Dediazoniations of Arene Diazonium Ions in Homogenous Solution. Part IV: Change‐over from a heterolytic to a homolytic mechanism in 2,2,2‐trifluoroethanol pyridine mixtures

Abstract

Sunzmary. There are only two dcdiazoniation products of benzenediazonium tetrafluoroborate in Z,Z,Z-trifluoroethanol (TFE), namely phenyl 2,2,2-trifluoroethyl ether (1) and fluorobenzenc (2). The reaction kinetics are strictly first-order with respect to the diazonium salt. The addition of increasing amounts of pyridine to the system results in a gradual decrease in the yields of 1 and 2 and an increase in the yields of the homolytically formed products, benzene (3), biphenyl (4), isomeric phenylpyridines (5) and diazo tar (6). The reaction kinetics show that the rate of dediazoniation of the benzene diazonium salt increases with increasing amounts of pyridine. The reaction with added pyridine is no longer first-order with respect to the diazonium ion.The product analyses and the kinetic data are consistent with the view that in pure TFE this diazonium salt decomposes completely by a heterolytic mechanism. The addition of pyridinc brings about a competitive homolytic mechanism which becomes increasingly dominant as the concentration of pyridine increases.

Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part IX. Spectral Evidence for a Homolytic Mechanism Involving Pyridine Complexes

“…We conclude therefore that tlie physical evidence provided by this study corroborates the initial interpretation [6] which was based solely on the kinetics and products of the reaction. Moreover, the suggestions of Abrarnovitch et al [15] on the nature of tlie interaction of diazonium salts and pyridine now seem more secure.…”

“…Consistent with this interpretation was the finding that the higher the temperature (-20, -10, O O ) , the faster the maximal absorption was attained and likewise the consequent decrease was faster. Since the nature and amounts of the reaction products are not sufficiently determined [6], no compensation for their possible absorption could be applied to the observed spectra.…”

Dediazoniation of Arenediazonium Ions. Part XIX. Effect of thiocyanate ion in the reactions of 2,4,6‐trimethylbenzenediazonium tetrafluoroborate in 2,2,2‐trifluoroethanol

“…Confidence limits: 95% counter-ion and the solvent, respectively. Their ratio is comparable to that observed in the dediazoniation of benzenediazonium tetrafluoroborate (2) in TFE (34.5% C6H5F, 62.3% C6HSOCH2CF3) [17] indicating that in this case the product composition depends more on the reaction medium than on the structure of the substrate'). When KSCN is added to TFE thiocyanate ions compete with the solvent molecules, resulting in lower yields of the solvolysis product and the reaction product with the counter-ion.…”

Dediazoniation of Arenediazonium Ions in Homogeneous Solution. Part XII. Solvent effects in competitive heterolytic and homolytic dediazoniations

“…This is corroborated by results from other investigations. 1) Addition of pyridine to TFE in the dediazoniation of benzenediazonium tetrafluoroborate increases the overall rate and yields products typical of homolytic decomposition [6]. In addition, the kinetics change from strictly first-order in pure TFE to a nonintegral order between 0 and 1 (depending on the pyridine concentration) indicating a chain reaction.…”