80054-70-2Relevant academic research and scientific papers
A Self-Assembled Cage with Endohedral Acid Groups both Catalyzes Substitution Reactions and Controls Their Molecularity
Bogie, Paul M.,Holloway, Lauren R.,Ngai, Courtney,Miller, Tabitha F.,Grewal, Divine K.,Hooley, Richard J.
supporting information, p. 10232 - 10238 (2019/07/09)
A self-assembled Fe4L6 cage complex internally decorated with acid functions is capable of accelerating the thioetherification of activated alcohols, ethers and amines by up to 1000-fold. No product inhibition is seen, and effective
Acid-catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media
Canle L., Moises,Maskill, Howard
, p. 1016 - 1022 (2014/01/06)
The kinetics of hydrolysis (deamination or dealcoholation) of tritylamines and 2,2,2-trifluoroethyl ethers and their corresponding 4-methoxy, 4,4′-dimethoxy-, and 4,4′,4″-trimethoxy-substituted analogues in aqueous solutions up to 3.5 mol · dm-3 in strong acid have been investigated at constant ionic strength. In all cases, acid-catalysed hydrolytic processes have been observed, with finite reactivity at [H 3O+] = 0. Strong upward curvature has been observed for kobs versus [HClO4]. Analysis of this dependence in terms of the HR acidity function and the X0 excess acidity scale allow explanation of the observed behaviour in terms of the increasing differences between concentrations and activities of the various species involved in the processes, including water, for which the activity coefficient strongly diverges from its standard state value as the acidity increases. This analysis has shown that, by taking account of the effect of the ionic strength, the same mechanistic models proposed for mildly acidic solutions are valid in more highly concentrated acid media. These comprise (i) protonation of the trityl ether followed by C-O bond heterolysis to give a carbenium ion-alcohol (ion-molecule) pair which can separate, and (ii) C-N bond heterolysis of the protonated tritylamine to give a carbenium ion-amine (ion-molecule) pair followed by separation of the fragments or protonation of the amine and subsequent separation of the ions. Each separated (substituted) trityl carbenium ion, regardless of its provenance, is invariably captured by a solvent molecule (water). Copyright 2013 John Wiley & Sons, Ltd. Strong upward curvatures observed for kobs versus [H3O+] kinetics results in the hydrolysis of tritylamines and trityl ethers in strongly acidic aqueous solutions are entirely understandable as medium effects and accurately described in terms of excess acidities. The mechanisms previously proposed for mild acidic conditions have been generalized to more strong acid media. Copyright
Acid-catalysed hydrolysis of methoxy-substituted trityl trifluoroethyl ethers: A kinetic and computational investigation of leaving group effects
Lopez, Moises Canle,Demirtas, Ibrahim,Maskill, Howard,Mishima, Masaaki
experimental part, p. 614 - 621 (2009/04/04)
Trityl trifluoroethyl (TFE) ether and its 4-methoxy, 4,4′-dimethoxy-, and 4,4′,4″-trimethoxy-substituted analogues have been prepared; the dimethoxy and trimethoxy compounds undergo ready acid-catalysed hydrolysis at constant ionic strength = 1 mol dm-3 at 25°C. The monomethoxy compound is less reactive and the parent trityl analogue showed minimal reactivity. Using presently reported and literature kinetics results with pKa values of protonated substrates, first-order rate constants covering 12 orders of magnitude have been determined for heterolysis/ dissociation of 11 protonated dimethoxytrityl derivatives DMTrYH+ where YH = H2O, CF3CH2OH, ArNH2 and RNH2. There is a good correlation between logarithms of these rate constants and the pKa values of the conjugate acids (YH 2+) of the nucleofuges YH. Enthalpies and corresponding free energies at 25°C for the dissociation of the specifically solvated ions CH3 - YH(H2O)n+ (YH = MeOH and CF3CH2OH, n = 1; H2O, n = 2; and NH 3, n = 3) have been calculated at the B3LYP/6-31+G* level. Corresponding gas phase calculations have also been carried out for Ph 3C YH(H2O)n+ (YH = H2O, n = 2; MeOH, n = 1; CF3CH2OH, n = 1 and NH3, n = 3) and, in addition, structures for these solvated ions with (YH = H 2O, MeOH and NH3) have been calculated. The specifically solvated ion Ph3C - O(H)CH2CF3(H 2O)+ does not correspond to a stable bonded species in the gas phase, which suggests that acid-catalysed fragmentation of methoxy-substituted analogues of Ph3C - OCH2CF3 in aqueous solution are concerted with proton transfer in which case the hydrolytic cleavage will be general acid catalysed. Copyright
Electrophilic Reactivity of the Triphenylmethyl Carbocation in Aqueous Solutions
McClelland, Robert A.,Banait, Narinder,Steenken, Steen
, p. 7023 - 7027 (2007/10/02)
The triphenylmethyl (trityl) carbocation has been generated as a transient intermediate by laser flash photolysis of 1:2 (v/v) acetonitrile:water solutions of trityl acetate and trityl 4-cyanophenyl ether.Identification of the transient as the free carbocation in the ground state was based on its characteristic absorption spectrum and upon conductivity changes.Rate constants have been measured for the reaction of the cation in this solvent with a series of ionic and neutral nucleophiles.The solvent rate constant at 20 deg C is 1.5 x 105 s-1.Azide ions reacts at 4.1 x 109 M-1s-1; the directly measured azide:water ratio is compared to literature values determined by product analysis.Chloride ion reacts at 2 x 106 M-1 s-1; with bromide the equilibrium addition can be observed with k(comb) = 5 x 106 M-1 s-1 and k(ion) for Ph3CBr = 8 x 105 s-1.Rate constants do not adhere to the N+ relationship.This predicts a slope of unity in a plot of log k(Ph3C+) vs.N+, with the better nucleophiles reacting at the 1010 encounter-controlled limit.Azide is the only nucleophile of those studied to approach this.Sulfite and thiolate ions, which are better N+ nucleophiles, react at 2-3 x 108 M-1s-1, while amines react in the 106-107 M-1s-1 range.The plot vs.N+ has a slope of 0.3-0.4.One explanation is that rate constants for the better nucleophiles do level, but this occurs considerably below the 1010 limit.Alternatively, the less than unit slope is real and this more reactive cation, in contrast to more stable analogues, is exhibiting selectivity.
