonium ion is inserted, to some extent, in the CD cavity, the diazonium group being located in a water-rich region with similar properties to those of the bulk solvent. Results consistent with the D n + A n mechanism contrast with those in the literature, which indicate that cyclodextrins promote free-radical dediazoniations in a solvent where the ionic process is especially favored.

Rate constants for dediazoniation product formation and arenediazonium ion loss and product yields of solvolysis of o-methylbenzenediazonium tetrafluoroborate in acidic methanol-water mixtures at T ϭ 35ЊC are reported. Observed rate constants for diazonium ion loss and product formation are the same, increasing about 45% ongoing from water to methanol, and are not affected by added electrolytes like HCl, NaCl, and CuCl 2 . Only three dediazoniation products are detected, o-cresol, o-chlorotoluene, and o-anisole. All data are consistent with a rate-determining step formation of an aryl cation that reacts immediately with available nucleophiles. The selectivity of the reaction toward nucleophiles, S, which can be Correspondence to: C. Bravo-Diaz (cbravo@uvigo.es)