Dimethyl Sulphoxide Water Research Articles

Base-catalysed mutarotation of glucose in dimethylformamide and dimethyl sulphoxide

The rate of mutarotation of glucose has been measured in pure dimethylformamide and dimethyl sulphoxide with substituted benzoate ions as catalysts, and in 80 vol % dimethyl sulphoxide-water with acetate and chloroacetate as catalysts. Unlike many other base–catalysed reactions in these solvents, the rates show no subtantial increase over those observed in water. This is interpreted in terms of a strong involvement of water with the transition state in aqueous media, in accordance with earlier suggestions concerning the mechanism of related reactions such as the addition of water and alcohols to carbonyl compounds. In combination with previously reported pK values in the appropriate solvents, the results show that there is a good correlation of the catalytic effect of the anion bases with their basic strengths. The observed Bronsted coefficients are slightly higher (β= 0.6 in dimethylformamide and dimethyl sulphoxide) than in water (β= 0.4).

Reduction of carbonyl compounds by sodium borohydride (tetrahydridoborate) in water, dimethyl sulphoxide, and their mixtures as solvents: products and kinetics

Rate measurements are reported for the reduction of acetone pivalaldehyde, and benzaldehyde by sodium and tetramethylammonium tetrahydridoborates in dimethyl–sulphoxide–water systems, some containing a low concentration of sodium hydroxide to impede the hydrolysis of tetrahydridoborate. The reactions obey second-order kinetics. The rate constants decrease as the water content of the solvent is reduced but, with the most reactive substrate (benzaldehyde), the reduction is still detectable even in a solvent not containing any added water. Evidence has been obtained that the reduction product of benzaldehyde in dimethyl sulphoxide solution is sodium tetrakisbenzyloxyborate, which is readily hydrolysed to benzyl alcohol. A condensation product of benzaldehyde and dimethyl sulphoxide (2-methylsulphinyl-1-phenylethanol) has been isolated as a by-product. Attempts to trap borane during the reduction gave negative results.

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.

Ion solvation studied by NMR and electrochemical methods

Electrochemical and NMR experiments with solutions of silver salts in mixtures of water—acetonitrile, water—dimethylsulphoxide, and methanol—dimethylsulphoxide have been compared and discussed in terms of ion solvation and solvent-solvent interactions. The solvation of aluminum(III) in mixtures of N,N-dimethylformamide, dimethylsulphoxide, and nitromethane depends also on solvent-solvent interactions, as 1H- and 27Al-NMR measurements show.

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

Heterocyclic synthesis from o-halogeno-acids. Part III. Synthesis of 2-methylindole-4-carboxylic acid and related compounds and of some derivatives of 3-phenylisoquinolin-1(2H)-one

Condensation of 2-bromo-3-nitrobenzoic acid with acetylacetone in the presence of copper(II) acetate and ethanolic sodium ethoxide gives 2-acetylacetonyl-3-nitrobenzoic acid. Deacetylation with water–dimethyl sulphoxide at 170 °C yields 3-methyl-5-nitroisocoumarin, which is converted by catalytic hydrogenation and alkaline hydrolysis into 2-methylindole-4-carboxylic acid. Similar condensation and reduction reactions yield related compounds including dimethyl 2-methylindole-3,4-dicarboxylate. Tricyclic products are obtained by heating o-phenacylbenzoic acid with 2-amino-1-phenylethanol, ethane-1,2-diamine, and o-phenylenediamine. o-Phenacylbenzoic acid is also converted into 2-substituted 3-phenylisoquinolin-1(2H)-ones, which are cyclised to form dibenzo[a,g]-quinolizin-8-one derivatives and/or oxazolo[2,3-a]isoquinolinylium salts.

Kinetics and isotope effects in proton transfers from 3-bromo- and 3-nitro-(+)-camphor

The rates of mutarotation of 3-bromo-(+)-camphor and 3-bromo-3-deuterio-(+)-camphor have been measured in solutions of sodium hydroxide in 15–70% v/v dimethyl sulphoxide–water, and in 20 and 45% w/w dioxan–water. The rate increases sharply with dimethyl sulphoxide content, and the primary hydrogen isotope effect shows indications of a maximum at about 40% dimethyl sulphoxide. The same reaction was studied in glycine buffer solutions in 15% dimethyl sulphoxide and in the two dioxan–water mixtures. There is clear evidence for general base catalysis by the glycine anion, compared with which the effect of hydroxide ions is abnormally small.The rates of bromination of 3-nitro-(+)-camphor and of 3-deuterio-3-nitro-(+)-camphor were measured in a variety of aqueous buffer solutions. The reaction is of zero order with respect to bromine and is catalysed by the basic buffer components. The pK of 3-nitro-(+)-camphor was found to be 3.54, and the isotope effect exhibits a marked maximum when the pK of the buffer acid is close to this value. The reactions of both isotopic species conform fairly well to Bronsted relations, but it is pointed out that the existence of a maximum in KH/KD must imply a deviation from a linear relation for at least one of the isotopic species, and the experimental results lend some support to this view.

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.

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.

Conductance of acids in dimethylsulphoxide—I: Conductance of hydrochloric acid in DMSO—water mixtures at 25°C

Conductance measurements at 25°C are reported for dilute solutions of hydrochloric acid in dimethylsulphoxide and in dimethylsulphoxide—water mixtures containing up to 15% by weight of water. The results are analysed in terms of full Fuoss—Hsia conductance equation. Association constants decrease as the water content is increased whereas Λ α values pass through a minimum at about 11% water.

Water transport in aqueous organic solvents. Dimethyl sulphoxide + water + hydrochloric acid at 25°C

An e.m.f. method has been used to determine, (a) the molar transport number, or Washburn number, tw, of water in dimethyl sulphoxide + water mixtures containing hydrochloric acid and (b) the transport numbers of hydrochloric acid in these solvent mixtures. Within the composition range studied [up to 40 %(w/w) dimethyl sulphoxide], tw shows a pronounced variation with solvent composition, passing through a maximum at 10–20 % dimethyl sulphoxide. These features are discussed in terms of the effects of solvent structure and ion-solvent interactions on the transport of water by the ions.

Rates of proton transfer for meso-tetraphenylporphyrin in 90% dimethyl sulphoxide–water (v/v)

The rate of ionisation of the diprotonated form of meso-tetraphenylporphyrin (BH22+)to the mono-protonated form (BH+)has been measured by a tempera-ture-jump study of the equilibration between B and BH22+ and is unusually slow.

The substituent dependence of the primary deuterium kinetic isotope effect in elimination from phenethyl bromides and dimethyl(phenethyl)-sulphonium bromides in 50·2 mole % dimethyl sulphoxide–water

Primary deuterium kinetic isotope effects (K2H/K2D) have been determined for 1,2-elimination from a series of substituted phenethyl bromides and dimethyl(phenethyl)sulphonium bromides in 50·2 mole % Me2SO–H2O. A maximum in the K2H/K2D ratio was observed for the phenethyl bromides but the existence of a maximum could not be determined for the dimethyl(phenethyl)sulphonium bromides. Some evidence for proton tunnelling is presented for the p-methoxy-compounds. Hammett ρ values were determined and the value was larger for the poorer leaving group.

The acidities of weak acids. Part I. A new method for determining pKavalues in the range 12–24

A kinetic method of determining weak acidities, based on following the rates of detritation of a ‘standard’ carbon acid in a series of dimethyl sulphoxide–water solutions containing a fixed concentration of hydroxide ions, both in the presence and absence of a second acid, is reported. The method, which has been established by redetermining the acidities of some diphenylamine and aniline-type indicators is well suited to studying acids (pKa values in the range 12–24) whose absorption spectra do not undergo significant change on ionisation.

Interaction of acridine orange and amylose in a binary liquid system dimethyl sulphoxide-water

Interaction of acridine orange and amylose in a binary liquid system dimethyl sulphoxide-water

Sorption of potassium on synthetic 4A zeolite from water and water-dimethyl sulphoxide (DMSO) mixtures

The exchange of Na + and K + ions on 4A zeolite in water and water-DMSO mixtures has been studied at various temperatures and at constant ionic strength (0·10 M). Thermodynamic values for the complete exchange process were calculated. The exchange process is of a complex character. At lower potassium loadings ( n K z < 0·3) K + ion is preferred to Na + ion, and at higher loadings ( n K z >0·3) Na + ion is preferred. With earlier data for the Na +−Li + exchange, the selectivity sequence Na> K>Li was found in both media for the complete process, and the sequence K>Na>Li for the process at n K,Li z < 0·3. Activity coefficients and activities of cations in the zeolite were computed as a function of zeolite composition.

Base cleavage of trimethylsilyl-1,2-dihydrobenzocyclobutenes, and its significance for the acidities of the 1-, 3-, and 4-positions of 1,2-dihydrobenzocyclobutene (“benzocyclobutene”).

The rates of cleavage of the 1-, 3-, and 4-trimethylsilyl derivatives of 1,2-dihydrobenzocyclobutene (“benzocyclobutene”) (I) by potassium hydroxide in dimethyl sulphoxide—water have been measured spectrophotometrically. The 3-derivative is 10.6 times as reactive as its 4-isomer, and 8.5 times as reactive as its closest analogue 1,2-dimethyl-3-trimethylsilylbenzene. The results are consistent with enhanced electronegativity of the 3-carbon atom [and thus enhanced acidity of the 3-position of (I)], which is associated with the effect of the ring-strain on the hybridization of the orbitals of the atoms of the 4-membered ring. The reactivity of the 1-derivative is much greater than that of its 3- and 4-isomers, and rather similar to that of its analogue, α-(trimethylsilyl)ethylbenzene; any enhancement of the electronegativity of the 1-carbon atom appears to be balanced out by the less effective delocalization of a lone-pair from the 1-carbon into the aromatic ring. In the strongly-basic medium used (0.05 M KOH in dimethyl sulphoxide containing 3 wt. % of water), phenyltrimethylsilane is some 9 times as reactive as its tin analogue; this unusual order of reactivity may be associated with a smaller contribution from proton-transfer to the separating carbon atom in a medium of low hydroxylic content.

Evaluation of 1-fluoro-2-nitro-4-trimethylammoniobenzene iodide, a protein-solubilizing reagent.

The new protein reagent 1-fluoro-2-nitro-4-trimethylammoniobenzene iodide reacts with model amino acids to give derivatives that are very stable to hydrolysis. In a dimethyl sulphoxide-water medium it reacts rapidly (3h) with bovine insulin, and substitution occurs quantitatively at the N-terminal amino groups and at the in-amino groups of lysine residues. Two of the four tyrosine residues react, and it is assumed that these are the exposed groups leaving the buried groups unattacked. Unlike 1-fluoro-2,4-dinitrobenzene and related reagents, it imparts hydrophilic properties to the protein derivative, thus facilitating structural and other studies on the derivative. Circular-dichroism spectra of the modified insulin suggest that no conformational changes have occurred during reaction. These spectra also reveal the presence of an extrinsic Cotton effect at 410nm.

Sodium-lithium exchange on synthetic zeolite 4A in water-dimethyl sulphoxide (DMSO) mixtures

Sodium-lithium exchange on synthetic 4A zeolite from 0·1 and 0·01 isomolal solutions of NaCl + LiCl in water-DMSO mixtures has been investigated. Ion-exchange isotherms are identical for the solutions of the two ionic strengths. They are of a complex type, indicating two successive processes. 4A zeolite shows a higher selectivity for sodium, which increases with increasing DMSO content of the mixture. Thermodynamic values ΔG 0, ΔH 0 and ΔS 0 were obtained. Between 5 and 45° the exchange is practically temperature independent in mixtures with more than 20 wt.% DMSO. The data are compared with those of water and water-dioxane systems obtained earlier, and are discussed with respect to the dielectric constant and solvating ability of the solvents.