71032-63-8Relevant 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.
