Protonation of (dimethyl) amino and methoxyl groups in oxonium and carbonium ions. Electronic spectra

Sekuur, Th.J.; Kranenburg, P.

doi:10.1016/0584-8539(73)80048-0

Cited by 6 publications

(8 citation statements)

References 6 publications

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“…If AMPSA is present in excess, further changes in chemical shifts occur and can be interpreted as the occurrence of diprotonation together with hydrogen-bonding interactions. This view is in accordance with literature data. − and in particular with studies carried out in toluene/trifluoroacetic acid media . The interaction of MK and AMPSA has to be looked at as a multistage equilibrium involving protonation and hydrogen bonding at the same time.…”

Section: Resultssupporting

confidence: 93%

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Molecularly Imprinted Anisotropic Polymer Monoliths

1996

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Anisotropic materials with selective binding properties may have potential as active components in optical sensors. A novel route for the synthesis of such materials is described and the validity of the concept has been demonstrated. To this end free radical polymerization of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol trimethacrylate (TRIM) in the presence of a template molecule [4,4′-bis(dimethylamino)benzophenone (Michler's ketone)] and binding sites [2-(acrylamido)-2-methylpropanesulfonic acid (AMPSA) or methacrylic acid (MAA)] led to molecularly imprinted polymer monoliths. Upon irradiation using linearly polarized light, the template molecules reacted with the polymer networks to form transparent and anisotropic polymer monoliths. The origin of the dichroism is discussed and is believed to result from the incorporation of reactive template molecular species (radicals) into the polymer network. That the polymers are indeed imprinted was confirmed using competitive binding studies. The polymers are size and shape selective but not always in favor of the template molecule.

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Section: Resultssupporting

confidence: 93%

“…This view is in accordance with literature data. [31][32][33][34][35] and in particular with studies carried out in toluene/trifluoroacetic acid media. 32 The interaction of MK and AMPSA has to be looked at as a multistage equilibrium involving protonation and hydrogen bonding at the same time.…”

Section: Resultsmentioning

confidence: 99%

Molecularly Imprinted Anisotropic Polymer Monoliths

1996

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“…As mentioned, the two absorption maxima of 3 are attributed to two different chemical constitutions of 3 . The absorption maximum at about λ max ( 3 ) = 500 nm is caused by the oxenium ion of 3 , which is produced by selectively complexing the carbonyl oxygen of 3 with either a proton or a Lewis acid. , Consequently, Lewis and/or Brønsted acid sites on the surface can be responsible for the strong complexation of the carbonyl oxygen of 3 . To differentiate between the two options, surface titration of adsorbed 3 with pyridine and DTBP was carried out.…”

Section: Resultsmentioning

confidence: 99%

“…The solvatochromic UV/vis absorption band of 3 is attributed to a π−π* transition which overlaps with the less intense n−π* transition. , The solvatochromism of 3 has been investigated by several authors. ,, On increasing both the HBD capacity and dipolarity/polarizability of a solvent, the UV/vis absorption band of 3 undergoes a significant bathochromic shift. The bathochromic effect is even significantly enhanced when a strong Lewis acid or a mobile proton interacts additionally with the carbonyl oxygen atom of 3 because a mesomerically stabilized oxenium ion is generated. − In contrast, protonation of the nitrogen atoms of the dimethylamino groups by a Brønsted acid has a hypsochromic influence on the solvatochromic UV/vis absorption band of 3 . For instance, the UV/vis absorption band of [4-(CH 3 ) 2 NC 6 H 4 ] 2 CO−Si(CH 3 ) 3 + appears at λ = 505 nm 59 and of {[4-(CH 3 ) 2 NHC 6 H 4 ] 2 CO} 2+ at λ = 310 nm .…”

Section: Introductionmentioning

confidence: 99%

Probing the Surface Polarity of Various Silicas and Other Moderately Strong Solid Acids by Means of Different Genuine Solvatochromic Dyes

2000

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Reichardt's E T (30) as well as Kamlet-Taft's R (hydrogen-bond-donor acidity) and π* (dipolarity/polarizability) values of various solid acids, e.g., silicas, aluminas, alumosilicates, titanium dioxides, and aluminafunctionalized silica particles, are presented. The E T (30) values of the solid acids were directly measured by UV/vis spectroscopy using 2,6-diphenyl-4-(2,4,6-triphenyl-1-pyridinio)phenolate (1a) and an eicosafluorinesubstituted derivative of 1a (1b) as surface polarity indicators. Kamlet-Taft's R and π* parameters for the various solid acids are analyzed by means of Fe(phen) 2 (CN) 2 [cis-dicyano-bis(1,10-phenanthroline)iron(II)] (2) and Michler's ketone [4,4′-bis(N,N-dimethylamino)benzophenone] (3) as solvatochromic surface polarity indicators. The chemical interpretation of the R and π* parameters and the nature of the surface sites which they reflect are discussed. The correspondence of the UV/vis spectroscopic results to those of the IR-sensitive probe benzophenone and the fluorescence probe pyrene (literature data) is also discussed. It is evident that the solid surface environments observed by the various indicators are moderately strong dipolar/polarizable (π* ) 0.38 to 1.04) and are fairly strong hydrogen-bond donors (R ) 1.00 to 1.99). Theoretical E T (30) values of solid acids are calculated by applying linear solvation energy (LSE) relationships using the independently measured R and π* values of the solid acids according to E T ( 30) ) [E T (30)] o + aR + sπ*. The respective dependence of the R and π* terms, expressed by the coefficients a and s, upon the measured E T (30) value for solid acids is discussed in comparison to related multiple LSE correlations known for wellbehaved regular solvents and functionalized silicas. The results show in general that values of polarity parameters of strong HBD and dipolar surfaces are strongly influenced by the experimental conditions applied.

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“…The other one at about λ max (2) ≈ 500 nm is attributed to an oxycarbenium ion of 2, which is produced by selectively complexing the carbonyl oxygen of 2 either by a proton or Lewis acid. 36,37 In previous papers, 17,36a we have shown that one can distinguish between these two options by surface titration of adsorbed 2 with pyridine and 2,6-di-tertbutylpyridine, respectively, as competing bases. In principle, two values of the R and π* parameters of alumina and aluminosilicate can be determined using the two different λ max (2) values of adsorbed 2 in eqs 4 and 5.…”

Section: Resultsmentioning

confidence: 95%

Solvent Influence on the Catalytic Activity and Surface Polarity of Inorganic Solid Acids

and

Spange

2002

J. Phys. Chem. B

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The surface-mediated hydride-transfer reaction of 1,4-cyclohexadiene with triphenylmethylium induced by two silicas, an alumina, and an aluminosilicate as solid acid catalyst, respectively, has been kinetically studied as a function of the polarity of the surrounding solvent. The specific rate constants k′ have been determined in 10 different solvents. Generally, k′ decreases with increasing polarity of the solvent. Kamlet-Taft's R (hydrogen-bond acidity) and π* (dipolarity/polarizability) parameters of the solid acid/solvent interface have been determined for alumina and aluminosilicate in various solvents. Fe(phen) 2 (CN) 2 [cis-dicyanobis(1,10phenanthroline)iron(II), ( 1)] and Michler's ketone [4,4′-bis(N,N-dimethylamino)benzophenone, (2)] were used as solvatochromic surface polarity indicators. The UV/vis spectra of the two surface polarity indicators 1 and 2 adsorbed on solid acid catalysts from the solvents were measured by the reflection mode and the UV/vis absorption maxima were used to calculate the R and π* values of the catalysts. R of the solid acid catalyst/ solvent interface decreases with increasing β term (hydrogen-bond accepting) ability of the solvent, whereas the π* term of the solvent marginally modifies the interfacial polarity. k′ increases for each individual solvent with increasing β of the catalyst solvent interface in the order series silica < alumina < aluminosilicate. It can be shown that R of the solid acid catalyst/solvent interface decreases with increasing β term (hydrogenbond accepting) ability of the solvent, whereas the π* term of the solvent marginally modifies the interfacial polarity.

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Protonation of (dimethyl) amino and methoxyl groups in oxonium and carbonium ions. Electronic spectra

Cited by 6 publications

References 6 publications

Molecularly Imprinted Anisotropic Polymer Monoliths

Molecularly Imprinted Anisotropic Polymer Monoliths

Probing the Surface Polarity of Various Silicas and Other Moderately Strong Solid Acids by Means of Different Genuine Solvatochromic Dyes

Solvent Influence on the Catalytic Activity and Surface Polarity of Inorganic Solid Acids

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