Vladislav M. Vlasov

Comparison of brönsted acidities of neutral NH-acids in gas phase, dimethyl sulfoxide and water

Abstract The Bronsted acidities of several neutral NH-acids (substituted diphenylamine, substituted anilines and imides) were measured in the gas phase (pulsed FT ICR spectrometry), dimethyl sulfoxide and aqueous solution. Comparison of the Bronsted acidities of neutral NH-acids in the gas phase, dimethyl sulfoxide and water was also carried out. It was shown that substituent effects on the acidity of the studied compounds are significantly attenuated by the transfer of the reaction series of acidic dissociation of neutral acids from the gas phase into dimethyl sulfoxide and water. The strongest solvent-induced attenuation of the substituent effects is characteristic of the meta-substituted anilines whose sensitivity towards substituent effects decreases with transfer from the gas phase into DMSO by 2.83 times and with transfer into water by 4.13 times. At the same time, the reaction series of para and/or ortho-π-acceptor substituted anilines, amides, imides and substituted diphenylamines are less sensitive to a change in gas phase for DMSO or water. In the special case of para-acceptor substituted anilines it was demonstrated that the specific solvation induced an increase in the acidity of the para- and/or ortho-acceptor substituted anilines as compared with the behavior of the corresponding meta-substituted anilines by amounts up to 10 pKa units.

Kinetics of the reaction of 4-nitrophenyl benzoates with 4-chlorophenol in the presence of potassium carbonate in dimethylformamide

The effect of the substituent in the benzoyl group on the relative rate and activation parameters of transesterification of substituted 4-nitrophenyl benzoates with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate was studied by the competing reaction technique. The whole series of benzoates showed the enthalpy-entropy compensation effect. 4-Nitrophenyl benzoates having electronacceptor substituents give rise to isokinetic relationship with an isokinetic temperature β of 382 K. The mechanism of the transesterification process is discussed.

Activation parameters of the reactions of 4-nitrophenyl benzoates and S-phenyl benzothioate with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate

The kinetics of transesterification of 4-nitrophenyl benzoates and S-phenyl benzothioate with 4-chlorophenol in dimethylformamide in the presence of potassium carbonate were studied. Variation of the substrate reactivity and activation parameters of the process is discussed with respect to the substituent in the benzoic acid fragment.

Enthalpy and entropy relations in reactions of 2,4-dinitrophenyl benzoate with phenols in the presence of potassium carbonate in dimethylformamide

By means of competing reactions procedure the temperature dependence of the relative reactivity of phenols in reactions with 2,4-dinitrophenyl benzoate in the presence of potassium carbonate and DMF was examined. The correlation analysis of the relative rate constants kArOH/kPhOH and the difference in the activation parameters (ΔΔH≠ and ΔΔS≠) of the competeing reactions revealed the existence of three isokinetic series. The interpretation of the transesterification mechanism was performed applying the approach underlain by the analysis of the effect of substituents nature on the activation parameters.

Effects of substituents on activation parameters in the reactions of carboxylic acid derivatives with anionic and neutral nucleophiles

Changes of activation parameters, ΔH‡ and ΔS‡, with σ constants of substituents in the reactions of carboxylic acid derivatives with anionic and neutral nucleophiles in various solvents give the δΔH‡ and δΔS‡ reaction constants which are linearly related for variations of substituents in substrate and nucleophile. The dependences obtained, δΔH‡vs.δΔS‡, allow estimation of the contribution of changes of the internal enthalpy, δΔH‡int, to the enthalpy reaction constant, δΔH‡, which give a single linear dependence on the Hammett ρ reaction constants. The results obtained show that the substituent effects on the charge development in the transition state are governed by the magnitude of δΔH‡int.

Comparison of Brønsted acidities of neutral CH acids in gas phase and dimethyl sulfoxide

The Bronsted acidities of a number of neutral CH-acids (substituted toluenes, aryl- and diarylacetonitriles, fluorenes, ethyl esters of phenylcyanoacetic acids, substituted methanes, etc.) were measured in the gas phase (pulsed FT-ICR spectrometry) and in dimethyl sulfoxide (potentiometric titration). Comparison of the Bronsted acidities of the neutral CH-acids in the gas phase and in dimethyl sulfoxide (DMSO) was also carried out. It was shown that, as a rule, substituent effects on the acidity of the studied compounds are significantly attenuated by the transfer of the reaction series of acidic dissociation of neutral acids from the gas phase into DMSO. The weakest attenuation was monitored in the case of aromatic hydrocarbons, which are the conjugate acids of carbanions with very extensive charge delocalization (fluoradene, substituted fluorenes, aryl-substituted cyclopentadienes and indenes, toluene, diphenyl and triphenylmethanes, etc.). The strongest solvent-induced attenuation of the substituent effects is characteristic of meta-substituted phenylacetonitriles and phenylmalononitriles, whose sensitivity towards substituent effects decreases with transfer from the gas phase into DMSO by up to 2.8–3.3 times. At the same time, the reaction series of para and/or ortho-π-acceptor substituted phenylacetonitriles are less sensitive to a change from the gas phase to DMSO. In the series of α-cyanosubstituted toluenes the solvent attenuation of substitution effects in the benzene ring increases with the successive inclusion of cyano groups into the α-position. In the special case of para-acceptor substituted phenylacetonitriles it was demonstrated that the specific solvation induced an increase in the acidity of the para- and/or ortho-acceptor substituted phenylacetonitriles as compared to the behavior of the corresponding meta-substituted phenylacetonitriles by up to 3.6 pKa units.

Substituent effects on the activation parameters of SNar reactions

The reaction constants δΔH≠ and δΔS≠ derived from the dependences of the ΔH≠ and ΔS≠ activation parameters on substituent constants σ in SNAr reactions of substituted benzenes with anionic and neutral nucleophiles in various solvents were found to be linearly related upon variation of substituents in the substrate and nucleophile. The δΔH≠—δΔS≠ dependences make it possible to estimate the contribution of the internal enthalpy δΔH≠t into the enthalpy reaction constant δΔH≠. The δΔH≠int values are linearly related to the Hammett p values. Deviations from the linear dependence δΔH≠int—n were interpreted in terms of change of the reaction mechanism. Substituent effect on the development of charge in the transition state is determined by the δΔH≠int value.

Kinetics of the reaction of substituted 4-nitrophenyl benzoates with benzenethiol in the presence of potassium carbonate in dimethylformamide

The effect of the substituent nature on the rate and activation parameters of transesterification of a series of 4-nitrophenyl benzoates with benzenethiol in dimethylformamide in the presence of potassium carbonate was studied by the competing reaction method. In all cases, change of the Gibbs energy of activation is determined mainly by variation of the enthalpy of activation. 4-Nitrophenyl benzoates having electron-withdrawing substituents in the benzoyl fragment were found to fit an isokinetic relation with an isokinetic temperature β of 318 K. Enthalpy-entropy compensation effect was observed in the reactions with all the examined 4-nitrophenyl benzoates. The relation between the reactivity and polarizability of nucleophilic center in S-and O-nucleophiles is discussed.

Substituent effects in nucleophiles on activation parameters in the bimolecular nucleophilic reactions in solution

Changes of the activation parameters, ΔH‡ and ΔS‡, in the SN2, SNV, AdN, SNAr and acyl-transfer reactions with phenol, aniline and pyridine nucleophiles in various solvents were correlated with σ constants of the substituents in the aromatic ring of the nucleophiles. The resultant δΔH‡ and δΔS‡ reaction constants are linearly related for variations of substituents at the nucleophile. Correlation of δΔH‡vs. δΔS‡ allow the estimation of the contribution of changes of the internal enthalpy, δΔH‡int, to the enthalpy reaction constant, δΔH‡, which gives a single linear dependence on the Hammett ρ reaction constants for all bimolecular nucleophilic reactions. The deviations from dependence of δΔH‡intvs. ρ can be interpreted in terms of changes of the transition state structure or reaction mechanism. The results obtained show that the substituent effects in the nucleophiles on the charge development in the transition state are governed by the magnitude of δΔH‡int.

Photocyclization of 2-azido-1-(4-tert-butylphenoxy)-9,10-anthraquinone in the presence of substituted phenols

New types of phototransformations in the quinone series, viz., photocyclizations of 1-aryloxy-2-azido-9,10-anthraquinone in the presence of phenols, were studied. The photolysis affords mainly 5H-naphtho[2,3-c]phenoxazine-8,13-diones, in which the nitrogen atom is covalently bound to the phenyl ring of the attached phenol. As a result, complex polycyclic derivatives of phenoxazines were prepared in high yields in one step.