Lev M. Yagupolskii

Equilibrium acidities of superacids.

In this paper, we report the most comprehensive equilibrium superacidity scale that is available to date. Contrary to most of the past works, this scale is set up in a medium of constant composition and the obtained acidity values characterize the acidities of molecules rather than acidities of media. The current scale is thus complementary to the well-known H(0) scale in the information that it provides. The solvent used is 1,2-dichloroethane (DCE). DCE has very weak basic properties (but sufficiently high polarity) and is an appropriate solvent for measuring acidities of very strong acids of diverse chemical nature. DCE acidities of well-known superacids (CF(3)SO(2)OH, (CF(3)SO(2))(2)NH, cyanocarbon acids, etc.) as well as common mineral acids (H(2)SO(4), HI, HBr, etc.) are reported. Acidities of altogether 62 acids have been determined from 176 interlinked relative acidity measurements. The scale spans 15 orders of magnitude (from picric acid to 1,1,2,3,3-pentacyanopropene) and is expected to be a useful tool in design, use, and further acidity measurements of superacidic molecules.

Revision of the Gas-Phase Acidity Scale below 300 kcal mol-1

The gas-phase acidity (GA) scale from (CF(3)CO)(2)NH to (C(2)F(5)SO(2))(2)NH--about a 24 kcal mol(-1) range of gas-phase acidities--was reexamined using the Fourier transform ion cyclotron resonance equilibrium measurement approach. Some additions and modifications to the standard methodology of GA measurements were introduced (estimation of partial pressures from mass spectra of the compounds, instead of the pressure gauge readings and use of long reaction times) to achieve higher reliability. Gas-phase acidities of 18 compounds were determined for the first time. The results reveal a contraction of the previously published values in this part of the scale. In particular, the GA values of (CF(3)SO(2))(2)NH and (C(2)F(5)SO(2))(2)NH (important components of lithium ion battery electrolytes and ionic liquids) were revised toward stronger acidities from 291.8 kcal mol(-1) to 286.5 kcal mol(-1) and from 289.4 kcal mol(-1) to 283.7 kcal mol(-1) (i.e., by 5.3 and 5.7 kcal mol(-1)), respectively. Experimental and computational evidence is presented in support of the current results.

SUPERACIDITY OF NEUTRAL BRONSTED ACIDS IN GAS PHASE

Quantum chemical calculations of potentially superacidic neutral Brönsted acids were carried out using the PM3 method. It was shown that the PM3 method can be used to predict the gas phase acidities of acidic compounds only if empirical corrections are made. A strong acidifying effect is predicted for a new family of compounds in which an sp2 oxygen is substituted by an (DOUBLE BOND) NSO2CF3 group. So, for example, such replacement is expected to result in acid strengthening by 47.5 kcal/mol in the case of CH3CHO and by 22.7 kcal/mol in the case of CF3SO2OH. The acidities of such compounds are predicted to be increased further (nonadditively) by stepwise replacements of (DOUBLE BOND) O by (DOUBLE BOND) NSO2CF3. The geometries of known superacidic systems were reproduced quite well by PM3 method. The geometries of several superacidic systems were analyzed.

The immense acidifying effect of the supersubstituent NSO2CF3 on the acidity of amides and amidines of benzoic acids in acetonitrile

The pKa values of acidic dissociation of the conjugate acids of derivatives of benzoate anions, where one or two oxygen atoms are replaced by an NSO2CF3 group, N-aroyltrifluoromethanesulfonamides 1a–f and previously unreported N,N′-bis(trifluoromethylsulfonyl)benzamidines 4a–f, were measured in acetonitrile. In the case of the parent compound, the incorporation of the first NSO2CF3 group instead of the oxygen atom leads to a sharp (by 9.6 pKa units) increase in the acidity, whereas the replacement of the second oxygen atom results in a further huge increase in the acidity by 4.9 powers of ten. It was found that the sensitivity of the reaction series under consideration towards substituent effects (in the benzene ring) decreases in the following order: benzoic acids > benzamides (1a–f) > benzamidines (4a–f). The results of this work carry potentially important implications for the design of new types of superacids and catalytic materials.

Torsion potentials and electronic structure of trifluoromethoxy- and trifluoromethylthiobenzene: an ab initio study

Abstract Potential functions of internal rotation about the Csp2ue5f8X bonds in molecules C6H5XCF3 (X=O, S) were calculated at the second-order Moller–Plesset perturbation level of theory with 6-31G(d) basis set. The profile of the potential function and the rotation barrier (ΔE#=3.0xa0kJ/mol) found for C6H5OCF3 suggest that, depending on experimental conditions, there can be either free rotation about the Csp2ue5f8O bond or the conformational equilibrium is shifted to the side of the orthogonal form. The rotational barrier for C6H5SCF3 is 14.7xa0kJ/mol and the molecule exists in the stable orthogonal conformation. The nature of hybridization, energy and population of lone electron pairs (LPs) on the oxygen and sulfur atoms were considered by using the Natural Bond Orbital (NBO) method. The energy of interactions of the LPs with antibonding π∗-orbitals of the aromatic moiety were estimated for different conformations. The distribution of electron density in the molecules was discussed. The results were compared with analogous calculations on the molecules C6H5XCH3.

New trends in the chemistry of aromatic compounds with fluorine-containing substituents

Abstract Recently, new methods for the introduction of fluorine-containing substituents into aromatic compounds have been developed in our Department and new types of organic substances synthesized. Emphasis has been placed not only on the ‘classic’ groups, such as the fluorine atom or perfluoro-alkyl and -alkenyl fragments, but mainly on substituents with perfluoroalkyl groups separated from the nuclei by the heteroatoms oxygen, sulfur (in valency states 2, 4 and 6), nitrogen and metals. We have also developed new principles for the construction of super-strong electron-withdrawing substituents and super-strong acids. This approach consists in replacing the sp 2 -oxygen atom in various groups with the =NSO 2 CF 3 radical and has been confirmed by examples of substituents with the central atoms consisting of sulfur in different valence states, carbon, phosphorus and iodine. From this principle, a stable substituent with σ p constant 1.76, equal to three nitro groups in its influence towards benzene nuclei, has been constructed.

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. n 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. n 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.

Halogeno and pseudohalogeno difluoromethanesulfonylfluorides

Abstract New substituted cyano-and isocyanatodifluoromethanesulfonylfluorides were synthesized and their properties compared with halogenodifluoromethanesulfonylfluorides. NMR parameters are related to the electronegativity and covalent radii of substitutents.

Alkyl derivatives of bis(perfluoroalkylsulfonylimino)trifluoromethanesulfonic acid.

N-methyl and N-ethyl derivatives of N-(trifluoromethylsulfonyl)-[N-(trifluoromethylsufonyl)-trifluoromethylsulfoximidoyl] imides 2a,b were prepared by alkylation of bis(trifluoromethylsulfonylimino)trifluoromethanesulfonic acid 1 or its silver salt 1a. It turns out that these imides are strong alkylating agents in spite of the fact that Me (Et) groups are attached to nitrogen atom. The alkylating activity of n-PrI, i-PrI, n-BuI, and n-AmI in the presence of silver salt of bis(trifluoromethylsulfonylimino)trifluoromethanesulfonic acid 1a was investigated.

Chemical properties of N-polyfluoroethylimidazole and -pyrrole derivatives

Bromination, acylation, nitration, and metallation of imidazole and pyrrole derivatives containing the difluoromethylene fragment at the N atom were studied. 1-(1,1,2,2-Tetrafluoroethyl)pyrrole, 1-(1,1,2,2-tetrafluoroethyl)imidazole, and 1-(2-chloro-1,1,2-trifluoroethyl)imidazole were used as substrates. 1-Alkyl-3-(1,1,2,2-tetrafluoroethyl)- and 1-alkyl-3-(2-chloro-1,1,2-trifluoroethyl)imidazolium iodides were obtained. These can be used as intermediates for preparation of new ionic liquids of the imidazole series and 1-alkyl-3-polyfluoroethylimidazole-2-thiones.