Intermolecular acyl exchange in 1-acyloxypyridinium salts

Титов, Е. В.; Makarova, R. A.; Рыбаченко, В. И.; Chotii, K. Yu.; Goncharova, L. D.

doi:10.1007/bf00531202

Cited by 3 publications

(5 citation statements)

References 7 publications

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“…It was noticed in [39] that the conductivity isotherms of the salts R-C 5 H 4 N + -OAc Xalso indicate the presence of ion triplets with K 3 = (2.6-6.7)·10 −3 mol/l in solutions in CH 2 Cl 2 .…”

Section: Ion Triplets In Heteroarenium Saltsmentioning

confidence: 98%

“…In methylene chloride the dissociation of the salts 4-R-C 5 H 4 N + -OCOMeX − is very small, and with R = NMe 2 and X = Cl, Br, BPh 4 K d = (3.49, 4.78, 57.6)·10 −6 mol/l (according to Walden and Izmailov) [39]; the authors assume that the dependence of the dissociation constants on the nature of the substituents may be due to their effect on the distribution of charge in the cation of the ion pair.…”

Section: Salts Containing Aromatic Cations (Without Heteroatoms In Thmentioning

confidence: 99%

“…Symmetrical acyl exchange reactions in 1-acyloxypyridinium salts and pyridine N-oxides in solutions in methylene chloride were studied [39]: RC 5 H 4 N + OAc X -+ R-C 5 H 4 N*→O ⇄ RC 5 H 4 N→O + RC 5 H 4 N*OAc XThey take place by a mechanism of bimolecular nucleophilic substitution, and their rate is determined by the ionic forms of the reacting heterocyclic particles in the solution [39]. In methylene chloride solutions the salts are present mostly in the form of intimate ion pairs, the dissociation of which into ions is insignificant, and the kinetic parameters mainly characterize the reactivity of these particles, while the other particles do not have an effect.…”

Section: The Reactivity Of the Ions And Ionic Associates Of Heteroarementioning

confidence: 99%

“…For the 1-acetoxypyridinium salts 4-R-C 5 H 4 N + -OCOMe·X − (R = H, NMe 2 , OMe, X = Cl, Br, ClO 4 , BPh 4 ) [39,40], as also for the phenylacetyl analogs 4-R-C 5 H 4 N + -OCOCH 2 Ph·ClO 4 − (R = NMe 2 , OMe, H), the dissociation constants in acetonitrile (T = 298K) in the range of K d = (0.5-4.2)·10 −2 mol/l (calculated by the Shidlovskii method) were obtained [41], but the value of K d = 12.0·10 −2 mol/l in the last series with R = H falls outside the general series for no obvious reason.…”

Section: Salts Containing Aromatic Cations (Without Heteroatoms In Thmentioning

confidence: 99%

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Structure and characteristics of the ionic forms of heteroarenium salts in organic solvents (review)

Shvaika

Kovach

2009

Chem Heterocycl Comp

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The results of investigations into the formation of the various ionic forms of heteroarenium salts, their characteristics, and their reactivity are summarized. Salts containing (4n+2)π-electron aromatic cations (n = 0-3), including chalcogenopyrylium (O, S, Se), azinium, benzo-and dibenzoazinium, and chalcogenoazolium (O, S, Se, NR) ions are examined. In this system of compounds the relationships between the structure and the macroscopic characteristics of the heteroarenium salts (ionization constants, association/dissociation constants, distances of closest interionic approach) and the effect of the nature of the ionic forms in the solutions on their reactivity in heterolytic reactions are analyzed.Salt forms and in particular heteroarenium salts occupy an extremely important position in the chemistry of heterocyclic compounds, being of interest both in structural respects and in their high reactivity in nucleophilic reactions, recyclization reactions [1-3], and more recently at the applied level as ionic liquids [4]. It is on the basis of heteroarenium salts that the modern chemistry of stable carbenes -the organic chemistry of the divalent carbon atom -has developed [5][6][7][8][9].In spite of numerous investigations into the structure of the salts, carried out by various physicochemical methods (spectral, polarographic, X-ray crystallographic, etc.) direct information about their properties as salts, i.e., their capacity for dissociation/association and the formation of various ionic forms (free ions, various ionic associates -ion pairs and ion triplets), has remained almost in the dark. Among the characteristics directly describing the state of heteroarenium salts in solutions the most important are clearly the thermodynamic characteristics (which can be regarded as macroscopic in contrast to the microscopic characteristics relating, for example, to the spectral characteristics) -the ionic association (K a )/dissociation (K d ) constants, the distance of closest approach of the ions, and theories about the dependence of these quantities on the structure of the salts. Information on the ionic association of heteroarenium salts is of considerable interest for assessing their reactivity. It is also important for understanding the processes that give rise to the effectiveness of organic electrolytes containing heteroaromatic cations in physical systems (e.g., as luminophores [10]).

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Section: Ion Triplets In Heteroarenium Saltsmentioning

confidence: 98%

Section: Salts Containing Aromatic Cations (Without Heteroatoms In Thmentioning

confidence: 99%

Section: The Reactivity Of the Ions And Ionic Associates Of Heteroarementioning

confidence: 99%

Section: Salts Containing Aromatic Cations (Without Heteroatoms In Thmentioning

confidence: 99%

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Structure and characteristics of the ionic forms of heteroarenium salts in organic solvents (review)

Shvaika

Kovach

2009

Chem Heterocycl Comp

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“…Therefore, k rev values were not used in assessing the rate of the reverse reaction. The concentration of acylonium salts in acetonitrile in the kinetic experiments with IR monitoring was up to 10 !2 M and in the other cases it was not higher then 5 0 10 !3 M. Previously we showed [3] that under these conditions the dissociation degree of ionic dissociation of acylonium tetrafluoroborates in acetonitrile is close to one. The plots constructed by Eq.…”

mentioning

confidence: 89%

Rate and equilibrium constants of transfer of the dimethylcarbamoyl group between substituted pyridines and their N-oxides

et al. 2004

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Transfer of the dimethylcarbamoyl group from N-acyloxypyridinium salts to pyridines and from N-acylpyridinium salts to pyridine N-oxides was studied in acetonitrile. Equations relating the reaction rates and equilibria in the N3O and O3N acyl transfer series to the basicity of the nucleophile and leaving group were obtained. The reactions all are one-stage and occur by the forced concerted SN2 mechanism. The intersecting state model was used to obtain a modified Marcus equation that accounts for the asymmetry of the transition state with respect to reagents and products and allows uncontradictory analysis of the reaction mechanism.Previously we obtained kinetic and equilbrium data for reaction (1) of transfer of the dimethylcarbamoyl group from N-acylpyridinium salts to pyridines [1] and from N-acyloxypyridinium salts to pyridine N-The reaction mechanism was found out, and the reaction rate and equilibrium constants in these symmetrical reaction series were shown to adhere the Brønsted relation with b 0.5. At the same time, we found that the quality of reactivity predictions is much higher provided characteristics of identical reaction and the Marcus equation are used [2].In the present work we turned to unsymmetrical reactions (1) in which the carbamoyl group is transferred from N-acylpyridinium salts to peridine Noxides and, vice versa, from N-acyloxypyridinium salts to pyridine and substituted pyridines.In CH 3 CN we studied reactions of acylonium salts with nucleophiles (X = BPh 4 and Nu i , Nu j = Nu 1 3 Nu 20 ).The rate and equilibrium constants of reaction (1) in acetonitrile at 298 K are given in the table. The progress of reactions nos. 135,8,9, 14317, 20323, 36, 38, 40, and 53 was followed by UV spectroscopy at an optimal wavelength under pseudo-first-order reaction conditions at a tenfold or greater excess excess of acylonium salt or nucleophile. Reactions (41)3(44) were studied in a similar way by Fourier transform IR spectroscopy (FT-IR), following the decrease or increase of the intensity of absorption of acylonium salts in reactants and products, respectively.The corresponding n C=O values were as follows, cm !1 : 1797 (i = 5), 1789 (i = 6) 1787 (i = 7), and 1738 (i = 12). The rates of fast reactions nos. 6, 7, 18, 19, 24, 25, 31, 32, and 47352 were measured by the stoppedflow method. The second-order rate constants k 2 were calculated by Eq. (2) relating the apparent rate constants k ap (336 values) to the concentration of excess reagent by the least-squares method (k rev is the rate constant of the reverse reaction).(2) Treatment of kinetic data by Eq.(2) showed that k 2 >> k rev , whereas k rev~0 . Therefore, k rev values were not used in assessing the rate of the reverse reaction. The concentration of acylonium salts in acetonitrile in the kinetic experiments with IR monitoring was up to 10 !2 M and in the other cases it was not higher then 5 0 10 !3 M. Previously we showed [3] that under these conditions the dissociation degree of ionic dissociation of acylonium tetrafluoroborates in aceton...

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Theory of molecular bound states including Σ–Π vibronic interaction

Poluyanov

Schinke²

2003

Chemical Physics

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Intermolecular acyl exchange in 1-acyloxypyridinium salts

Cited by 3 publications

References 7 publications

Structure and characteristics of the ionic forms of heteroarenium salts in organic solvents (review)

Structure and characteristics of the ionic forms of heteroarenium salts in organic solvents (review)

Rate and equilibrium constants of transfer of the dimethylcarbamoyl group between substituted pyridines and their N-oxides

Theory of molecular bound states including Σ–Π vibronic interaction

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