Molar absorptivity and pK<sub>R+</sub>of the 4,4′-dimethoxytrityl carbenium ion in methanolic water, and its equilibrium with chloride ion

Lee, Won Heui; Maskill, Howard

doi:10.1039/p29940001463

Cited by 5 publications

(7 citation statements)

References 14 publications

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“…The higher basicity of amines compared with alcohols, and the greater ease of C–N bond breaking relative to the C–O bond, suggested that tritylamines should readily undergo reactions similar to those of the alcohols and ethers . Although tritylamines, in contrast to alcohols, are wholly protonated in dilute aqueous strong acid, detailed studies showed that ion–molecule pairs are involved in these reactions, which turned out to be general for tritylamines and N‐tritylhydroxylamines .…”

Section: Introductionmentioning

confidence: 64%

“…The equilibrium constants

K_{R^{+}}

for the hydration of the carbenium ion (Eqn ) were obtained from absorbance measurements for the different carbenium ions

{normalR}^{+} + 2 H_{2} O \overset{K_{{normalR}^{+}}}{⇌} {ROH + H}_{3} {normalO}^{+}

…”

Section: Resultsmentioning

confidence: 99%

“…The higher basicity of amines compared with alcohols, and the greater ease of C-N bond breaking relative to the C-O bond, [11] suggested that tritylamines should readily undergo reactions similar to those of the alcohols and ethers. [12,13] Although tritylamines, in contrast to alcohols, are wholly protonated in dilute aqueous strong acid, detailed studies showed that ion-molecule pairs are involved in these reactions, which turned out to be general for tritylamines [14][15][16][17] and Ntritylhydroxylamines. [18] In all reactions investigated in this study, the final product is an equilibrium mixture of substituted trityl carbenium ion and solvolysis product (overwhelmingly the trityl alcohol) as determined by the composition of the solvent and relevant equilibrium constants, e.g.…”

Section: Introductionmentioning

confidence: 99%

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Acid‐catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media

Canle

Maskill

2013

J of Physical Organic Chem

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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 À3 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 3 O + ] = 0. Strong upward curvature has been observed for k obs versus [HClO 4 ]. Analysis of this dependence in terms of the H R acidity function and the X 0 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

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Section: Introductionmentioning

confidence: 64%

“…The equilibrium constants

K_{R^{+}}

for the hydration of the carbenium ion (Eqn ) were obtained from absorbance measurements for the different carbenium ions

{normalR}^{+} + 2 H_{2} O \overset{K_{{normalR}^{+}}}{⇌} {ROH + H}_{3} {normalO}^{+}

…”

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Acid‐catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media

Canle

Maskill

2013

J of Physical Organic Chem

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“…the pK R ϩ of the particular carbocation), in addition to the initial concentration of the substrate and the acidity of the medium. 13 In a representative case, we established that the final equilibrium under the same experimental conditions was the same starting from equal concentrations of the trityl alcohol and the tritylamine (although the former reacted much faster).…”

Section: Methods and Resultsmentioning

confidence: 85%

Substituent effects upon rates of deamination and base strengths of substituted N-tritylamines

Canle

Demirtaş

Maskill

2001

J. Chem. Soc., Perkin Trans. 2

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Substituted N-tritylamines undergo deamination in aqueous acidic solution containing organic cosolvents, and follow a pseudo first-order specific acid-catalysis rate law (k obs = k 0 ϩ k H [H 3 O ϩ ]); the products are the corresponding trityl alcohols in equilibrium with the trityl carbenium ions, and ammonium ions. The change from 4,4Ј-dimethoxyto 4,4Ј,4Љ-trimethoxy-tritylamine increases reactivity by a factor of about 30 in both k 0 and k H , but N-alkyl and Naryl groups have much greater effects (ca. 10 6 for both k 0 and k H for 4,4Ј-dimethoxytritylamine) which are largely independent of the nature of the N-alkyl and N-aryl groups. The anions of the catalytic strong acids (perchlorate, chloride, bromide, and nitrate) have only small effects as also does the concentration of acetonitrile as cosolvent; ethanoic acid as cosolvent is mildly rate-enhancing. Substituents in the aniline residue of N-(4,4Ј-dimethoxytrityl)anilines have virtually no effect upon either k 0 or k H (ρ = 0 for both). The results are interpreted by a mechanism involving a pre-equilibrium heterolysis of the (substituted) tritylammonium ion to give an ion-molecule pair which may undergo diffusional or acid-catalysed dissociation before the (substituted) trityl cation undergoes equilibrium nucleophilic capture by water. Base strengths of some substituted N-tritylamines have been measured; the substituted N-trityl group causes all amines (aliphatic and aromatic) to be comparably strongly basic (pK BH ϩ ca. 9).

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“…As the product decomposed on silica and alumina, it was isolated by crystallisation from ether-petrol in the refrigerator for 48 h as orange crystals (80 mg, 44%, mp 139-140 ЊC; δ H : 1.60 (1H, br, OH), 3.87 (9H, s, OCH 3 ), 6.94 (6H, d, J 8.9, H-3,3Ј,3Љ,5,5Ј,5Љ), 7.77 (6H, d, J 8.9, H-2,2Ј,2Љ,6,6Ј,6Љ); δ C : 55. 21…”

Section: N-(44ј4љ-trimethoxytrityl)hydroxylamine (4a)mentioning

confidence: 99%

N-Tritylhydroxylamines: preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

Canle

Clegg

Demirtaş

et al. 2001

J. Chem. Soc., Perkin Trans. 2

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Molar absorptivity and pK_R+of the 4,4′-dimethoxytrityl carbenium ion in methanolic water, and its equilibrium with chloride ion

Cited by 5 publications

References 14 publications

Acid‐catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media

Acid‐catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media

Substituent effects upon rates of deamination and base strengths of substituted N-tritylamines

N-Tritylhydroxylamines: preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

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Molar absorptivity and pKR+of the 4,4′-dimethoxytrityl carbenium ion in methanolic water, and its equilibrium with chloride ion

Cited by 5 publications

References 14 publications

Acid‐catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media

Acid‐catalysed hydrolysis of trityl derivatives in strongly acidic aqueous media

Substituent effects upon rates of deamination and base strengths of substituted N-tritylamines

N-Tritylhydroxylamines: preparations, structures, base strengths, and reactions with nitrous acid and perchloric acid

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Product

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Molar absorptivity and pK_R+of the 4,4′-dimethoxytrityl carbenium ion in methanolic water, and its equilibrium with chloride ion