Methanol Dimethyl Sulphoxide Research Articles

Determination of quercetin in human plasma by HPLC with spectrophotometric or electrochemical detection.

A reversed-phase high-performance liquid chromatographic method for the determination of quercetin in human plasma following intravenous infusion is described. Quercetin in plasma was extracted with methanol-dimethyl sulphoxide (4:1 v/v) and separated on a C18 Hypersil-BDS column with 44% (v/v) methanol in 0.1 M ammonium acetate (pH 5.15) containing 0.27 mM EDTA as the mobile phase. The drug was detected specifically and sensitively at its absorption maximum of 375 nm, or electrochemically, with a detection limit of 80 ng/mL and 2 ng/mL, respectively.

A study of trapping levels in some red mercuric iodide single crystals for nuclear radiation detection

Photon-stimulated currents (PSC) and thermally stimulated currents (TSC) have been measured in red mercuric iodide ( alpha -Hgl2) single crystals grown in our laboratory from tetrahydrofurane- alpha -Hgl2 saturated solution, dimethyl sulphoxide-methanol- alpha -Hgl2 saturated solution and from a polymer-controlled vapour phase. PSC measurements helped in determining uniquely the activation energies and nature (electron or hole) of different trapping levels in these crystals. Subsequently, by a comparative study of TSC and PSC measurements, the capture cross sections have been determined uniquely. Finally, after estimating the trap densities, an attempt has been made to predict the influence of different trapping levels on the performance of the detectors fabricated out of the three types of crystal.

Reactions in strongly basic media. Part 10. Base-catalysed isomerisation of Z- to E-substituted chalcones

The rate coefficients for the methoxide-catalysed isomerisation of substituted (Z)-chalcones have been measured in methanolic dimethyl sulphoxide (DMSO) at 30.0 °C, as well as for (Z)-chalcone at several temperatures. The reactions are first order in substrate and base. Further, log k1 for the reaction of (Z)-chalcone and (Z)-4-nitrochalcone correlate with an acidity function, HR–, having slopes equal to 0.53 and 0.45, respectively. The effect of substitution has been assessed using the Hammett equation, with ρ equal to 1.99 for the β-phenyl group and 1.93 for the benzoyl group. For the (Z)-chalcone, the enthalpy and entropy of activation are 14.2 kcal mol–1 and –14 cal mol–1 K–1, respectively, and the kinetic solvent isotope effect, k2MeOD/k2MeOH, is ca. 2.0. The rate coefficients for the amine-catalysed isomerisation of (Z)-chalcone and (Z)-4-nitrochalcone in DMSO have been measured at 30.0 °C. The amino bases are a series of secondary aliphatic amines and the Bronsted coefficients, β, are given as 0.39 and 0.38, respectively. The isomerisation is considered to proceed by rate-determining attack of the base at the β-carbon of the (Z)-chalcone to form a carbanion. The ‘cis’-conformer of the carbanion then rotates to form the ‘trans’-conformer, which eliminates the base to give the (E)-chalcone.

ChemInform Abstract: Reactions of Carbonyl Compounds in Basic Solutions. Part 11. The Baker‐Venkataraman Rearrangement.

AbstractThe rearrangements of 2‐acetylphenyl benzoate (I) (R: ‐H) catalysed by the phenols (II) and KOtBu, of the derivatives (I) (R: ≠H) catalysed by (II) (R: ‐Me) and KOtBu, and of (I) (R: ‐H), (IV), and (V) in the temp. range 18.4‐40.2 °C catalysed by (II) (R: ‐Me) and KOtBu have been studied kinetically.

ChemInform Abstract: Reactions of Carbonyl Compounds in Basic Solutions. Part 10. Methoxide‐Catalysed Cyclisation of Methyl‐2‐Acylbenzoates and 8‐Acyl‐1‐naphthoates

The detailed mechanism of the methoxide-catalysed rearrangement of both normal and pseudo methyl o-acylbenzoates and 8-acyl-1-naphthoates to form indane-1,3-diones and phenalene-1,3-diones, respectively, has been studied. Rate–acidity function correlations for the reactions in methanolic dimethyl sulphoxide give linear relations. The kinetic isotope effects have been observed with kH/kD equal to 0.7–0.9 and 5–7 for methyl o-acetylbenzoate and normal methyl 8-acetyl-1-naphthoate, respectively. The effect of substituents and ring–chain tautomerism on the rates has been considered. For the o-acylbenzoates the initial state is the ring-chain tautomeric equilibrium mixture and the rate-determining step is the intramolecular attack of the anion of the normal ester. For normal 8-acyl-1-naphthoates the rate-determining step is the ionisation of the normal esters; for the corresponding pseudo esters, the rate-determining step is the isomerisation of the psuedo to the normal ester.

Isotachophoresis in mixed solvents consisting of water, methanol and dimethyl sulphoxide : I. The acid—base and migration behaviour of substituted benzenecarboxylic acids

The acid—base properties of 30 neutral acids (benzenecarboxylic acids were investigated in methanol—water and dimethyl sulphoxide—methanol—water. The results of the estimation of the apparent p K values are discussed on the basis of the concept of transfer activity coefficient and interpreted by anion solvation effects. Different changes in the apparent p K values in the solvents were utilized to enhance the selectivity characteristics of isotachophoresis. For this purpose, a number of analytes were characterized by their relative step heights in two aqueous electrolyte systems with different pH values of the leading electrolyte. The corresponding properties of the analytes were also determined in systems with equal apparent pH values but different solvent compositions. The similarity of two aqueous two mixed aqueous—organic electrolyte systems was quantified by numerical taxonomy, using the effective ionic mobilities as parameters. The mobilities were determined from the relative step heights. As a result, the systems with (apparent) pH values of 5.7 and dimethyl sulphoxide—methanol—water and water as solvents, were found to have the lowest degree of resemblance. The increase in separation selectivity which can be generated by methanol dimethyl sulphoxide, is demonstrated for benzenecarboxylic acids.

Reactions in strongly basic media. Part 9. Correlation of the rates of methoxide-catalysed methanolysis of 1-substituted 2,4-dinitrobenzenes and 2-substituted 5-nitropyridines in methanolic dimethyl sulphoxide with an acidity function. Details of the mechanistic pathway

The rate coefficients for the methoxide-catalysed methanolysis of a series of 1-substituted 2,4-dinitrobenzenes and 2-substituted 5-nitropyridines have been measured in methanolic DMSO at 20.0 or 21.0 °C. For the 2-substituted 5-nitropyridines and for the 1-substituted 2,4-dinitrobenzenes below ca. 55 mol% DMSO, the rates have been correlated with an acidity function of the medium. The slopes of these linear relations are discussed. The 1-substituted 2,4-dinitrobenzenes above ca. 55 mol% DMSO give rise to Meisenheimer complexes as intermediates and/or as the product of the reaction. The product of the reaction then becomes the 1,1-Meisenheimer complex of methoxide and 2,4-dinitroanisole. For the 1-fluoro substrate the formation of the latter becomes rate determining. For other 1-substituted substrates the decomposition of a 1,3-Meisenheimer complex becomes rate determining.

Isotachophoresis in mixed solvents, consisting of water, methanol and dimethyl sulphoxide : II. Solvation effects on the acid—base and transport properties of cation acids of the ammonium ion type

The isotachophoretic behaviour of seventeen ammonium ions was investigated in water, methanol—water and dimethyl sulphoxide—methanol—water as solvents. The apparent p K values of the solutes were estimated and the changes with solvent composition are discussed, on the basis of the transfer activity coefficient. The pH of the electrolyte systems for isotachophoresis was chosen such that all the analytes were totally protonated. A direct measurement of the mobilities of the leading and reference ions was carried out by a moving boundary technique with an instrument normally used for isotachophoresis. With the aid of these values, the actual mobilities of the analytes were derived from their relative step heights. The changes in the ionic mobilities of the analytes with solvent composition are attributed to cation solvation effects. The ammonium ions were classified, according to their mobilities and the changes in the mobilities, respectively, in the different solvents. The physico-chemical significance of the resulting resemblances are discussed.

Reactions of carbonyl compounds in basic solutions. Part 9. Methoxide-catalysed cyclization of benzylidenephthalides and methyl o-phenylacetylbenzoates

The detailed mechanism of the methoxide-catalysed rearrangement of substituted benzylidenephthalides and both normal and pseudo methyl o-phenylacetylbenzoates to form 2-phenylindane-1,3-diones has been studied. A rate–acidity function correlation for the reactions in methanolic dimethyl sulphoxide (DMSO) shows a linear increase in rate with increasing H_ to reach a maximum in rate before decreasing, except for the p-nitro substrate. This derivative shows a rate decrease throughout the H_ range. The ρ values in methanol and in 94 mol% methanolic DMSO are 1.7 and –1.6, respectively. The kinetic isotope effect has been observed with kH/kD 0.8–1.0. The equilibrium constants for ring–chain tautomerism of the methyl o-phenylacetylbenzoates have been determined and shown to be independent of substituent and solvent composition. The rate-determining step is the intramolecular attack of the anion of the normal ester on the ester carbonyl group. In methanol and methanolic DMSO of high methanol content this is preceded by the ionization equilibrium of the normal ester. In methanolic DMSO of low methanol content and for the p-nitro substrate, the initial state is the anion itself.

Reactions of carbonyl compounds in basic solutions. Part 11. The Baker-Venkataraman rearrangement

The detailed mechanism of the Baker–Venkataraman rearrangement has been studied. The kinetics of the rearrangement of a series of 2-acetylphenyl 3- or 4-substituted benzoates and acetylnaphthyl benzoates catalysed by a basic ‘non-nucleophilic’ buffer in dimethyl sulphoxide have been measured. Studies of substituent effects, kinetic isotope effects, and acidity function correlations indicate a pathway involving pre-equilibrium formation of the carbanion, followed by rate-determining intramolecular nucleophilic attack. The methanolysis of the 2-acetylphenyl benzoates catalysed by methoxide in methanolic dimethyl sulphoxide has been similarly investigated. In this case the pathway appears to involve neighbouring group participation by the ketonic carbonyl group.

Reactions of carbonyl compounds in basic solutions. Part 10. Methoxide-catalysed cyclisation of methyl 2-acylbenzoates and 8-acyl-1-naphthoates

The detailed mechanism of the methoxide-catalysed rearrangement of both normal and pseudo methyl o-acylbenzoates and 8-acyl-1-naphthoates to form indane-1,3-diones and phenalene-1,3-diones, respectively, has been studied. Rate–acidity function correlations for the reactions in methanolic dimethyl sulphoxide give linear relations. The kinetic isotope effects have been observed with kH/kD equal to 0.7–0.9 and 5–7 for methyl o-acetylbenzoate and normal methyl 8-acetyl-1-naphthoate, respectively. The effect of substituents and ring–chain tautomerism on the rates has been considered. For the o-acylbenzoates the initial state is the ring-chain tautomeric equilibrium mixture and the rate-determining step is the intramolecular attack of the anion of the normal ester. For normal 8-acyl-1-naphthoates the rate-determining step is the ionisation of the normal esters; for the corresponding pseudo esters, the rate-determining step is the isomerisation of the psuedo to the normal ester.

Proton abstraction from bis-(2,4-dinitrophenyl)methane by methoxide ion

Rate constfnts for hydrogen or deuterium abstraction from bis-(2,4-dinitrophenyl)methane by methoxide ion have been determined in methanol, methanol–dimethyl sulphoxide, and deuteriated methanol solutions, together with the temperature variation of proton abstraction and carbanion protonation for the hydrogen-containing substrate in methanol. Isotope and solvent effects confirm the rate-limiting proton transfer.

Solvent dependence of the ionization of nitrophenylmethanes

The solvent dependence of proton abstraction from various nitrophenylmethanes has been examined for aqueous dimethyl sulphoxide and methanolic dimethyl sulphoxide solutions. Even though the compounds studied vary considerably in thermodynamic acidity (pKa), their proton-abstraction rates all show the same solvent dependence. It is suggested that the transition states for these reactions all occur at similar positions on the reaction pathway, and that transition state imbalances exist for these proton transfers.

Heterocyclic imines and amines. Part 18. Conversion of o-cyanobenzyl cyanide into isoquinoline, benzylisoquinoline, and azachrysene products

With sodamide in formamide, o-cyanobenzyl cyanide dimerises in the two ways possible: it also adds formamide to yield 1-amino-3-formamidoisoquinoline (2). Each dimer undergoes cycloisomerisation: thus 1-amino-3-o-cyanobenzyl-4-cyanoisoquinoline (5a) and 6,11-diamino-12-cyanobenzo[c]phenanthridine (9) were isolated. o-Cyanobenzyl cyanide with sodium methoxide afforded (5a) very slowly in methanol but much more rapidly in dimethyl sulphoxide–methanol.

Kinetics of reaction of 1-chloro-2,4,6-trinitrobenzene with enolate ions of 2,4-pentanedione and methyl 3-oxobutanoate

Reaction of 1-chloro-2,4,6-trinitrobenzene (I) with anions of 2,4-pentanedione (II) and methyl 3-oxobutanoate (III) produces 3-(2,4,6-trinitrophenyl)-2,4-pentanedione (IV) and methyl 2-(2,4,6-trinitrophenyl)-3-oxobutanoate (V), respectively, besides 2,4,6-trinitrophenol (VI). Amount of 2,4,6-trinitrophenol decreases with increasing amount of dimethyl sulphoxide and 2,4-pentanedione in methanol. A mechanism of formation of 2,4,6-trinitrophenol is suggested. Rate constant of formation of 3-(2,4,6-trinitrophenyl)-2,4-pentanedione in methanol-dimethyl sulphoxide mixtures increases with increasing content of dimethyl sulphoxide and decreases with increasing LiCl concentration. In methanol, 1-chloro-2,4,6-trinitrobenzene reacts with anion of 2,4-pentanedione about 20x slower than with anion of methyl 3-oxobutanoate.

Nucleophilic displacement in polyhalogenoaromatic compounds. Part 11. Kinetics of protiodeiodination of iodoarenes in dimethyl sulphoxide–methanol

The rates of methoxide-ion induced protiodeiodination of a number of polychloroiodobenzenes and their derivatives have been measured in dimethyl sulphoxide–methanol (9 : 1 v/v; 323.2 K). The true reagent under these conditions appears to be the dimethyl sulphoxide anion, and the rates of reaction in some cases appear to approach that expected of a diffusion controlled process. This corresponds to a major decrease in the efficacy of further activating substituents in the aromatic system, although deactivating groups such as p-OMe still show large effects. Chlorine promotes protiodeiodination in the order of efficiency o-Cl > m-Cl > p-Cl; the trifluoromethyl group activates displacement in the order o-CF3 > p-CF3 > m-CF3, although with much less difference between isomeric sites. o-Nitro-groups promote protiodeiodination whereas the p-nitro-group encourages methoxydeiodination. No evidence of methoxydeiodination was found in attack of the polychloroiodobenzenes, although the rates of methoxydechlorination of the corresponding polychlorobenzenes suggest that in some cases this might occur. Evidence rejecting the possible SRN1 mechanism and supporting nucleophilic attack by a carbanionic species upon iodine is presented.

Dicopper(II) complexes of a macrocyclic ligand containing single hydroxo-, methoxo-, or 1,1-azido-bridges: synthesis, magnetic properties, electron spin resonance spectra, and the crystal and molecular structure of a µ-hydroxo-derivative

Reaction of 2,6-diacetylpyridine with 1,3-diaminopropane in methanol in the presence of M[ClO4]2(M = SrII or BaII) in 2:1:1 molar proportions yields the complexes [ML2(ClO4)2] of the new 20-membered macrocyclic tetraimine ligand L2 derived from the [2 + 2] condensation of 2 mol of diketone with 2 mol of diamine. The single Ba2+ in [BaL2(ClO4)2] may be replaced by two Cu2+ to afford, depending on the conditions, the complexes Cu2L2(OH)(ClO4)3·2H2O and Cu2L2(OMe)(ClO4)3˙2H2O formulated as containing two Cu2+ linked by, respectively, single hydroxo- and methoxo-bridges. Crystals of the µ-hydroxo-complex are tetragonal with a= 15.20(1), c= 14.50(1)A, Z= 4, and space group P42/n. 1 191 Reflections above background were measured by diffractometer and refined by Fourier methods to R 0.078. Each copper atom in the binuclear [Cu2L2(OH)(OH2)]3+ cation is bonded to the three nitrogen atoms of a trimethine group of the folded macrocycle [Cu–N 1.916(13)–2.066(12)A]. The approximate co-ordination square plane about each metal atom is completed by a shared oxygen atom, O(1)(presumed to be from OH–), at 1.916(9)A. The two Cu atoms are also linked in a shared axial position by a second oxygen atom, O(2)(presumed to be from H2O), at 2.519(12)A. The Cu–O(1)–Cu and Cu–O(2)–Cu angles are 110.3(7) and 77.3(4)°, respectively, and the Cu ⋯ Cu separation is 3.145(4)A. Magnetic susceptibility measurements in the temperature range 90–300 K establish that the two Cu2+ in each binuclear complex are antiferromagnetically coupled with J=–32 and –53 cm–1 for the µ-hydroxy- and µ-methoxo-derivatives, respectively, where 2J is the singlet–triplet separation. The appearance of a ‘ triplet ’ e.s.r. spectrum at g≈ 2 and a seven-line ΔM= 2 half-band spectrum at g≈ 4 for frozen methanol–dimethyl sulphoxide solutions of the µ-methoxo-complex indicate retention of the bridge in solution. Reaction of Cu2L2(OMe)(ClO4)3·2H2O with Na[N3] affords Cu2L2(N3)(ClO4)3 for which i.r. spectra suggest that the Cu2+ are intramolecularly linked by one nitrogen atom of the azide ion (µ-1,1-N3 bridging mode). E.s.r. spectra of frozen solutions of the monoazide show that the Cu2+ are weakly antiferromagnetically coupled. The structures and physical properties of the complexes are discussed in relation to the cavity size of the macrocycle L2.

Selective solvation of Ag(I) iodate in methanol-dimethyl sulphoxide mixtures

The selective solvation of silver(I) iodate was studied in methanoldimethyl sulohoxide mixtures at 30° C by solubility and EMF measurements. The solubility of the salt increases continuously with the addition of dimethyl sulphoxide after a slight decrease into XDMSO =0.1. The Gibbs energy of transfer of silver cation (determined on the basis of ferrocene reference method) decreases continuously while that of the iodate ion increases with the addition of dimethyl sulphoxide. The solvent transport number passes through a maximum (Δ = 2.0) around XDMSO= 0.5. These results were interpreted as arising due to a heteroselective solvation of the salt, the silver ions being preferentially solvated by dimethyl sulphoxide and the iodate ion by methanol in these mixtures.

The stabilities of Meisenheimer complexes. Part 22. The ionisation of 2,4-dinitroaniline, its N-alkylated derivatives, and 2,6-dinitroaniline in methanol–dimethyl sulphoxide containing sodium methoxide

2,4-Dinitroaniline and its N-alkylated derivatives react with sodium methoxide in methanol–dimethyl sulphoxide to give the conjugate base. However, in the case of 2,6-dinitroaniline, base addition at the 3-position competes with proton loss. The effects of N-alkylation on the acidity of 2,4-dinitroaniline are considered and are compared with the effects of similar substitution in 2,4,6-trinitroaniline.

Kinetics and stereochemistry of elimination reactions in tertiary nitroalkanes: a measure of the nucleofugacity of nitrite ion from a saturated carbon

The reaction of methoxide ion in 50%, (v/v) methanol–dimethyl sulphoxide with p-(2-methyl-2-nitro-propyl)nitrobenzene and its derivatives shows that the elimination reaction taking place is a concerted anti-periplanar E2 process and that the nucleofugacity of nitrite ion in this system lies between that of bromide and chloride ions.