Dimethyl Sulphoxide Water Research Articles

Trifluoromethyl ketone hydration. Substituent effects of amino-groups and the hydrating properties of aqueous dimethyl sulphoxide

The equilibrium constants for hydration of the 4-amino-, 4-methylamino-, and 4-dimethylamino-derivatives of ααα-trifluoroacetophenone have been determined in mixtures of dimethyl sulphoxide (DMSO) and D2O (or H2O) using 19F n.m.r. spectroscopy. The dimethylamino-compound follows the pattern observed earlier for the 4-methoxy-compound, i.e. in mixtures up to 80 mol % DMSO these compounds are more highly hydrated than in pure water. The extent of hydration of the amino- and methylamino-compounds, on the other hand, decreases steadily as the water content of the mixture is decreased. The difference in behaviour of the two groups of compounds is attributed to the presence of acidic protons in the unhydrated forms of the amino- and methylamino-compounds, which are able to form strong hydrogen bonds to DMSO. The results indicate the strong solvent dependence to be expected for σ+ substituent constants for the three kinds of amino-group. A sampling of other carbonyl compounds that undergo hydration revealed a considerable variation in the response of such compounds, equilibrium constants to changes in DMSO–water composition, with only one compound, 2-nitrobenzaldehyde, showing the sort of response that is shown by the 4-dimethylamino- and 4-methoxy-derivatives of trifluoroacetophenone.

Calculation of the phase diagram for the system water-dimethyl sulphoxide

Liquidus curves of the phase diagram for the system water-dimethyl sulphoxide (DMSO) have been calculated in such a way as to give a good fit to experimental data for the phase diagram. The calculation is based on the assumption of an equilibrium chemical reaction yielding DMSO.3 H2O, and on the relation for the excess Gibbs energy in a ternary system composed of the two starting components and their compound. The data for the temperature dependence of the difference in the heat capacities of the liquid and solid phases of the pure components in the supercooling region have been obtained by extrapolation of experimental data in the case of DMSO, and for water by adopting published data measured down to -40 °C and by estimating their further trend.

The Liquidus and Glass Transition Temperature of the Silver Nitrate—Dimethylsulphoxide—Water System

Article The Liquidus and Glass Transition Temperature of the Silver Nitrate—Dimethylsulphoxide—Water System was published on January 1, 1983 in the journal Zeitschrift für Physikalische Chemie (volume 136, issue 136).

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.

Water attack at an sp2 hybridized-carbon: the hydroxyl σ-complex of 4,6-dinitrobenzofuroxan in water–DMSO–tetramethylammonium chloride mixtures

The kinetics of formation and decomposition of the hydroxyl-σ adduct 2 derived from 4,6-dinitrobenzofuroxan 1 have been studied in various water – dimethylsulphoxide (DMSO) – tetramethylammonium chloride (I = 0.5 M) mixtures. At pH < 7, the formation of 2 occurs exclusively from water attack at the 7-carbon of 1. This process is strongly favored by DMSO: the first-order rate constant k1H2O changes from 1.9 × 10−2 s−1 in water to 1.33 s−1 in 90% DMSO. Taking into account the decrease in the water content of the solutions, and assuming that only one water molecule participates in the reaction, this increase in k1H2O reflects a 103-fold increase in the ability of a water molecule to act as a nucleophile. This interesting result compares well with previous data reported by Murto for the solvolysis of 2,4-dinitrofluorobenzene in the same solvent mixtures.

Nucleophilic attack on halogeno(phenyl)acetylenes by halide ions

Nucleophilic reactions between halogeno(phenyl)acetylenes and halide ions, ArCCX + Y–, where Ar = C6H5 or p-ClC6H4, X = Cl or Br, and Y = Cl or Br, have been examined. Halogen exchange of the Finkelstein type was observed for the first time in acetylene halides in anhydrous dimethyl sulphoxide when X = Br and Y = Cl. This exchange did not occur with other X–Y combinations. In the presence of up to 20% water in dimethyl sulphoxide, or under aqueous–organic phase-transfer catalytic conditions, nucleophilic addition (formally of HY) took place for all the X–Y combinations studied. In the additions, the nucleophile Y– invariably attacked the carbon to which the phenyl group was bound. The mode of HY addition was stereospecifically trans; accordingly, the resulting dihalogenostyrenes always had the (Z)-1,2-dihalogeno-configuration.

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.

Raman and infrared study on the effects of dimethylsulphoxide (DMSO) on water structure

AbstractRaman and infrared spectra of liquid dimethylsulphoxide (DMSO) and DMSO‐water mixtures in a wide range of concentrations are reported and discussed. It is found that changes in the vibrational spectra can be related to a gradual insertion of water molecules in the cluster structure of liquid DMSO. In the more dilute aqueous solutions a gradual lowering of the νs=0 stretching frequency is observed and this can be related to the cooperative character of DMSO–water interactions. The interpretation of the spectra is in agreement with the capacity of DMSO for ‘breaking’ the structure of water in the more concentrated aqueous solutions and ‘enhancing’ it in very dilute solutions.

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.

A correlation of substituent effects with the acidity of aromatic tetrazolic acids

The values of thermodynamic dissociation constants, Ka, have been determined for ortho-, meta-, and para-substituted 5-phenyltetrazoles (referred to as tetrazolic acids) and the effect of the nature of the substituent on the strength of the acids are discussed. The pKa values, determined in 50%(v/v) ethanol–water and in 75%(v/v) dimethyl sulphoxide–water are correlated with the substituent constants σm and σp, which are equal to 0.64 and 0.56 respectively for the tetrazolyl substituent. To evaluate the contribution of the field and resonance effects, the Ka values were correlated with the i…� and constants based on the Swain–Lupton equation. The correlation, accomplished by using a two-parameter linear regression, gave i…�= 1.17 and =–0.13.

Effects of N-methylation on the rates and equilibrium constants for protonation of meso-tetraphenylporphyrin in 98%(v/v) dimethyl sulphoxide–water

Equilibrium constants for the first and second protonations of N-methyl-meso-tetraphenylporphyrin have been measured in 90% and 98%(v/v) Me2SO–H2O. The interconversion of the mono- and di-protonated forms of N-methyl-meso-tetrakis-(p-methoxyphenyl)porphyrin occurs slowly and the rate coefficient for thermodynamically favourable protonation of the monoprotonated form by hydronium ion has a value of 4.3 × 105 I mol–1 s–1 in 98%(v/v) Me2SO–H2O. The results are compared with kinetic and equilibrium results for meso-tetraphenyl- and meso-tetrakis-(p-methoxyphenyl)-porphyrins for which only the overall equilibrium between the porphyrin and diprotonated species could be studied since the monoprotonated species were undetectable in 90% and 98%(v/v) Me2SO–H2O. Possible reasons for the differences in behaviour are discussed.

Effect of reaction medium on the radical polymerization and copolymerization of potassium and sodium p-styrenesulphonate

The kinetics of the homogeneous free radical polymerization of potassium p-styrenesulphonate and sodium p-styrenesulphonate (SSS) in water-salt, water-dioxane, water-dimethyl sulphoxide (DMSO), DMSO—dioxane mixtures and copolymerization of SSS with acrylamide in water-salt and water-DMSO mixtures have been investigated. The overall rate of the process, the kinetic orders with respect to monomer and initiator, overall activation energy and also the properties of the resulting polymers (molecular weight, copolymer composition and compositional inhomogeneity) depend on the nature of the reaction medium. It is mainly connected with the influence of ionic strength (due to varying ionogenic monomer concentration, addition of salts and also the change of the conversion degree) and with the influence of the polarity of solvent on the rate constants for propagation and termination. The chemical and physical characteristic of the reaction mainly influence parameters of the electrostatic interactions in the system “macroradical-counterions-anions of monomer”. This leads to conformational variation of polymer chains and influences the reactivities of growing macroradicals and ionogenic monomers in polymerization and copolymerization. Data on conductivity and viscometric measurements confirmed the dependence of the conformation of polymer and copolymer macromolecules upon the composition of the medium.

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.

Acid-catalysed solvolysis of 2-diazo-4′-methoxy- and 2-diazo-2-phenyl-acetophenone in aqueous–organic mixtures

Rate constants for the hydrolysis of 2-diazo-4′-methoxy- and 2-diazo-2-phenyl-acetophenone are reported together with H0 acidity functions in dimethyl sulphoxide–water, ethanol–water, and methanol–water mixtures containing dilute perchloric acid. The hydrolysis of 2-diazo-2-phenylacetophenone has been studied in ‘neutral’ dioxan–water mixtures and in dioxan–water mixtures containing 0.1 M-hydrochloric or -perchloric acid. Results of some kinetic isotope effect studies are reported. Graphs of log (observed rate constant) against H0 are linear for reactions in perchloric acid solutions of fixed solvent composition. The effects of changing the solvent composition in the presence of 0.1 M-acid are correlated by plotting H0+ log (observed rate constant) against log (activity of water). 2-Diazo-4′-methoxyacetophenone appears to hydrolyse by an A-1 mechanism in all the solvent mixtures studied. The kinetic behaviour of 2-diazo-2-phenylacetophenone is less consistent: in some conditions an A-2 route seems to be preferred; in others an A-SE2 route seems more likely; in some cases the reaction is not first order.

Solvent dependence of kinetic hydrogen isotope effects for simple proton transfer

Kinetic hydrogen isotope effects for some simple proton transfer reactions, involving 2-nitropropane, nitroethane, and ethyl 2-methvlacetoacetate as substrates, have been measured in a variety of solvent mixtures (dimethyl sulphoxide–water, acetonitrile–water. and 2,2,2-trifluoroethanol–water). Both rates and isotope effects vary considerably as the solvent composition is altered, but they show no correlation with the effect of the solvent on the overall free energy changes for the reactions. The results are discussed in relation to current theories of isotope effects.

Rates of proton transfer, acid dissociation constants, and the strengths of intramolecular hydrogen bonds in 8-methoxy-NN-dimethyl-1-naphthylammonium ion and 8-hydroxy-NN-dimethyl-1-naphthylamine

The rate coefficients for proton transfer from 8-hydroxy-NN-dimethyl-1-naphthylamine in 80%(v/v) dimethyl sulphoxide–water and from 8-methoxy-NN-dimethyl-1-naphthylammonium ion in aqueous solution are respectively 104 fold and 20–50 fold lower than expected for normal proton transfers from a hydroxy- and protonated amino-group. The low rates are due to intramolecular hydrogen bonds in the acids and by comparison with results for protonated 1,8-bis(dimethylamino)naphthalene, the rates show that in this series of peri-substituted naphthalenes the order of hydrogen bond strengths is [graphic omitted]–H ⋯ O < O–H ⋯ N < [graphic omitted]–H ⋯ N. The intramolecular hydrogen bonds also account for the unusual acidities: 8-methoxy-NN-dimethyl-1-naphthylammonium ion (pK 7.75) is a weaker acid by three pK units than NN-dimethyl-1-naphthylammonium ion and 8-hydroxy-NN-dimethyl-1-naphthylamine (pK ca. 14.9) is six pK units weaker than 1-naphthol.

Kinetic and equilibrium studies of the protonation of meso-tetraphenylporphyrin in dimethyl sulphoxide–water

The equilibrium between meso-tetraphenylporphyrin (B) and its diprotonated form (BH22+) has been studied spectrophotometrically in 98, 90, and 80% Me2SO–H2O (v/v). Visible spectra of solutions of the porphyrin containing varying concentrations of hydrochloric acid show good isosbestic points. The equilibrium involves the free base and the diprotonated species; the monoprotonated porphyrin (BH+) is not present in sufficiently high concentrations to be detected. The position of equilibrium and the rates of equilibration between B and BH22+ have been measured in 95, 90, and 85% Me2SO–H2O (v/v). The reaction is slow, with relaxation times (measured by the temperature-jump method) in the range 40–5 000 µs. Values of the rate coefficient for proton removal by water from BH22+ to give BH+ were obtained for each solvent mixture from the acid dependence of the reciprocal relaxation time. In comparison with other proton transfers from nitrogen acids, proton transfer from the diprotonated form of meso-tetraphenylporphyrin is exceptionally slow. This may arise because the reaction is strongly disfavoured thermodynamically; other possible factors are discussed.

Rates of proton transfer from protonated 1,8-bis(dimethylamino)- and 1,8-bis(diethylamino)-naphthalene to hydroxide ion in 20% and 30%(v/v) dimethyl sulphoxide–water

The conjugate acids of 1,8-bis(dimethylamino) naphthalene and 1,8-bis(diethylamino) naphthalene are intramolecularly hydrogen-bonded, and proton transfers to hydroxide ion in 30%(v/v) dimethyl sulphoxide–water occur slowly, with rate coefficients (kOH–) 6.1 ± 105 and 1.6 ± 104 I mol–1 s–1, respectively. Substitution of ethyl groups for methyl groups in 1,8-bis(dimethylamino)naphthalene has a larger effect on the rate of proton transfer than on the equilibrium constant, and this unusual observation is considered in terms of a two-step mechanism for proton removal from the protonated amines.