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• 34073-78-4 4-dimethylamino-4'-methoxytriphenylmethyl cation 

Relevant academic research and scientific papers

Stabilities of trityl-protected substrates: The wide mechanistic spectrum of trityl ester hydrolyses

Ionization rates of para-substituted triphenylmethyl (trityl) acetates, benzoates, and para-nitrobenzoates have been determined in aqueous acetonitrile and aqueous acetone at 25 °C. Conventional and stoppedflow techniques have been used to evaluate rate constants ranging from 1.38 × 10-5 to 2.15 × 102S-1 by conductimetry and photospectrometry methods. The varying stabilities of the differently substituted tritylium ions account for a gradual change of reaction mechanism. Poorly stabilized carbocations are generated slowly by the ionization of their covalent precursors and trapped fast by water. Better stabilized carbocations are generated more rapidly and accumulate, so that ionization and trapping by water can be observed as separate steps in a single experiment. Finally, highly stabilized tritylium ions do not react with water, and only the rates of their formation could be measured. The ionization rate constants correlate linearly with Winstein's ionizing powers Y; the low slopes (0.17 + parameters is excellent for symmetrically substituted tritylium derivatives, deviations for unsymmetrically substituted systems are observed. The failing rate-equilibrium relationship between the rates of ionizations (log kion) and the stabilities of the carbocations in aqueous solution (pKR+) may be explained by the late " development of resonance between a p-amino group and the carbocationic center of the tritylium ion during the ionization process.

Electrophilicity versus electrofugality of tritylium ions in aqueous acetonitrile

First-order rate constants kw for the reactions of a series of donorsubstituted triphenylmethylium (tritylium) ions with water in aqueous acetonitrile have been determined photometrically at 20°C using stopped-flow and laser-flash techniques. T

Base-Catalyzed Reactions of Triarylmethyl Carbocations with Water

The general base catalyzed addition of water to a series of triarylmethyl carbocations has been studied in aqueous solution with a series of substituted quinuclidines as base catalysts.Broensted β values for general base catalysis range from 0.33 for trianisylmethyl carbocation, TAM (pKR(1+)=0.82), to 0.52 for Malachite Green, MG (pKR(1+)=6.94).There is a slight tendency for the β values to decrease with decreasing carbocation stability.The rate constants for the "water"-catalyzed reactions show a large positive deviation (800-fold in the case of Malachite Green) and the rate constants for the hydroxide ion catalyzed reactions a small negative deviation from Broensted plots based on quinuclidine catalysis.These results are consistent with a concerted mechanism for the buffer-catalyzed reactions, a stepwise mechanism that proceeds through an oxonium ion intermediate for the "water"-catalyzed reactions (this mechanism corresponds to an A-1 mechanism in the microscopic reverse direction), and either a concerted or preassociation mechanism for the hydroxide ion catalyzed reactions.The positive deviation of water and the negative deviation of the hydroxide ion from the Broensted relationship are opposite the deviations that are normally observed for these species in related reactions: compared to these related reactions, the pH range where buffer catalysis is strongest is shifted to higher pH values.These results also explain why the early attempts to find general base catalysis of the addition of water to triarylmethyl carbocations with acetate buffers proved unsuccessful.

EFFECT OF STRUCTURAL FACTORS ON THE KINETICS OF THE FORMATION OF DERIVATIVES OF 4-DIMETHYLAMINO-4'-METHOXYTRIPHENYLCARBINOL

The kinetics of the alkaline hydrolysis of a series of subtituted 4-dimethylamino-4'-methoxytriphenylcarbonium ions in water were studied by a spectrophotometric method.The activation parameters of the process were determined.Within the limits of the investigated reaction series there are two isokinetic temperatures, i.e., for donor and acceptor substituents, and accordingly various types of reactivity control.As a result of this the Hammett plots contain an inflection, the degree of which decreases with increase in temperature.The reactivity of the investigated cations with respect to water is practically independent of the substituent.

APPLICABILITY OF ELECTROSTATIC THEORY TO THE KINETICS OF THE FORMATION OF AMINOTRIARYLCARBINOLS

By analysis of the results obtained during spectrophotometric investigation of the kinetics of the formation of aminotriarylcarbinols in the water-acetone mixed solvents it was shown to be possible to use electrostatic theory for quantitative estimation of the contribution from the effect of the mixed solvent to the kinetic parameters of the reaction.