71032-61-6Relevant academic research and scientific papers
Vinylic Cations from Solvolysis. 29. Solvolysis of 9-(α-Bromoarylidene)anthrones as a Probe to the Reactivity - Selectivity Relationship in Solvolysis Reactions
Rappoport, Zvi,Apeloig, Yitzhak,Greenblatt, Jeremy
, p. 3837 - 3848 (2007/10/02)
The solvolyses of 9-(α-bromoarylidene)anthrones 5a (Ar=An), 5b (Ar=Tol), 5c (Ar=Ph), and 5d (Ar=o-An) in 1:1 AcOH-Ac2O/NaOAc and in TFE/2,6-lutidine and of 5a in buffered AcOH and 80percent EtOH were investigated.An extensive common ion rate depression by the formed or added Br- ion was observed.Selectivity constants α=kBr-/kAcO- and α'=kBr-/kTFE or kBr-/K80percentEtOH for competitive capture of the derived cations 14 by Br- vs.AcO- or the solvent were calculated.The α values in 1:1 AcOH-Ac2O, the α' values in TFE, and the reactivities (kt0 values) are structure dependent and follow the order 5a > 5d > 5b.The results for 5c are not sufficiently accurate for reliable selectivity determination.The nature of the capturing nucleophile in AcOH-containing media is discussed and evidence for product formation nearly exclusively from a solvolytically generated free vinyl cation in AcOH, AcOH-Ac2O, and TFE is given.Linear or nearly linear reactivity-selectivity relationships of log kt0 vs. log α or log α' for 5a, 5b, and 5d were obtained, but the selectivity differences are moderate in 1:1 AcOH-Ac2O and small in TFE.This behavior is discussed in relation to Ritchie's constant selectivity rule for stable cations and the linear reactivity-selectivity observed for less selective ions.It is suggested that the different selectivity relationships represent different regions of an overall nonlinear reactivity-selectivity plots for carbonium ion reactions.The merits and disadvantages of measuring selectivities by common ion rate depression are discussed.
Vinylic Cations from Solvolysis. 30. Bromide Exchange as a Reactivity-Selectivity Probe in Vinylic Solvolysis
Ginkel, Frits I. M. van,Hartman, Eppo R.,Lodder, Gerrit,Greenblatt, Jeremy,Rappoport, Zvi
, p. 7514 - 7519 (2007/10/02)
Simultaneous exchange with radioactive Br(-) and solvolysis of 9-(α-bromo-p-methoxybenzylidene)anthrone (3a), its p-methyl analogue (3b), and three α-anisyl-β,β-diarylvinyl bromides (5a, 5b, and 5c) in AcOH/NaOAc/Et4NBr were studied.The reactions proceed via free vinyl cations and the dependence of kt on the NaOAc concentration for 3a and 5a indicates the rare SN2(C+) mechanism.The selectivity constants of the derived cations toward bromide and acetate ions α = kBr/kOAc increase with the reactivity of RBr, both in the family of the α-aryl-substituted (3) and in the family of the β-aryl-substituted (5) derivatives.Consequently, the reactivity-selectivity relationship rather than Ritchie's constant selectivity relationship applies for solvolytically generated free triarylvinyl cations.The exchange-solvolysis method is compared with the method based on common ion rate depression as reactivity-selectivity probes for the vinyl cations formed in the solvolysis.The exchange-solvolysis method is more accurate and measures the selectivity and reactivity in independent processes.Caution should be exercised when comparing k1 and α values which are measured by the two different methods, due to unknown salt effects on the two parameters.
