The mechanism of deamination of methoxy substituted tritylammonium ions in methanolic aqueous acid

Bleasdale, Christine; Golding, Bernard T.; Lee, Won Heui; Maskill, Howard; Riseborough, Jane; Smits, Elly

doi:10.1039/c39940000093

Cited by 15 publications

(22 citation statements)

References 5 publications

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“…[5] now leads to eqs. [11] and [12] as the relationships for k f and k r in terms of the elementary rate constants in the mechanism of Scheme 1.…”

Section: Discussionmentioning

confidence: 99%

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The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Crugeiras¹,

Maskill²

1999

Can. J. Chem.

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We have studied the equilibration shown in eq. [3] of 4,4′-dimethoxytrityl alcohol in aqueous perchloric and nitric acids containing low proportions of acetonitrile using stopped-flow kinetics techniques. The rate constants for the overall progress to equilibrium, k obs , have been resolved into forward and reverse components using the equilibrium UV absorbance and a value for the molar absorptivity of the 4,4′-dimethoxytrityl carbenium ion determined in concentrated aqueous perchloric acid. The forward reaction (rate constant k f ) is first order in both the alcohol and the acid concentrations; the reverse reaction (rate constant k r ) is pseudo first order with respect to the carbocation. At constant hydronium ion concentration, the forward rate constant increases linearly with the concentration of electrolyte, whereas the reverse rate constant decreases. These effects depend upon the nature of the anion, but not the cation, and are not ionic strength effects. At constant anion concentrations, k f in both acids, and k r in perchloric acid, are independent of hydronium ion concentration; however, k r decreases with increasing hydronium ion concentration at constant nitrate concentration. At nonconstant ionic strength, changes in k f and k r observed in increasing concentrations of perchloric acid are attributable wholly to changes in perchlorate concentration. A mechanism is proposed which involves pre-equilibrium protonation of the alcohol, heterolysis of the protonated alcohol to give a 4,4′-dimethoxytrityl carbenium ion -water ion-molecule pair, then conversion of this into a dissociated carbenium ion in equilibrium with ion pairs. To account for the strong effects of perchlorate and nitrate upon the forward rate constants, it is proposed that these anions provide additional reaction channels from the ion-molecule pair. However, we find no evidence of acid catalysis in the reaction of the ion-molecule pair (in contrast to our finding for the reaction of the corresponding ion-molecule pair formed from dimethoxytritylamine in acidic media). Some of the elementary rate and equilibrium constants of the proposed mechanism have been evaluated.

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“…[5] now leads to eqs. [11] and [12] as the relationships for k f and k r in terms of the elementary rate constants in the mechanism of Scheme 1.…”

Section: Discussionmentioning

confidence: 99%

“…Electrolyte solutions were made from the commercial products of the highest purity available (Merck). 4,4′-Dimethoxytrityl alcohol was available from previous studies at Newcastle (10,11).…”

Section: Reagentsmentioning

confidence: 99%

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Crugeiras¹,

Maskill²

1999

Can. J. Chem.

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“…[1] We have reported previously that (substituted) tritylamines under acidic conditions, where they are present as the corresponding (substituted) tritylammonium cations, undergo deamination reactions, and that these are specific acid catalysed. [2,3] This was an exceptional finding as the tritylammonium cation has no basic site at the reaction centre to accept a proton, and a mechanism involving intermediate ion-molecule pairs was proposed. Methoxy substituents at the para positions of the phenyl groups are, as expected, rate enhancing, and these rate effects are observed in both the catalysed and uncatalysed reaction channels.…”

Section: Introductionmentioning

confidence: 98%

“…For 1h, ∆H ᮎ = 40. 2 Bn) (3d; 886.6) have been determined by ICR measurements. The GB of TrNHAc corresponds to protonation at oxygen and B3LYP/6-31G* calculations indicate that the N-protonated isomer is 46.4 kJ·mol −1 less stable, i.e.…”

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confidence: 99%

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Base Strengths of Substituted Tritylamines, N‐Alkylanilines, and Tribenzylamine in Aqueous Solution and the Gas Phase: Steric Effects Upon Solvation and Resonance Interactions

et al. 2004

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Ring‐chain interconversion of sulforhodamine‐amine conjugates involves an unusually labile CN bond and allows measurement of sulfonamide ionization kinetics

Corrie¹,

Eccleston²,

Ferenczi³

et al. 2008

J of Physical Organic Chem

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AbstractpH‐dependent interconversion between ring and chain forms of sultams/sulfonamides derived from conjugates of sulforhodamines with amines, and the associated sulfonamide ionization, have been studied by a combination of equilibrium and kinetic methods. The colorless, ring‐closed sultam form is favored at alkaline pH with an apparent pKa of 7.37 for the color change of the methylamine conjugate of Sulforhodamine B. The ring‐closed form is also favored at very low pH (apparent pKa ∼ 0.68) by protonation of both diethylamino substituents. The kinetics of interconversion between open and closed forms were measured at 4°C over the pH range 0–13. The observed rate constant ranges over nine orders of magnitude from 4.8 × 10−4 s−1 at pH 1 to 2.27 × 106 s−1 at pH ≥ 12. Above pH 2, the data are accommodated by a mechanism that includes cleavage of the sultam CN bond in the ring opening step with a sulfonamide anion as the leaving group, and in the reverse reaction, OH−‐dependent ionization of the sulfonamide at 4.8 (±2.0) × 109 M−1 s−1. Below pH 2, H+‐dependent protonation occurs at 1.4 (±0.4) × 10−3 M−1 s−1. X‐ray crystallography of a related N‐methylsultam showed that the labile, endocyclic CN bond is significantly longer than the exocyclic NCH3 bond (1.509 Å and 1.445 Å, respectively). Laser‐induced ring opening of the closed form has potential application as an orientation probe of biological macromolecules. Copyright © 2008 John Wiley & Sons, Ltd.

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The mechanism of deamination of methoxy substituted tritylammonium ions in methanolic aqueous acid

Cited by 15 publications

References 5 publications

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

The 4,4'-dimethoxytrityl carbenium ion by ionization of 4,4'-dimethoxytrityl alcohol in acetonitrile - aqueous perchloric and nitric acids containing electrolytes: kinetics, equilibria, and ion-pair formation

Base Strengths of Substituted Tritylamines, N‐Alkylanilines, and Tribenzylamine in Aqueous Solution and the Gas Phase: Steric Effects Upon Solvation and Resonance Interactions

Ring‐chain interconversion of sulforhodamine‐amine conjugates involves an unusually labile CN bond and allows measurement of sulfonamide ionization kinetics

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