13948-08-8Relevant articles and documents
Electrochemistry of Carbonium Ions in Acidic Media. 1. Triphenylmethyl Ion in Aluminum Chloride Containing Melts
Luer, Garth D.,Bartak, Duane E.
, p. 1238 - 1243 (1982)
The electrochemistry of the triphenylmethyl carbonium ion (1) has been studied in a room-temperature aluminum chloride containing melt.Formation of 1 is dependent on the acidity or pCl of a molten aluminum chloride/n-butylpyridinium chloride (1:1) binary mixture.The equilibrium constant for reaction 1 is 20.4 +/- 0.3 mol L-1 at 40 deg C as determined by spectroscopic techniques.Formation of 1 from triphenylmethyl chloride is too slow to quantitatively determine a rate constant (kf) by conventional electrochemical techniques.Cyclic voltammetric and controlled-potential coulometric data reveal that 1 is reduced in an one-electron process to a triphenylmethyl radical (2).Formation of 2 in the AlCl3 melt is verified by ESR spectroscopy.Dimerization of 2 produces an electrochemically oxidizable form of 1-(diphenylmethylene)-4-(triphenylmethyl)-2,5-cyclohexadiene (3); the rate constant for the dimerization of 2 is 1.33 +/- 0.08 * 103 1 mol-1s-1 at 40 deg C.Workup of an exhaustively electrolyzed solution of 1 in the melt produces triphenylmethane, which is the result of proton isomerization of 3.
Kinetic, thermodynamic and mechanistic studies on the reduction of carbenium ions by NAD(P)H analogues
Cheng, Jin-Pei,Lu, Yun
, p. 577 - 584 (1997)
Hydride transfer mechanisms of the reductions of xanthylium ion by NAD(P)H analogues (i.e. BNAH, HEH and AcrH2) were investigated. Both the kinetic observations and an analysis of thermodynamic driving forces for each mechanistic step in all the possible mechanisms indicate that the reductions are initiated by a rate-determining electron transfer, followed by a fast hydrogen atom abstraction. The mechanism of the reductions of 9-phenylxanthylium and triphenylmethylium ions by BNAH were also investigated and are similarly discussed.
Rates of C-S bond cleavage in tert-alkyl phenyl sulfide radical cations
Baciocchi, Enrico,Del Giacco, Tiziana,Gerini, Maria Francesca,Lanzalunga, Osvaldo
, p. 641 - 644 (2006)
Radical cations of tert-alkyl phenyl sulfides 1-4 have been generated photochemically in MeCN in the presence of the N-methoxyphenanthridinium cation (MeOP+), and the rates of C-S bond cleavage have been determined by laser flash photolysis.
1H and 13C NMR detection of the carbocations or zwitterions from Rhodamine B base, a fluoran-based black color former, trityl benzoate, and methoxy-substituted trityl chlorides in the presence of alkali metal or alkaline earth metal
Hojo, Masashi,Ueda, Tadaharu,Yamasaki, Masanori,Inoue, Akihiko,Tokita, Sumio,Yanagita, Mitsuhiro
, p. 1569 - 1576 (2002)
The cleavage of C-O bonds in two fluoran-based dyes by the addition of alkali metal (M+ = Li+, Na+) and alkaline earth metal (M2+ = Mg2+, Ba2+) perchlorates in acetonitrile solution was exa
Straightforward formation of carbocations from tertiary carboxylic acids: Via CO release at room temperature
Bartalucci, Niccolò,Pampaloni, Guido,Marchetti, Fabio,Bortoluzzi, Marco,Zacchini, Stefano
supporting information, p. 1574 - 1577 (2019/04/02)
We report an unprecedented mode of reactivity of carboxylic acids. A series of tertiary carboxylic acids, containing at least one phenyl α-substituent, undergo loss of carbon monoxide at room temperature (295 K), by a one pot reaction with 0.5-1 molar equivalents of WCl6 in dichloromethane. A plausible mechanism for the Ph3CCO2H/WCl6 reaction, leading to [CPh3][WOCl5] and Ph3CCl, is proposed on the basis of DFT calculations. The analogous reactions involving CEt(Ph)2CO2H, CMe(Ph)2CO2H and CMe2(Ph)CO2H selectively afforded stable hydrocarbons (alkene or indene, depending on the case), apparently resulting from the rearrangement of elusive tertiary carbocations.
"naked" Lithium Cation: Strongly Activated Metal Cations Facilitated by Carborane Anions
Kitazawa, Yu,Takita, Ryo,Yoshida, Kengo,Muranaka, Atsuya,Matsubara, Seijiro,Uchiyama, Masanobu
supporting information, p. 1931 - 1935 (2017/02/26)
Experimental and spectroscopic studies revealed unprecedented reactivity of a "naked" lithium cation with very weakly coordinating anions, including carborane anions. The superactivated lithium cation has greatly enhanced Lewis acidic character and mediates various organic reactions such as carbonyl-ene reaction, NBS-bromination of unactivated aromatics, and Friedel-Crafts alkylation, which are not promoted by conventional lithium salts. Chemical robustness of the counteranion also plays an important role in the chemistry of the strongly activated lithium cation.
The Tris(2-thienyl)methyl Cation Problem. A Nuclear Magnetic Resonance Spectroscopic Study
Abarca, Belen,Asensio, Gregorio,Ballesteros, Rafael,Varea, Teresa
, p. 3224 - 3229 (2007/10/02)
A series of homologues of the trityl cation obtained by total or partial substitution of the phenyl rings for 2- or 3-thienyl groups has been studied by 1H and 13C NMR.In general, the spectral parameters found follow the expected trends.However, a most unexpected effect is found in the transformation of tris(2-thienyl)carbinol (1d) into tris(2-thienyl)methyl cation (2d) , since the increase of the total chemical shift (ΔΣδ) associated with the ionization is as low as 105 ppm.To account for this observation, several hypotheses are discussed including the possibility of through-space charge delocalization by the three sulfur atoms and the interaction of the thiophene rings in an alternate conformation.
Heterolysis and homolysis energies for some carbon-oxygen bonds
Arnett, Edward M.,Amarnath, Kalyani,Harvey, Noel G.,Venimadhavan, Sampath
, p. 7346 - 7353 (2007/10/02)
Methods described previously for obtaining heterolysis (ΔHhet) and homolysis (ΔHhomo) enthalpies for bonds that can be cleaved to produce resonance-stabilized carbenium ions, anions, and radicals are extended to the study of carbon-oxygen bonds through the reactions of resonance-stabilized carbenium ions with substituted phenoxide ions. Titration calorimetry was used to obtain the heat of heterolysis, and the second-harmonic ac voltammetry (SHACV) method was used to obtain reversible oxidation potentials for the anions. In several cases, the electrode reactions were so fast that reversible potentials were obtained only with the greatest difficulty. Nonetheless, there is remarkably good agreement between these oxidation potentials for phenoxide ions obtained by electrochemical methods in sulfolane solution and those reported by others using entirely different techniques in different media. Such agreement provides unprecedented evidence for the soundness of the various methods used to study redox potentials of organic ions and radicals. As before, a wide variety of correlations was tested between ΔHhet and ΔHhomo. These two properties showed little correlation with each other, but ΔHhet gave good correlations between many properties for which neutral species are converted into ions or vice versa, such as redox potentials of both types of ions, the pKas of the anions, or the free energies of electron transfer. In contrast to the earlier study of cleavage to carbanions and carbenium ions, the present ΔHhet values are predicted well by a general equation that employs the pKR+ of the carbenium ion (without modification) and the pKa of the phenol. The improvement is consistent with the fact that the cleavage of carbon-oxygen bonds of the triarylcarbinols used to establish the pKR+ stability scale is a more appropriate model for the heterolysis of carbon-oxygen bonds in sulfolane at 25°C than it is for the cleavage of carbon-carbon bonds under the same conditions.
Mechanism of reduction of trityl halides by lithium dialkylamide bases
Newcomb, Martin,Varick, Thomas R.,Goh, Swee-Hock
, p. 5186 - 5193 (2007/10/02)
Trityl chloride (TCl) and bromide are reduced by hindered lithium dialkylamide bases in THF to give predominantly triphenylmethane and a small amount of trityl dimer. Rate constants for the reduction of TCl by lithium diisopropylamide and lithium tert-butylethylamide in THF at -78 ?C have been measured; the reactions are first order in monomeric base and in trityl chloride. Inter- and intramolecular kinetic isotope effect studies employing β-deuterium substituted bases and substituent effect studies coupled with other kinetic information were used to formulate a scheme for the reactions. The reactions proceed by a rapid predissociation of the trityl halide to form an ion pair containing the trityl-THF oxonium cation followed by diffusion controlled electron transfer (ET) from the monomeric form of the base to the trityl-THF oxonium ion. The radical pair thus formed reacts by fast, highly regioselective β-hydrogen atom transfer from the aminyl radical to the methine carbon of the trityl radical to give triphenylmethane. Radical escape from the cage is a minor competing process. An outer-sphere ET process is energetically acceptable, but an inner-sphere process appears to be more likely.
Kinetic method for the measurement of the pKR value of the triphenylmethyl cation in the aqueous standard state
Mathivanan,McClelland, Robert A.,Steenken, Steen
, p. 8454 - 8457 (2007/10/02)
A kinetic method is presented for the measurement directly in the aqueous standard state of the equilibrium constant KR for the reaction Ph3C+ + H2O = Ph3COH + H+. The basis of the procedure is direct measurement of the rate constant kf for the reaction proceeding in the forward direction with the technique of laser flash photolysis. The rate constant kr for the reverse reaction is measured by following oxygen exchange in a labeled alcohol in a weakly acidic (0.005 M HCl) solution. At 25 °C in water, kf = (1.68 ± 0.06) × 105 s-1, kr = (5.79 ± 0.29) × 10-2 M-1 s-1, and the value for pKR calculated from their ratio is -6.46 ± 0.03. The value for kr is based on a slight extrapolation from 5% acetonitrile in water. The value for kf is measured in water. This directly measured value for pKR provides a test of the validity of the acidity function and excess acidity methods commonly employed to determine pK values for weak bases where the equilibrium with the conjugate acid form can only be studied in strong acids. Values of pKR previously reported for Ph3C+ based upon these approaches vary from -5.85 to -6.89, although the range is smaller, -6.44 to -6.89, if data obtained in concentrated HCl are omitted. The conclusion is that these methods do lead to pKR values in reasonable agreement with the directly measured number.
