94929-78-9Relevant academic research and scientific papers
Solvolytic Generation of α-Sulfonyl and α-Sulfinyl Carbocations
Creary, Xavier,Mehrsheikh-Mohammadi, M.E.,Eggers, Mark D.
, p. 2435 - 2442 (2007/10/02)
A series of mesylates of general type ArC(CH3)(SO2Ph)OMs, 14, have been prepared and studied under solvolytic conditions.The Hammett p value in methanol is -7.98.A solvent effect study on 14b, where Ar=p-CH3C6H4, gave a good correlation with YOTs values and an m value of 0.85.These data were interpreted in terms of the involvement of α-sulfonyl-substituted carbocations, which have a large demand for aryl group stabilization.In solvolyses of 14b, capture of the α-sulfonyl carbocation by acetic or trifluoroacetic acid gave simple substitution products which could be isolated.In alcohol solvents subsequent unimolecular loss of benzenesulfinate ion from the initially formed α-alkoxy sulfone led ultimately to the formation of ketones or ketals.Analogous loss of benzenesulfinate from the primary product is also seen on prolonged reaction of 14b in carboxylic acid solvents.Solvolyses of a series of α-bromo sulfoxides of general structure ArC(CH3)(SOPh)Br, 35, also proceed via the intermediacy of carbocations.The demand for aryl stabilization in these α-sulfinyl cations is also quite large as evidenced by the p value of -7.18 in trifluoroethanol.The trifluoroethanolysis rate of 35b, where Ar=p-CH3C6H4, is 1.4x105 times slower at 25 deg C than that of the α-H analogue ArCH(CH3)Br, 29.This, along with the large negative p value, implies that the interaction of the sulfur nonbonding electrons with the adjacent cationic center is of minimal importance in the α-sulfinyl carbocation derived from 35b.These data conflict with previous suggestion that α-sulfinyl cations are greatly stabilized by the sulfur nonbonding electrons.Suggestions are offered to explain this apparent conflict.The relative reactivities of a series of bromides containing electron-withdrawing groups have been determined in the common solvent trifluoroethanol in order to evaluate the effect of these groups on the rate of carbocation generation.The relative reactivity order for sovolyses of substrates of general type p-CH3C6H4C(CH3)BrE, where E is an electronegative group, is COPh>PO(OEt)2>CN>SOPh>CF3>SO2Ph.
Reactions of Carbanions with Electron Acceptors
Bordwell, Frederick G.,Clemens, Anthony H.,Smith, Donald E.,Begemann, John
, p. 1151 - 1156 (2007/10/02)
Second-order rate constants for reactions of families of 9-substituted fluorenide ions, 9-R-Fl(-), and related carbanions in Me2SO solution with the electron acceptors PhSO2CH2Br, PhSO2CH(Ph)Br, PhSO2C(Me)(Ph)Br, Me2CBr2, Me2C(NO2)X, PhS(O)CH2Cl, Me2C(SO2Ph)2, and Ph2I(+)Cl(-) have been measured.The carbanions used varied in basicity over a range of about 20pKHA units.For a given family, Broensted plots of log k vs. pKHA were linear, with slopes usually near unity.The relative order of rate constants correlated for the most part with the order of reduction potentials of the electron acceptors.The carbanions were converted by the electron acceptors to dimers, i.e., 9-R-Fl- -> (9-R-Fl)2, by way of a single electron transfer (e-T) mechanism.The Broensted lines for the e-T reactions of the GC6H4C(Me)CN- ion family (G = p-Cl, H, and p-Me) and the 9-t-BuFl- ion family were displaced below that of the 9-MeFl- ion family (slower rates); the kinetic points for PhC(Me)SO2Ph- and Ph2CSO2Ph- ions fell near the 9-t-BuFl- ion family line.It is demonstrated that carbanions too weakly basic to undergo thermal e-T with a given electron acceptor can be made to undergo comparable e-T reactions under photostimulation.
