Identification of 1,3-dialkylimidazolium salt supramolecular aggregates in solution

The nature of the interactions between 1,3-dialkylimidazolium cations and noncoordinating anions such as tetrafluoroborate, hexafluorophosphate, and tetraphenylborate has been studied in the solid state by X-ray diffraction analysis and in solution by (1)H NMR spectroscopy, conductivity, and microcalorimetry. In the solid state, these compounds show an extended network of hydrogen-bonded cations and anions in which one cation is surrounded by at least three anions and one anion is surrounded by at least three imidazolium cations. In the pure form, imidazolium salts are better described as polymeric supramolecules of the type {[(DAI)(3)(X)](2+)[(DAI)(X)(3)](2-)}(n) (where DAI is the dialkylimidazolium cation and X is the anion) formed through hydrogen bonds of the imidazolium cation with the anion. In solution, this supramolecular structural organization is maintained to a great extent, at least in solvents of low dielectric constant, indicating that mixtures of imidazolium ionic liquids with other molecules can be considered as nanostructured materials. This model is very useful for the rationalization of the majority of the unusual behavior of the ionic liquids.     

Equilibrium CH acidity of heteroatomic monosubstituted acetylenes in dimethyl sulfoxide

Conclusions The transmetalation method in DMSO was used to measure the equilibrium CH acidity of a number of heteroatomic monosubstituted acetylenes, and it was shown that these compounds are relatively weaker CH acids in DMSO than in 1,2-dimethoxyethane.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2351–2352, October, 1975.     

Solvation and dynamic behavior of cyclodextrins in dimethyl sulfoxide solution

High-frequency dielectric relaxation behavior up to 20 GHz was investigated for plain (alpha, beta, gamma) and (62 and 100%) methylated cyclodextrins, CDs, in dimethyl sulfoxide, DMSO, solution. Each hydrogen atom of OH groups of the CDs solvated a DMSO molecule for a residence time of 130-180 ps due to the hydrogen bond formation to an oxygen atom of DMSO, and a few DMSO molecules were included in cavities of the CDs for a while similar to the residence time. The overall rotational relaxation modes of solvated CDs were also observed depending on the effective sizes of the solvated CDs.     

Adsorption process of phenothiazine solution in dimethyl sulfoxide on graphite electrodes

In this paper, an original solution for the modeling and simulation of the adsorption process of a phenothiazine derivative on graphite electrodes is presented. The adsorption process is considered a distributed parameter one, due to the fact that the adsorbed phenothiazine quantity is a function depending on two independent variables. The structure parameters of the adsorption process, which define the influence of both independent variables, are determined using an experimental identification method. The experimental data are obtained through an experiment which is based on the process step response. In order to simulate the adsorption process, the approximate analytical solution, representing the process model, is determined. The simulation results prove the model generality; it is being simulated in relation to both independent variables.     

Potentiometric titrations in non-aqueous solution : An empirical acidity potential scale of twelve solvents

The present study was aimed at finding practically applicable criteria for choosing suitable conditions for potcntiometric titration of acids and bases in non-aqueous solvents.To this end the acidity potential ranges of twelve solvents of widely varying properties, and the half-neutralization potentials (h.n.p.'s) in these solvents of sixteen acids of various types (including protonated bases), were determined.For the titration of acids new, strongly basic titrant solutions were developed, consisting of tetra-alkylammonium bases dissolved in pure pyridine.     

First-principle predictions of absolute pKa's of organic acids in dimethyl sulfoxide solution

MP2/6-311++G(d,p) and B3LYP/6-311++G(2df,p) methods were found to be able to predict the gas-phase acidities of various organic acids with a precision of 2.2 and 2.3 kcal/mol. A PCM cluster-continuum solvation method was developed that could predict the solvation free energies of various neutral, cationic, and anionic organic species in DMSO with a precision of about 2.0 kcal/mol. Using these carefully tested methods, we successfully predicted the pKa's of 105 organic acids in DMSO with a precision of 1.7-1.8 pKa units. We also predicted the pKa's of a variety of organosilanes in DMSO for the first time using the newly developed methods. This study was one of the first that employed first-principle methods for calculating pKa's of unrelated compounds in organic solutions.     

Structure of the hydrated and dimethyl sulfoxide solvated rubidium ions in solution

The structure of the hydrated and the dimethyl sulfoxide solvated rubidium ions in solution has been determined by means of large-angle X-ray scattering (LAXS) and extended X-ray absorption fine structure (EXAFS) studies. The models of the hydrated and dimethyl sulfoxide solvated rubidium ions fitting the experimental data best are square antiprisms with Rb-O bond distances of 2.98(2) and 2.98(3) A, respectively. The EXAFS data show a significant asymmetry in the Rb-O bond distance distribution with C(3) values of 0.0076 and 0.015 A(3), respectively. No second hydration sphere is observed around the hydrated rubidium ion. The dimethyl sulfoxide solvated rubidium ion displays a Rb-O-S bond angle of ca. 130 degrees, which is typical for a medium hard electron acceptor such as rubidium.     

Investigations on the structure of dimethyl sulfoxide and acetone in aqueous solution

Aqueous solutions of dimethyl sulfoxide (DMSO) and acetone have been investigated using neutron diffraction augmented with isotopic substitution and empirical potential structure refinement computer simulations. Each solute has been measured at two concentrations-1:20 and 1:2 solute:water mole ratios. At both concentrations for each solute, the tetrahedral hydrogen bonding network of water is largely unperturbed, though the total water molecule coordination number is reduced in the higher 1:2 concentrations. With higher concentrations of acetone, water tends to segregate into clusters, while in higher concentrations of DMSO the present study reconfirms that the structure of the liquid is dominated by DMSO-water interactions. This result may have implications for the highly nonideal behavior observed in the thermodynamic functions for 1:2 DMSO-water solutions.     

水/二甲基亚砜体系中无机盐高效催化木糖脱水制备糠醛(英)

提出了一种高效的均相催化木糖制备糠醛的方法,探讨了水/二甲基亚砜（DMSO）均相体系中不同类型的无机盐对催化木糖制备糠醛的影响.结果表明,氯盐较硫酸盐和硝酸盐表现出较高的催化活性,其中以SnCl₄的催化效果最高.且它与LiCl复配时催化性能更高.当SnCl₄的摩尔分数为0.8时,催化效果最好,糠醛收率达56.9%.反应条件优化实验发现,当催化剂与木糖的摩尔比为0.5:1,固液比为1:20,水与DMSO体积比为5:5时,于130℃下反应6h,糠醛收率达63%.     

Viscoelastic behavior of polyacrylonitrile/dimethyl sulfoxide concentrated solution with water

The spinnability and polydispersity of polyacrylonitrile/dimethyl sulfoxide (PAN/DMSO)/H₂O spinning solutions with conventional PAN molecular weight and comparative high PAN concentration have been investigated using a cone‐plate rheometer. It is observed from the measurements that, the viscosities of the solutions decreased with the rising of shear rate, and then stabilized to almost the same value, regardless of the PAN concentration. The chain orientation in the fiber formed under constant shear rate cannot be changed considerably even after long relaxation of more than 900s. For dynamic experiments, a steady increase of both G′ and G″ with escalating oscillation frequency was seen for all samples. Higher viscous‐elastic modulus at higher H₂O content was found, too. It is also concluded from the log G′ ? log G″ plot and the gel point that the PAN/DMSO/H₂O system with regular PAN molecular weight behaves very close to a mono‐disperse system, thus very suitable for gel spinning and for preparation of high performance PAN precursor fiber. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1437–1442, 2009     

Thermolysis of dimethyl sulfoxide

The thermal decomposition of dimethyl sulfoxide at small extent of reaction has been studied at temperatures of 297-350°C and pressures of 10–400 Torr. The major products CH₄, C₂H₄, and SO₂ were shown to follow first-order kinetics. The activation energies for production of each was about 48 kcal·mole^?1. A chain mechanism has been postulated in the light of the results of isotopic substitution experiments.     

Kinetics and mechanism of oxidation of dimethyl sulfoxide by chloramine-T in aqueous solution

The kinetics of oxidation of dimethyl sulfoxide (DMSO) by chloramine-T (CAT) is studied in HClO₄ and NaOH media with OsO₄ as a catalyst in the latter medium. In acid medium, the rate law is -d [CAT]/dt = k [CAT][DMSO][H⁺]. Alkali retards the reaction and the rate law takes the form -d [CAT]/dt = k [CAT][DMSO][OsO₄]/[NaOH], but is reduced to -d [CAT]/dt = k [CAT][DMSO] at higher alkali concentrations. The reaction is subjected to changes in (a) ionic strength, (b) concentrations of added neutral salts, (c) concentrations of added reaction product, (d) dielectric constant, and (e) solvent isotope effect, and the subsequent effects on the reaction rate are studied. The reaction mechanism in acid medium assumes an electrophilic attack by the free acid RNHCl (CAT′) at the sulfur site in DMSO, forming a reaction intermediate which subsequently decomposes to dimethyl sulfone on hydrolysis. Formation of a cyclic complex between RNHCl and OsO₄ which interacts with the substrate in a slow step explains the observed results in alkaline medium. The simplification of the rate equation at higher alkali concentrations is attributed to a direct reaction between chloramine-T and the substrate.     

Carbocation-forming reactions in dimethyl sulfoxide

Mesylate derivatives of 3-aryl-3-hydroxy-beta-lactams and thiolactams react in DMSO-d(6) by first-order processes to give alcohol products. Substituent effect studies implicate carbocation intermediates (ion-pairs) that are captured by DMSO-d(6) to give transient oxosulfonium ions. Rapid reaction of the oxosulfonium ions with trace amounts of water leads to the alcohol product and regenerates DMSO-d(6). H(2)(17)O labeling studies show that (17)O is incorporated into the DMSO. The mesylate derivatives of endo- and exo-2-hydroxy-2-phenylbicyclo[2.2.1]heptan-3-one also react in DMSO-d(6) to give the alcohol products. Ion-pair intermediates that capture DMSO giving unstable oxosulfonium ions are again proposed. Exo-2-phenyl-endo-bicyclo[2.2.1]heptyl trifluoroacetate readily eliminates trifluoroacetic acid in DMSO-d(6) via a cationic mechanism involving loss of the endo-trifluoroacetate leaving group as well as an exo-hydrogen. The O-methyl oxime derivative of alpha-chloro-alpha,alpha-diphenylacetophenone reacts in DMSO-d(6) to give 1-methoxy-2,3-diphenylindole, a product derived from cyclization of a cationic intermediate. A common ion rate suppression provides further evidence for a cationic mechanism. The triflate derivative of pivaloin reacts by a cationic mechanism in DMSO-d(6) to give rearranged products. The rate is even faster than in highly ionizing solvents such as trifluoroethanol or trifluoroacetic acid. 1-Adamantyl mesylate reacts in DMSO-d(6) by a first-order process (Y(OMs) = -4.00) to give a long-lived oxosulfonium ion, 1-Ad-OS(CD(3))(2)(+), which can be characterized spectroscopically. This oxosulfonium ion reacts only slowly with water at elevated temperatures to give 1-adamantanol. DMSO is therefore a viable solvent for k(s), k(C), and k(Delta) cationic processes.     

An acidity scale of tetrafluoroborate salts of phosphonium and iron hydride compounds in [D2]dichloromethane

Equilibrium constants (K) for reactions between acids and the conjugate base forms of a number of phosphonium salts, [HPR3][BF4], and iron hydrides, [Fe(CO)3H(PR3)2][BF4], in CD(2)Cl(2) have been determined by means of 31P and 1H NMR spectroscopy at 20 degrees C. The anchor compound chosen for pK(CD(2)Cl(2)) determinations was [HPCy3][BF4] with a pK(CD(2)Cl(2)) value of 9.7, as assigned by literature convention (Cy: cyclohexyl). A continuous scale of pK(CD(2)Cl(2)) values covering the range from 9.7 to -3 was created and correlated with the DeltaH values reported by Angelici and co-workers and literature pK(a) values. The pK(CD(2)Cl(2)) values for 15 other hydride or dihydrogen complexes of the iron group elements and of diethyl ether were also placed on this scale. The crystal structures of [Fe(CO)3H(PCy(2)Ph)2][BF4] and [Fe(CO)3(PCy(2)Ph)2] revealed that the trans-oriented, bulky, unsymmetrical phosphane ligands distort the equatorial plane of the complexes. The acidity of iron carbonyl hydrides is an important feature of the reactions of iron hydrogenase enzymes.