Dimethyl Sulphoxide Water Mixtures Research Articles

Preferential solvation and the composition of the solvation shell of (dimethyl sulphoxide)penta-amminechromium(III) ion in dimethyl sulphoxide–water mixtures

The number of solvent molecules in the solvation shell of the title complex ion has been found to be 10, the stepwise equilibrium constants for the replacement of the 10 water molecules by 10 dimethyl sulphoxide molecules have been obtained, and the free energy increment per replacement step has been found to be ∼+1.42 kJ mol–1.

The stabilities of Meisenheimer complexes. Part 40. A kinetic study of the reaction of 1-chloro-2,4-dinitrobenzene with sulphite ions in water–dimethyl sulphoxide mixtures

Kinetic and equilibrium data are reported for the reactions of 1-chloro-2,4-dinitrobenzene with sulphite ions in dimethyl sulphoxide–water mixtures. Attack at the unsubstituted 5-position yields an observable σ-adduct and is shown to be more rapid by a factor of ca. 12 than attack at the 1-position. The latter process which yields the substitution product is likely to involve intermolecular attack of sulphite on the substrate rather than intramolecular re-arrangement of the 5-adduct.

Initial state and transition state contributions to solvent effects on rate constants for racemisation and dissociation of the [Fe(phen)3]2+ cation in DMSO-water mixtures

Rate constants for racemisation and dissociation of the tris(1,10-phenanthroline)iron(II) cation, and solubilities of its picrate, are reported for dimethyl sulphoxide-water mixtures (0 to 40% by vol DMSO) at 298.2 K. The observed solvent effects on reactivity are analysed in terms of initial state and transition state contributions, and the pattern established compared with patterns for methanol- and acetone-water mixtures. In all cases the hydrophobic periphery of the ligand is dominant. Rate constants are also reported for racemisation and dissociation of the analogous complex [Fe(sb)3]2+, where sb = the Schiff base from 2-benzoylpyridine andp-toluidine, in aqueous methanol.

The reaction of nickel(II) with 2,2?-bipyridyl in methanol- and in dimethyl sulphoxide-water mixtures: Solvent effects on reactivity

Enthalpies of solution (298 K) are reported for NiCl2 · 6H2O, CoCl2 · 6H2O, and FeCl2 · 4H2O in aqueous methanol (0–40% methanol) and for NiCl2 · 6H2O, 2,2′-bipyridyl, and water in aqueous dimethyl sulphoxide (0–60% DMSO). Solubilities (298 K) of 2,2′-bipyridyl are reported for aqueous dimethyl sulphoxide (0–60% DMSO). From these, from appropriate published thermodynamic data, and from published rate constants and activation enthalpies, we have analysed solvent effects on reactivities (μ and H) into initial state and transition state contributions (the latter are in fact composite ion-association and interchange quantities). In all systems examined the observed kinetic trends represent small differences between large and almost identical solvent effects on the respective initial and transition states.

Calorimetric study of the ionization process for 2,4-dinitrophenol in water—dimethylsulphoxide mixtures at 25°C

The ionization and solution enthalpies of 2,4-dinitrophenol were measured calorimetrically at 25°C in water—DMSO mixtures ranging from 0.1 to 0.8 mole fraction of DMSO. The greater acidity of 2,4-dinitrophenol with respect to 2,5-dinitrophenol is explained on the basis of the observation that in the anion the π-withdrawing resonance effect of the para nitro group stabilizes the benzene ring while in the undissociated molecule the contrary is true.

Complete thermodynamic analysis of the ionization of anisic acid in water—dimethylsulphoxide mixtures at 25°C

The ionization and solution enthalpies of para-methoxybenzoic (anisic) acid have been measured in H 2O—DMSO mixtures. In the same solutions, the Δ G 0 values for the ionization process have been determined by potentiometric measurements. A study of the enthalpic and entropic contributions to substituent and reaction constant effects, and the proton transfer process from the methoxy derivative to benzoic acid, compared with the same process in the gaseous phase, is also presented.

Enthalpies of solution of lanthanum, gadolinium and ytterbium trichlorides in binary aqueous solvent mixtures

Enthalpies of solution are reported for anhydrous lanthanum trichloride in methanol-, ethanol-, t-butyl alcohol-, and dimethyl sulphoxidewater mixtures, for anhydrous gadolinium trichloride in methanolwater mixtures, and for ytterbium trichloride in methanol- and dimethyl sulphoxidewater mixtures, at 298.2 K. The estimation of enthalpies of transfer of lanthanide(III) cations into these binary aqueous solvent mixtures is discussed.

ORTHO effects of chloro- and nitrobenzoic acids in water—dimethylsulphoxide mixtures at 25° C

The dissociation of ortho-chloro- and nitro-benzoic acids in water—DMSO mixtures (0.0 + 0.8 DMSO mole fraction) was studied by means of a linear combination of the ordinary polar, proximity polar, and steric effects. Enthalpic and entropic contributions to substituent effects for the ortho-derivatives were also examined. The dissociation of the ortho-chloro-derivatives appear to be mostly anion-controlled. However, for the ortho-nitro-derivatives, the steric inhibition of solvation on the undissociated molecules may also be involved in controlling the course of the reaction.

Enthalpic and entropic contributions to substituent effects for the ionization of meta- and para-nitrobenzoic acids in water-dimethylsulphoxide mixtures at 25°C

Enthalpic and entropic contributions to substituent effects for the ionization of m-and p-nitrobenzoic acids are examined, ranging from pure water to 0.8 mole fraction DMSO. The effect of the medium on the substituent and reaction constants is explained in terms of solute—solvent interactions. No structure-breaking effect was found.

Solubilities of Sodium Chloride and Ion-Solvent Interaction in Dimethyl Sulphoxide—Water Mixtures at 25°

Solubilities of Sodium Chloride and Ion-Solvent Interaction in Dimethyl Sulphoxide—Water Mixtures at 25°

Radiolytic reduction of ceric ions in water DMSO mixtures and radioprotection

It is convenient to classify mechanisms of radioproteetion into those that involve fast radiation chemical processes and those in which the protection is the result of changes in the cell biochemistry. In the former, the added protectors have two principal effects: OH scavenging which reduces the radiosensitised damage and fast chemical repair processes involving hydrogen donation from the protector to the target radical. Typical of the first type of protector is dimethyl sulphoxide(DMSO)1 because it is known to be a good OH scavenger (kOH+DMSO =5×109 mol−1 s−1. (ref. 2). We have attempted to establish the redox properties of the OH radical adduct3 as well as those of H2O2 or H and HO2 radicals in water–DMSO mixtures. To this end we added to the solutions containing 0.5 M H2SO4, cerie ions at concentrations varying from 2.5 × 10−3 to 5 × 10−2 M. The Ce4+ reduction yield was determined as a function of the DMSO content in the solution, by irradiating the mixture with γ rays, in the presence or absence of air. The details of the experimental procedure will be given elsewhere. We report here that the yields (G) are independent of the Ce4+ concentration in the range studied and of the presence or absence of air, and depend only on the DMSO concentration.

Control of intramolecular γ-alkylation vs.α-alkylation of an αβ-unsaturated ketone: an unusual solvent effect

Most base–solvent combinations convert (2) into (3); γ-alkylation to yield (5) is effected by sodium hydroxide in dimethyl sulphoxide–water mixtures in which the water content is critical.

Reactions of low-spin iron(II) complexes with hydroxide ion in aqueous methanol: the effect of ligand on rates of reaction

Rate laws and rate constants are reported for reactions of several low-spin iron(II) complexes with hydroxide ion in methanol-water solutions. The dependence of the form of the rate law and of reactivity on ligand type and on substituent nature is discussed. The pattern of reactivity for a range of compounds with hydroxide ion in methanol-water mixtures is compared with the reactivity pattern for analogous reactions in dimethyl sulphoxide-water mixtures.

Hydrogen isotope exchange in the aldehyde group during the reduction of benzaldehyde by tritiated sodium borohydride (tetrahydridoborate)

The reduction of benzaldehyde by tritiated sodium tetrahydridoborate in dimethyl sulphoxide and dimethyl sulphoxide–water mixtures as solvents is accompanied by the incorporation of tritium into the aldehyde group of unchanged benzaldehyde. The occurrence of the exchange implies that the hydride-transfer step of the reduction is reversible. As it is improbable that there is reversibility after the formation of a stable boron–oxygen bond, it is concluded that the hydride-transfer step precedes the step in which the boron–oxygen bond is formed. However, attempts to detect the implied intermediate borane in dimethyl sulphoxide solution by trapping with amines had proved negative. It follows that borane is destroyed by reaction with the other product of the first reaction step (the benzyl oxide ion) more effectively than it can react with an amine. Since the reaction of borane with a tertiary alkylamine is likely to be very rapid, the reactions between borane and benzyl oxide ion (leading either back to the starting materials with hydrogen exchange or, predominantly, to an alkoxyhydridoborate species) are considered to occur competitively as cage reactions before the primary reaction products have diffused apart.The exchange reaction exhibits kinetic complications which are attributed to a more rapid hydrogen exchange between benzaldehyde and the reaction product sodium tetrakisbenzyloxyborate (which is shown to take place) and to the instability of this product in the media employed. It is suggested that the high basicity of the reaction solutions is due to the presence of some sodium benzyl oxide in equilibrium with sodium tetrakisbenzyloxyborate, leading to the formation of dimsyl ions.

The isomerization of ammonium cyanates. II. The kinetics of isomerization of ammonium and alkylammonium cyanates in dimethyl sulphoxide-water mixtures

The kinetics of the isomerizations of ammonium, methylammonium and ethylammonium cyanates to urea, methylurea and ethylurea have been studied in aqueous dimethyl sulphoxide over the range 0-100% dimethyl sulphoxide. Side reactions occur at all solvent compositions and urea formation accounts for only between 65% and 90% of products. The side reaction in water produces carbonate and in dimethyl sulphoxide biuret or alkyl-substituted biurets. The proportion of each of these products in solvent mixtures has not been determined.

KINETICS, MEDIUM, AND DEUTERIUM ISOTOPE EFFECTS IN THE ALKALINE DECOMPOSITION OF QUATERNARY PHOSPHONIUM SALTS III1Tetraphenylphosphonium Chloride in Dimethylsulphoxide-Water Mixtures

Abstract The reaction between tetraphenylphosphonium chloride and hydroxide or deuteroxide anions was studied kinetically in a series of dimethylsulphoxide-water mixtures at several temperatures. The rate is first-order in the phosphonium cation and second-order in the hydroxide or deuteroxide anions. The reaction shows a dramatic increase in rate, up to about 1010 times, as the DMSO content is increased. The rate enhancement is attributed to a considerable drop in activation energy affected not only through an increased desolvation of reactant anions, but also through an increase in solvation of the transition state, brought about by gradual addition of DMSO. The kinetic solvent deuterium isotope effect in 60% DMSO-40% D2O is strongly dependent on temperature. The rate constant in the latter solvent mixture is represented by k i = 11.9 e −12700/RT l 2 mole−2 sec−1 as compared to k i = 19.0 e −22500/RT l 2 mole−2 sec−1 in the corresponding 60% DMSO-H2O mixture. The thermodynamic parameters of activation s...

Determination of gibbs free energy of transfer for alkali metal chlorides from water to water dimethylsulphoxide mixtures using cationic glass electrodes—a test for the method

Determination of gibbs free energy of transfer for alkali metal chlorides from water to water dimethylsulphoxide mixtures using cationic glass electrodes—a test for the method

The acidities of weak acids. Part IV. Some methyl styryl ketones

A series of ring-substituted methyl styryl ketones (XC6H4·CH:CH·CO·CH3) have been synthesised and their acidities measured at 298.2 K using solutions of tetramethylammonium hydroxide (0.011 M) in dimethyl sulphoxide–water mixtures. In most cases the rates of detritiation in aqueous hydroxide ion solutions have also been measured. The results show that these compounds obey the same pKa–lgkTOH– relationship as was established for the structurally similar acetophenones.

Transition state enthalpies of transfer in aqueous dimethyl sulphoxide solutions. The hydroxide-catalysed racemisation ofD-α-methyl-α-phenylacetophenone

Enthalpies of solution of D-α-methyl-α-phenylacetophenone in a series of dimethyl sulphoxide–water mixtures have been measured. Taken in conjunction with the enthalpies of transfer of the hydroxide ion from a 27.8 mol% dimethyl sulphoxide–water mixture to solutions of higher dimethyl sulphoxide concentrations, and the previously published enthalpies of activation for the racemisation of the ketone, transition state enthalpies of transfer have been calculated. The results show that the increase in rate accompanying the increase in dimethyl sulphoxide concentration can be mainly accounted for by desolvation of the hydroxide ion but that desolvation of the transition state makes the increase less than it would otherwise be.

Enthalpies of transfer involving ionic transition states : the redundance of extrathermodynamic assumptions

It is pointed out that the calculation of transition state enthalpies of transfer for reactions involving ions does not necessitate the estimation of thermodynamic quantities for single ions. The procedure is illustrated by data on the reaction between ethyl acetate and sodium hydroxide in water–dimethyl sulphoxide mixtures.