Decomposition of hydrogen peroxide in protic and polar aprotic solvents on TS-1 heterogeneous catalyst

Kinetic parameters of H₂O₂ decomposition in methanol, propanol-1, propanol-2, acetone, and acetonitrile at 30–55°C on a TS-1 heterogeneous catalyst were determined. Recommendations are given on choice of solvents in oxidation of organic compounds with hydrogen peroxide.     

The effect of the medium polarity on the mechanism of the reaction of hydroxybenzenes with hydrazyl radical in aprotic solvents

Mechanisms of the reaction of di- and trihydroxybenzenes with 2,2′-diphenyl-1-picrylhydrazyl (stable radical) in aprotic media of different polarity have been elucidated by experimental and quantum-chemical methods. Kinetic, stoichiometric, and activation parameters of the reaction have been determined. In benzene (nonpolar solvent), the studied reaction occurs via the hydrogen atom transfer mechanism; in the polar solvent with weak ionizing ability (i.e. DMSO), the reaction predominantly occurs via the faster mechanism of coupled electron and proton transfer.     

Hydroxylation of phenol with hydrogen peroxide in protic and aprotic solvents on TS-1 catalyst

Hydroxylation of phenol with a 25% aqueous solution of hydrogen peroxide in polar protic and aprotic solvents on TS-1 heterogeneous catalyst under various conditions was studied. The major reaction products (hydroquinone, pyrocatechol) and their ratio were determined. A kinetic model describing the hydroxylation in accordance with the Rideal-Eley mechanism was chosen.     

Cellulose solutions in dipolar aprotic solvents

Preparation conditions and properties of cellulose solutions in DMAA containing 7–8% lithium chloride are considered. Investigation of the optical anisotropy and structure of cellulose solutions in this solvent confirms that the LS state is attained with an increase in the concentration of cellulose. On the basis of these cellulose solutions, fibers not ranking below viscose fibers in mechanical properties are prepared. The use of a mixed solution of 95% cellulose and 5% poly(amidobenzimidazole) in DMAA containing 7% lithium chloride makes it possible to prepare films and fibers whose strength is more than two times greater than the strength of cellulose hydrate fibers. The deformation-driven orientation and supramolecular structure of fibers and films are studied by spectroscopy and small-angle scattering of polarized light.     

One- vs. two-electron oxidations of tetraarylethylenes in aprotic solvents

The oxidation of dimethylaminophenyl substituted ethylenes and tetra-p-anisyl ethylene at a platinum electrode in methylene chloride and acetonitrile solutions was investigated by cyclic and rotating disk electrode voltammetry, potential step chronocoulometry, controlled potential coulometry and e.s.r. spectroscopy. The results show that the oxidations occur by either two one-electron steps or by a single two-electron step depending upon the structure of the molecule. Factors influencing the reaction path are discussed.     

Polarography of organic compounds in aprotic solvents

A review of the polarography of organic compounds in aprotic solvents is presented.     

Complexes of acid amides with aprotic polar solvents IV. Complexes of poly(acid amides) with aprotic solvents

The process of solid-phase cyclodehydration of films cast from solutions of poly(acid amides) (PAA) in dimethylformamide, dimethylacetamide and N-methyl-2-pyrrolidone has been investigated by mass-spectrometric thermal analysis (MTA). It is shown that MTA is a structure-sensitive method making it possible to follow the appearance and changes in the character of ordered structures formed in PAA films. The authors relate these structures to the process of crystallization of complexes of PAA with aprotic polar solvents.     

Extraction of eleutherococcus by aprotic solvents

V. V. Kuibyshev Tomsk State University. Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 143–144, January–February, 1989.     

Rotational diffusion in aprotic and protic solvents

We present the orientational relaxation times in protic and aprotic solvents for rose bengal in its lowest excited singlet state. The method uses a mode locked dye laser for polarized excitation, and time correlated single photon counting for determination of the time resolved polarized fluorescence. The observed orientational decay for the dipolar aprotic solvents and the alcohols are in agreement with the values predicted by the Stokes-Einstein diffusion equation. In the latter solvents, volume and shape corrections must be made for attachment of the alcohol to the two anion sites of the dye molecule. The solvent N-methylformamide, however, shows rose bengal reorienting much faster than the alcohols. Our interpretation of this data suggests that agreement with the Stokes-Einstein equation (stick boundary conditions) is coincidental. We propose a solvent torque model in which the solvent interaction at each anion site of rose bengal controls the deviations from an expected slip boundary condition. This qualitative model is used to correlate our data as well as relevant data in the literature. The values in picoseconds for the observed orientational relaxation times are given in parenthesis; acetone (70), DMF (160), DMSO (420), MeOH (190), EtOH (450), isopropanol (840), NMF (500).     

Cellulose decomposition behavior in hot-compressed aprotic solvents

Microcrystalline cellulose (avicel) is treated in hot-compressed aprotic solvents,sulfolane and 1,4-dioxane,using a batch-type reaction system with a molten tin bath in a range from 290 to 390℃. The corresponding densities of the solvent are 0.25-1.26 g/cm3 and 0.21-1.03 g/cm3 for sulfolane and 1,4-dioxane,respectively. As a result,in both solvents,more than 90% of cellulose is found to be de-composed to the solvent-soluble portion in which levoglucosan is the main component with the high-est yield of about 35% on original cellulose basis. The decomposition rate to levoglucosan is,however,faster in sulfolane than in 1,4-dioxane,while levoglucosan is more stable in 1,4-dioxane. In addition,its yield is found to be solvent-density dependent to be highest around 0.4-0.5 g/cm3 for both solvents. To elucidate these decomposition behaviors,the results obtained in this study with aprotic solvents are compared with protic solvents such as water and methanol in previous works.     

Proton solvation in protic and aprotic solvents

Protonation pattern strongly affects the properties of molecular systems. To determine protonation equilibria, proton solvation free energy, which is a central quantity in solution chemistry, needs to be known. In this study, proton affinities (PAs), electrostatic energies of solvation, and pK_A values were computed in protic and aprotic solvents. The proton solvation energy in acetonitrile (MeCN), methanol (MeOH), water, and dimethyl sulfoxide (DMSO) was determined from computed and measured pK_A values for a specially selected set of organic compounds. pK_A values were computed with high accuracy using a combination of quantum chemical and electrostatic approaches. Quantum chemical density functional theory computations were performed evaluating PA in the gas‐phase. The electrostatic contributions of solvation were computed solving the Poisson equation. The computations yield proton solvation free energies with high accuracy, which are in MeCN, MeOH, water, and DMSO ?255.1, ?265.9, ?266.3, and ?266.4 kcal/mol, respectively, where the value for water is close to the consensus value of ?265.9 kcal/mol. The pK_A values of MeCN, MeOH, and DMSO in water correlates well with the corresponding proton solvation energies in these liquids, indicating that the solvated proton was attached to a single solvent molecule. © 2016 Wiley Periodicals, Inc.     

Effect of the solvent on the equilibria of acid-base indicators in aprotic and amphiprotic solvents

The dissociation constants of a series of indicators inN,N-dimethylformamide medium have been determined, and compared with those for the indicators in other aprotic solvents (dimethylsulphoxide and acetonitrile) and in some amphiprotic solvents (water, methanol, ethanol, propan-2-ol and tertbutanol). The effect of the solvent characteristics on the pK values have been evaluated, and the pK + p _ws ^t (H⁺) values shown to be linearly correlated with the Dimroth and ReichardtE _T ^N and acceptor number solvatochromic parameters.     

Electrochemical reduction of benzenesulphenyl chloride in aprotic solvents

The cathodic behaviour of benzenesulphenyl chloride has been studied at a platinum electrode in acetonitrile by using cyclic voltammetry and controlled potential electrolysis. It has been evidentiated that PhSCl gives rise, in an one-electron reduction process, to PhSSPh and Cl^? according to $2PhSCl+2{\mathit{e}}^{?}\to PhSSPh+2{Cl}^{?}$ The chloride ions so generated catalyze the subsequent hydrolysis of PhSCl caused by traces of water present in the organic solvent, i.e. $2PhSCl+H_{2}O\stackrel{{Cl}^{?}}{\to }PhSOSPh+2HCl$ which is concomitant with the electrodic reaction and hence accounts for the overall n_e value lower than one. The same results have been obtained in nitromethane while in dimethyl-formamide the above reported hydrolysis reaction seems to be catalyzed by the solvent itself.     

Complexes of acid amides with polar aprotic solvents. I

Complexes of bis(N-phenyl)-pyromellitic acid diamide with dimethylformamide were synthetized and studied by thermal mass-spectrometry. It was found that, depending on the precipitating agent applied, the composition of the complexes corresponded to 1 acid amide: 2 dimethylformamide or to 1 acid amide: 1 dimethylformamide. The effects of complex formation on the thermal cyclodehydration of bis(N-phenyl)-pyromellitic acid diamide and on the accompanying degradation processes are discussed.     

New protic salts of aprotic polar solvents

Aprotic polar solvents such as DMF, acetonitrile or DMSO can be protonated to form stable triflate salts when treated with triflic acid. The reaction of the same solvents with N,N-bis(trifluoromethanesulfonyl)imide led to the isolation of the corresponding N,N-bis(trifluoromethanesulfonyl)imide salts.