Double proton shifts in associates of formic acid with hydrides of third period elements

The mechanisms of double proton shift in associates HC(O)OH ... X of formic acid with hydrides (X = SiH₄, PH₃, PH₅, H₂S, SH₄, CIH, and CIH₃) were studied by theab initio method (SCF/3G*). The activation barriers to this reaction in associates with PH₃, H₂S, SH₄, CIH, and CIH₃ are equal to 68.3, 10.0, 26.0, 1.0, and 0.4 kcal mol^–1, respectively. For X = SiH₄ and PHS₅ transition states for the double proton shift were not determined, and in all of the other cases studied they are synchronous (concerted or one-step).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 817–822, April, 1996.     

Double proton shifts in associates of formic acid with CH4, NH3, H2O,CH3F,NH2F,HOF, and HF molecules

The mechanisms of double synchronous proton transfer in associates of formic acid with solvent molecules of the HC(O)OHX (X = CH₄, NH₃, H₂O, or HF) and HC(O)OHFHY (Y = CH₃F, NH₂F, HOF, F₂, or HF) types have been studied by anab initio (SCF/3G) method. The calculated activation barriers of the reactions are 78.52, 17.72, 9.91, and 7.06 kcal mol^–1 in the former case and 120.1, 259.4, 228.7, 182.8, and 0.35 kcal mol^–1 in the latter case. In the latter case, simultaneously with the double transfer of protons, migration of two fluorine atoms along the chain of the associate occurs.Dedicated to Academician of the RAS N. S. Zefirov (on his 60th birthday).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1690–1700, September, 1995.The present work was carried out with financial support from the Russian Foundation for Basic Research (Project Nos. 93-03-4972 and 93-03-18692) and the International Science Foundation (Grant ISF RNJ 000).     

Four-proton migrations in associates of two molecules of formic acid with two molecules of water or hydrogen fluoride

The mechanisms of proton transfer in associates of two molecules of formic acid with two molecules of water or hydrogen fluoride were studied usingab initio (SCF/6-31G^**) method. Cooperative (concerted, or one-step) four-proton transfer occurs in the associates studied. The structures of the transition states are in complete agreement with the previously proposed concept of stereochemical correspondence for cooperative reactions. The calculated energy barriers to cooperative proton transfer in the associates investigated are 32.9 and 24.2 kcal mol^–1, respectively.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2636–2640, November, 1996.     

Electrocatalytic formation of polymolecular products at the cathodic polarization of polycrystalline chromium in sulfuric acid solutions of formic and oxalic acids

The cathodic behavior of polycrystalline Cr electrodes in sulfuric acid solutions of oxalic (OA) and formic (FA) acids is studied by cyclic voltammetry. These organic substances not only chemisorb on the electrode surface thus severely hindering the hydrogen evolution on the metal but also take active part in the electrocatalytic reactions that occur under these conditions. The use of methods of chromatography mass spectrometry and photon-correlation spectroscopy demonstrates that long-term cathodic polarization of Cr in the potential range of active hydrogen evolution (in the vicinity of ?1.0 V) in sulfuric acid solutions containing FA and OA leads to the formation of polymolecular compounds. Among the latter, linear hydrocarbons and carboxylic acids containing 12–27 carbon atoms are isolated and identified.     

Proton migrations in associates of two molecules of formic acid with one molecule of hydrazine or hydrogen peroxide

The mechanisms of the proton transfer in associates of two molecules of formic acid with one molecule of hydrazine or hydrogen peroxide were studied usingab initio (SCFj6-31G^**) method. The mechanism of cooperative (concerted, one-step) four-proton transfer is realized in the associate with the hydrazine molecule. The proton transfer occurs stepwisevia an intermediate in the associate with a hydrogen peroxide molecule. The calculated activation barriers to the proton transfer in the associates investigated are 34.7 kcal mol^–1 and 27.1 kcal mol^–1, respectively.Translated fromlzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2631–2635, November, 1996.     

A synergetic effect in nitrous acid formation by sonolysis of nitric acid in the presence of nitrous oxide

A synergetic effect is found in the sonochemical formation of HNO₂ in HNO₃ solution in the presence of an N₂O–Ar gaseous mixture. The maximum rate of HNO₂ formation is observed at an N₂O : Ar ratio of 15 : 85 (v/v). During the sonolysis of 4 M HNO₃ solutions, the rate of HNO₂ formation increases multifold due to the synergetic effect. The rate of sonochemical hydrazine decomposition in nitrate solutions also increases considerably in the presence of N₂O.     

Tunneling dynamics of internal rotation in the nitric acid molecule

The Hamiltonian of internal rotation about theC ₂ axis in the HNO₃ molecule and its H/D-, O¹⁸/O¹⁶-, and N¹⁵/N¹⁴-isotopomers was reconstructed using the results of quantumchemical calculations. The Fermi resonance between the torsional (2v₉) and ONO bending (v₅) vibrations is a characteristic feature of the molecule. Tunneling splittings in the ground and excited states were calculated using the perturbative instanton approach. Abnormally large changes in the splittings upon isotope substitution of heavy atoms are predicted. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2052–2060, November, 1999.     

Pathways of the reaction of nucleophilic addition of ammonia to formaldehyde in the gas phase and in the complex with formic acid:ab initio calculations

The gradient pathways of the reaction of nucleophilic addition of ammonia to formaldehyde were calculated for free molecules and in the NH₃...H₂CO...HC(O)OH complex by theab initio RHF/6-31G^**, MP2(fc)/6-31G^**, and MP2(full)/6-311++G^** methods. Both reactions proceed concertedly. In the first case, the reaction successively passes through two transitional states with an energy barrier exceeding 35 kcal mol⁻¹. In the case of the complex with formic acid, the reaction follows a conventional pathway, although its activation barrier calculated by the RHF/6-31G^** and MP2(fc)/6-31G^** methods decreases to 12.6 and 3.8 kcal mol⁻¹, respectively. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 13–20, January, 1998.     

First steps of the reactions of alkanes and arenes with adamantyl cations in sulfuric acid in comparison with other reagents

Solutions of 1-adamantanol in sulfuric acid at T < 100 °C interact with alkanes (RH, [H₂SO₄] > 85%) and arenes (ArH, [H₂SO₄] > 59%). The data on the kinetics, kinetic isotope effect (KIE), effects of the structure of RH and ArH and acidity of the medium, and the observation of 1,4-cis-dimethylcyclohexane isomerization indicate that adamanyl cations (Ad⁺) serve as reactive species. In the reactions with alkanes, the Ad⁺ cation abstracts the hydride ion from RH in the rate-determining step. Compensation dependences appear between the activaion parameters for the KIE and “effect 5/6” (ratio of the rate constants for the C–H bond cleavage in cyclopentane and cyclohexane) in the reactions of cycloalkanes with Ad⁺ and other electrophilic reagents, such as “anthracene” (An₂)H⁺ and hydroxymethyl (CH₂OH)⁺ cations and Hg^II ions, including the points of the lower selectivity limit (k _H/k _D) = 1.4, (“5/6”) = 1. In the reactions with the Ad⁺ cation, the bond selectivity 3⁰: 2⁰ of alkanes is higher, while 2⁰: 2⁰ is lower compared to other reagents. In the first case, the selectivity is probably determined predominantly by the energies of the cleaved C–H bonds, whereas in the second case it is determined by steric hindrances. Judging by the kinetic and selectivity data in the series benzene—toluene—o-xylene—m-xylene and the absence of the reaction with p-xylene, mesitylene, and pseudocumene, it can be concluded that the main contribution to the Ad⁺ + ArH interaction is made by adamantylation to the para- and meta-positions of the benzene ring, whereas the ortho-positions are inaccessible to the attack because of steric hindrances. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1581–1596, August, 2008.     

Double proton transfer and one-electron oxidation behavior in double H-bonded glycinamide-glycine complex in the gas phase

The behaviors of double proton transfer (DPT) occurring in a representative glycinamide-glycine complex have been investigated employing the B3LYP/6-311++G** level of theory. Thermodynamic and especially kinetic parameters, such as tautomerization energy, equilibrium constant, and barrier heights have been discussed, respectively. The relevant quantities involved in the DPT process including geometrical changes, interaction energies, and deformation energies have also been studied. Analogous to that of tautomeric process assisted with a formic acid molecule, the participation of a glycine molecule favors the proceeding of the proton transfer (PT) for glycinamide compared with that without mediator-assisted case. The DPT process proceeds with a concerted mechanism rather than a stepwise one because no zwitterionic complexes have been located during the DPT process. The barrier heights are 12.14 and 0.83 kcal/mol for the forward and reverse directions, respectively. However, both of them have been reduced by 3.10 and 2.66 kcal/mol to 9.04 and -1.83 kcal/mol with further inclusion of zero-point vibrational energy (ZPVE) corrections, where the disappearance of the reverse barrier height implies that the reverse reaction should proceed with barrierless spontaneously, analogous to those of DPTs occurring between glycinamide and formic acid (or formamide). Additionally, the oxidation process for the double H-bonded glycinamide-glycine complex has also been investigated. The oxidated product is characterized by a distonic radical cation due to the fact that one-electron oxidation takes place on glycine fragment and a proton has been transferred from glycine to glycinamide fragment spontaneously. As a result, the vertical and adiabatic ionization potentials for the neutral complex have been determined to be about 8.71 and 7.85 eV, respectively, where both of them have been reduced by about 0.54 (1.11) and 0.75 (1.13) eV relative to those of isolated glycinamide (glycine) due to the formation of the intermolecular H-bond.     

Electrical conductivity study of the self-association of ionic surfactants in solution in ethyleneglycol,formic acid and formamide

The self-association of several cationic surfactants has been investigated by means of solubility and electrical conductivity measurements in ethyleneglycol, formic acid and formamide. Operational critical micelle concentrations (CMC_op) have been obtained from the vs. surfactant concentrationC plots by the usual interpolation procedure. It has been found that for the surfactant-solvent systems investigated the value of CMC_op increases with the extent of theC-range investigated. This result together with others concerning the effect of temperature and surfactant chain length reveal that the CMC_op-values have an ambiguous meaning concerning the surfactant self-association. Comparison of the vs.C plots for cetyltrimethylammonium chloride and tetramethylammonium chloride, for instance, reveals that some surfactant self-association takes place, probably leading to small, highly ionized surfactant aggregates, but the systems do not show true critical micelle concentration. Solubility measurements as a function of temperature lead to the same conclusion. The results are discussed according to our present understanding of the process of micellization and the necessity of using solvents of very high cohesive energy density in order to observe, with ionic surfactants, true CMCs corresponding to a highly cooperative association process. This appears to be the case only with water and hydrazine, not with formamide and other less cohesive solvents.     

Intermolecular interactions of formic acid with benzene: Energy decomposition analyses with ab initio MP2 and double‐hybrid density functional computations

The intermolecular interactions of formic acid (HCOOH) with benzene (C₆H₆) have been investigated using localized molecular orbital energy decomposition analyses (LMO‐EDA) with ab initio MP2 and several double‐hybrid density functionals. The molecular geometries of five HCOOH…C₆H₆ complexes and corresponding benchmark total interaction energies at the CCSD(T)/CBS level are taken from literature (Zhao et al., J. Chem. Theory Comput. 2009, 5, 2726). According to the results of LMO‐EDA with the MP2 method, the dispersion energies are found to be as important as the electrostatic energies for the total interaction energies of the five HCOOH…C₆H₆ complexes. Based on LMO‐EDA with the double‐hybrid density functionals of B2PLYP, B2K‐PLYP, B2T‐PLYP, and B2GP‐PLYP computations, two new parameters for the framework of B2PLYP are extrapolated. These two new parameters are tested with other 10 complexes involving C₆H₆ (Crittenden, J. Phys. Chem. A 2009, 113, 1663), and they perform well on predicting the corresponding total interaction energies. Interestingly, these two new parameters for the framework of B2PLYP also perform well on the noncovalent complexation energies database (NCCE31/05) developed by Truhlar's group (Zhao and Truhlar, J. Phys. Chem. A 2005, 109, 5656). Therefore, these two new parameters appear to be suitable for investigating the noncovalent interactions, and they are denoted as B2N‐PLYP, where N stands for the noncovalent interaction. This study is expected to provide new insight into the derivation of double‐hybrid density functionals for studying the noncovalent interactions. © 2013 Wiley Periodicals, Inc.     

Pathways of the reactions of nucleophilic addition of H2O and HF molecules to formaldehyde in the gas phase and in the complex with formic acid:ab initio calculations

The gradient pathways of the reactions of nucleophilic addition of H₂O and HF molecules to formaldehyde in the gas phase and in the XH…H₂CO…HC(O)OH complex (X=OH, F) were calculated by theab initio RHF/6-31G^**, MP2(fc)/6-31G^**, and MP2(full)/6-311++G^** methods. Both reactions proceed concertedly. The formation of H-bonded bimolecular pre-reaction complexes is the initial stage of the gas-phase reactions; at the same time, no indications of the formation of stable π-complexes were found on the potential energy surfaces of systems under study. The calculated energy barriers to the gasphase reactions exceed 40 kcal mol⁻¹, while those to reactions in the complex XH…H₂CO…HC(O)OH (X=OH, F) become more than halved. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2146–2154, November, 1998.     

Comparative quantum chemical studies in the framework of Gaussian approximations of the acidic characteristics of the simplest zeolite clusters and of the sulfuric acid molecule

Different variants of the Gaussian approximation, giving the energetic characteristics of molecules with chemical accuracy (±2 kcal mol^–1), are applied to calculations of the deprotonation energy of the sulfuric acid molecule in the gas phase as well as to the simplest clusters modeling the bridging hydroxyl groups in zeolites, The conclusion is made that the bridging hydroxyls am more acidic than the sulfuric acid molecule. The estimated range of deprotonation energy in zeolites (275±15 kcal mol^–1), is in good agreement with experimental data and with results ofab initio calculations for extended models including several tens of atoms. The effects of the quality of the basis set and electron correlation on deprotonation energy are also discussed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 7, pp. 1641–1647, July, 1996.     

Kinetics, selectivity, and mechanism of the reactions of arenes with adamantyl carbocations in sulfuric acid

Data on the kinetics, selectivity, kinetic isotope effect, and the effect of the acidity of the medium on the rate of the reactions of benzene and alkylbenzenes in sulfuric acid (59–78 wt.% H₂SO₄) solutions of 1-adamantanol at 30 °C indicate that the direct reagents are the adamantyl carbocations (Ad⁺) that alkylate the arenes. The ortho positions of the benzene ring are not accessible on account of steric hindrances. The rate of attack by the Ad⁺ cation on the accessible para and meta positions of the ring is controlled by the formation of a σ complex. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 1, pp. 14–18, January–February, 2006.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids I. Separation of benzenecarboxylic acids with tartaric acid as eluent and with UV-photometric detection

The application of zirconium-modified silica gels (Zr–Silicas) as stationary phases for ion-exclusion chromatography with UV-photometric detection (IEC–PD) for mono-, di-, tri- and tetrabenzenecarboxylic acids (pyromellitic, trimellitic, hemimellitic, o-phthalic, salicylic and benzoic acids) and phenol was carried out using tartaric acid as the eluent. Zr–Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. The effect of the amount of zirconium adsorbed on silica gel on chromatographic behavior of these benzenecarboxylic acids and phenol was investigated. As a result, Zr–Silica adsorbed on 20 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in the IEC–PD for the simultaneous separation of these benzenecarboxylic acids and phenol. Excellent simultaneous separation and highly sensitive UV detection at 254 nm for these benzenecarboxylic acids and phenol were achieved in 20 min by the IEC–PD using the Zr–Silica column (250×4.6 mm I.D.) and a 10 mM tartaric acid at pH 2.5 as eluent.     

Application of zirconium-modified silica gel as a stationary phase in the ion-exclusion chromatography of carboxylic acids II. Separation of aliphatic carboxylic acids with pyromellitic acid as eluent and with suppressed conductimetric detection

The application of zirconium-modified silica gels (Zr-Silica) as stationary phases for ion-exclusion chromatography with conductimetric detection (IEC–CD) for C₁–C₈ aliphatic carboxylic acids (formic, acetic, propionic, butyric, valeric, caproic, heptanoic and caprylic acids) was carried out using pyromellitic acid as the eluent. Zr-Silicas were prepared by the reaction of the silanol group on the surface of silica gel with zirconium tetrabutoxide [Zr(OCH₂CH₂CH₂CH₃)₄] in ethanol solution. An ASRS-Ultra anion self-regenerating suppressor in the K⁺ form was used for the enhancement of conductimetric detector response of these aliphatic carboxylic acids. A Zr-Silica adsorbed on 10 mg zirconium g⁻¹ silica gel was the most suitable stationary phase in IEC–CD for the separation of these aliphatic carboxylic acids. Excellently simultaneous separation and highly sensitive detection for these aliphatic carboxylic acids were achieved in 25 min by IEC–CD with the Zr-Silica column (250×4.6 mm I.D.) and a 0.2 mM pyromellitic acid containing 0.15% heptanol as the eluent.     

Synthesis,characterization, and pharmacological evaluation of the proton transfer salts of 2-aminobenzothiazole derivatives with 5-sulfosalicylic acid and their Cu(II) complexes

Abstract

Two proton transfer compounds, formed between 2-aminobenzothiazole derivatives (2-aminobenzothiazole (abt) and 2-amino-6-ethoxybenzothiazole (EtOabt)) and 5-sulfosalicylic acid dihydrate (H₃ssa) as parent compounds, (Habt)⁺(H₂ssa)^? (1) and (HEtOabt)⁺(H₂ssa)^? (2) and their Cu(II) complexes (3 and 4, respectively) have been prepared and characterized using spectroscopic techniques. The single crystal X-ray diffraction method has been also applied to 3 and 4. Although 3 has a distorted octahedral form, 4 exhibits a distorted square pyramidal geometry. All compounds, including saline and diclofenac sodium as standards, have been evaluated pharmacologically for their anti-inflammatory and analgesic activities in rats and mice. Parent compounds (abt, EtOabt, and H₃ssa) 3 and 4 show significant anti-inflammatory and analgesic activities as compared with control compounds.     

Theoretical study on the reactions of Nb and Nb+ with CO2 in gas phase

Density functional theory calculations have been performed to explore the potential energy surfaces of C? O bond activation in CO₂ molecule by gas‐phase Nb atom and Nb⁺ cation for better understanding the reaction mechanism of second‐row metal with CO₂. The minimum‐energy reaction path is found to involve the spin inversion in the different reaction steps. This potential energy curve‐crossing dramatically affects the reaction energetic. The present results show that the mechanism is insertion‐elimination mechanism along the C? O bond activation reaction. All theoretical results not only support the existing conclusions inferred from early experiment but also complement the pathway and mechanism for this reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Cross-polarization with magic-angle spinning kinetics and impedance spectroscopy study of proton mobility,local disorder,and thermal equilibration in hydrogen-bonded poly(methacrylic acid)

The ¹H–¹³C cross-polarization with magic-angle spinning (CP MAS) kinetics was studied in poly(methacrylic acid) (PMAA) having the purpose to track the links between the local order in the main chain and the proton dynamics in peripheral hydrogen bond networks. The experimental CP MAS kinetic curves were analyzed applying the models of isotropic and anisotropic spin-diffusion with thermal equilibration. The fractal dimension D_p ≈ 3 was deduced that indicates that PMAA behaves as an isotropic 3D-system. No proton conductivity in the neat PMAA was deduced from the impedance spectroscopy data analyzing the frequency dependences of the complex dielectric permittivity. The value of local order parameter S = 0.70 for CH₂ in PMAA occupies an intermediate position between 0.63 and 0.85 deduced for CH₂ sites in the main chains of poly(vinyl phosphonic acid) and poly(2-hydroxyethyl methacrylate), that is, the true proton conductor and the polymer that contains the H-bond network, however, no proton conductivity, respectively.