Acetonitrile-water Mixed Solvent Research Articles

Effect of Substituents on TiO2 Photocatalytic Oxidation of trans-Stilbenes

Abstract Photocatalytic reaction of trans-stilbene on TiO2 particles produces benzaldehyde with high selectivity in acetonitrile-water mixed solvent. Introduction of electron-donating substituents to the benzene rings accelerated the reaction. On the other hand, the rate was decelerated by electron-withdrawing substituents. These results suggest that the reaction proceeds by hydroperoxo or hydroperoxy, which were formed on TiO2 surface by UV irradiation, rather than free OH radicals.

One unexpected mixed-valence Cu(I,II)-cyanide coordination polymer in situ originating from the cleavage of acetonitrile

Solvothermal reaction of CuCl2·2H2O and 2-(4-pyridyl)benzimidazole (PyHBIm) in a acetonitrile-water mixed solvent afforded a mixture of [CuI2CuII(CN)2(PyHBIm)2Cl2]n (1) and [CuII(PyH2BIm)2Cl4] (2). Complex 1 is a mixed-valence 1D ribbon Cu(I,II)-cyanide coordination polymer. One Cu(II) center linearly links two Cu(I) ions via two μ2-CN bridges. XPS spectrum and bond valence sum (BVS) analysis have confirmed the mixed-valence characteristics. Cu(II) ion adopts a centrosymmetric square-planar geometry surrounded by two cyanides and two pyridyl groups. Cu(I) ions adopt a trigonal geometry coordinated by cyanide, imidazole group and Cl− anion. The cyanide ligand is in situ generated from the cleavage of acetonitrile solvent, which indicates that acetonitrile is an environmentally friend cyanating agent. The mechanism of acetonitrile in situ cleavage under solvothermal condition is explained. Complex 2 is a centrosymmetric mononuclear Cu(II) compound. Four equivalent Cl− anions lie on the equatorial plane. The protonated PyH2BIm+ cation as a monodentate ligand coordinates to Cu(II) center via pyridyl terminal.

Colorimetric Determination of Pyrophosphate Anion and Its Application to Adenylation Enzyme Assay

A colorimetric pyrophosphate assay based on the formation and reduction of the 18-molybdopyrophosphate ([(P2O7)Mo18O54](4-)) anion in an acetonitrile-water mixed solvent was modified and improved. The [(P2O7)Mo18O54](4-) anion is precipitated from the acetonitrile-water solution containing MoO4(2-) and HCl, and is re-dissolved in neat acetonitrile or propylene carbonate. This separation process decreases the interference by ATP, and prevents a yellow coloration of the reducing agent, ascorbic acid, due to excess Mo(VI) species. In the organic solvent, the [(P2O7)Mo18O54](4-) anion is reduced to a more intense blue molybdopyrophosphate species. The application of the colorimetry to the assay of adenylation enzymes is also described in this note.

Solvent Effects on the Kinetics of Amide Bond Cleavage in p-Chloro and p-Bromo Oxazolinones in Acetonitrile–Water Mixtures

The kinetics of amide bond cleavage in p-chloro and p-bromo oxazolinone have been studied using triethylamine as a base catalyst under pseudo-first order conditions, in the temperature range (303.15–333.15 K). The reaction rate was measured spectrophotometrically over a range of acetonitrile–water mixed solvent (30–70 %, v/v) compositions. The reaction rate was found to be faster for p-Cl than for p-Br oxazolinone. The thermodynamic parameters of activation were calculated: ∆G* increased gradually as the mole fraction of the cosolvent increased due to quasi-mirror image compensation of ∆H* and ∆S* (entropy–enthalpy compensation). The isokinetic temperature indicates that the reaction is enthalpy controlled. The reactivity was analyzed in the light of various simple and multiple regression equations using the Kamlet–Taft solvatochromic parameters.

Electrical conductivity of sodium polystyrenesulfonate in acetonitrile–water-mixed solvent media: experiment and data analysis using the Manning counterion condensation model and the scaling theory approach

Precise measurements on the electrical conductivity of sodium polystyrenesulfonate in acetonitrile–water-mixed solvent media containing 20 and 40 vol.% of acetonitrile at 308.15, 313.15, and 318.15 K are reported. The mobility of the polyelectrolyte solute was found to be influenced by the polyelectrolyte concentration, the relative permittivity of the medium, and the temperature. The Manning counterion condensation theory for salt-free polyelectrolyte solution failed to describe the experimental results. The data have, therefore, been analyzed on the basis of a new model for semidilute polyelectrolyte conductivity which takes into account the scaling arguments to obtain the fractions of uncondensed counterions which were found to depend on the polyelectrolyte concentration. The effects of the temperature and the relative permittivity of the medium on the equivalent conductivity as well as on the fraction of uncondensed counterions have also been discussed.

Intrinsic viscosities of sodium carboxymethylcellose in acetonitrile–water mixed solvent media using isoionic dilution method

AbstractPrecise measurements on the viscosities of the solutions of sodium carboxymethylcellulose in water and in two acetonitrile–water mixtures containing 10 and 20 vol % of acetonitrile have been reported at 35, 40 and 50 °C. Isoionic dilutions were performed with the total ionic strengths of the solutions maintained with sodium chloride at ∼4.20 × 10−4 and 1.45 × 10−3 mol dm−3 of NaCl to obtain the intrinsic viscosities. The Huggins constants were also obtained from the experimental results. The influences of the medium, the temperature, and the total ionic strength on the intrinsic viscosities as well as on the Huggins constants have been interpreted from the points of view of the solvodynamic and thermodynamic interactions prevailing in the polyelectrolyte solution under investigation. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1765–1770, 2007

Kinetics of the complexation of nickel(II) with 1,10-phenanthroline and its derivatives in acetonitrile–water mixed solvents

The kinetics of the complexation of Ni(II) with 1,10-phenanthroline(phen), 4,7-dimethyl-1,10-phenanthroline(dmphen), and 5-nitro-1,10-phenanthroline(NO 2phen) in acetonitrile–water mixed solvents of acetonitrile mole fraction x AN = 0, 0.05, 0.1, 0.2 and 0.3 at 288, 293, 298 and 303 K have been studied by stopped-flow method at ionic strength of 1.0 (NaClO 4) and pH 7.4. The corresponding activation enthalpy, entropy, and free energy were determined from the observed rate constants. The complexation of Ni(II) with the three ligands has comparable observed rate constants; in pure water the observed rate constants are (×10 3 dm 3 mol −1 s −1) 2.31, 2.57, and 1.38 for phen, dmphen and NO 2phen, respectively. The corresponding activation parameters for the three ligands are, however, considerably different; in pure water the Δ H ‡/Δ S ‡ (kJ mol −1/J K −1 mol −1) are 44.7/−30.2, 19.5/−114.1, and 32.2/−76.9 for phen, dmphen, and NO 2phen, respectively. The effects of solvent composition on the kinetics are also markedly different for the three ligands. The Δ H ‡ and Δ S ‡ showed a minimum at x AN = 0.1 for phen; for dmphen and NO 2phen, however, maxima at x AN = 0.2 were observed. Nevertheless, there is an effective enthalpy–entropy compensation for the Δ H ‡/Δ S ‡ of all the three ligands, demonstrating the significant effects of the changes in solvation and solvent structure on the complexation kinetics. As the rate-determining step of Ni(II) complexation is the dissociation of a water molecule from Ni(II), the solvent and ligand dependencies in the Ni(II) complexation kinetics are ascribed to the change in solvation status of the ligands and the altered solvent structures upon changing solvent composition.

Effects of Solvent Composition and Temperature on K+–18-Crown-6 Complexation in Acetonitrile–Water Mixed Solvents

Complexation of K+ by 18-crown-6 ether (18C6) in pure water and in acetonitrile–water mixed solvents containing 0.1 mol-dm− 3 (C2H5)4NCl has been systematically studied by isothermal titration calorimetry (ITC) at 293, 298, and 303 K. The formation constant K of the 1:1 [K(18C6)]+ complex and the complexation enthalpy Δ rH were simultaneously determined from the titration data. The logK and Δ rH(kJ-mol− 1) values at 298 K are 2.04, −26.2 in pure water and 2.23, −25.0; 2.61, −24.2; 2.95, −23.8; 3.48, −21.0; 3.85, −19.4; 4.36, −18.7; and 5.73, −17.0 in the mixed solvents at xAN (mole fraction of acetonitrile) of 0.043, 0.135, 0.258, 0.448, 0.578, 0.759, and 1.0, respectively. The change in heat capacity for the complex formation, Δ C p °, was also determined by the temperature dependence of Δ rH. Whereas the Δ C p ° is (57 ± 11) and (63 ± 20) J-mol− 1-K− 1 in pure water and in the solvent mixture at xAN = 0.043, respectively, it decreases with increasing xAN. The Δ C p ° values are −(48 ± 11), −(110 ± 25), −(354 ± 40), −(359 ± 24), and −(304 ± 30) J-mol− 1-K− 1 at xAN = 0.135, 0.258, 0.448, 0.578, and 0.759, respectively. The changes in complexation thermodynamics (Δ Δ rG, Δ ΔrH, and Δ Δ rS) are discussed in terms of the corresponding transfer thermodynamics of K+, 18-crown-6, and [K(18C6)]+ upon transferring from water to acetonitrile–water mixed solvents. It was found that hydrophobic solvation of the complex [K(18C6)]+ plays an important role in complex formation occurring in water and in the water-rich mixed solvent. Moreover, changes in solvent structure significantly affect the transfer enthalpy and entropy of each species, i.e., K+, 18-crown-6, and [K(18C6)]+. The observed monotonous changes in the complexation Gibbs energy, enthalpy, and entropy with solvent composition are due to the effective compensation of the Δ trG, Δ trH, and Δ trS for K+ with those for 18-crown-6 and [K(18C6)]+.

Oxidation of dibenzothiophene by hydrogen peroxide or monopersulfate and metal–sulfophthalocyanine catalysts: an easy access to biphenylsultone or 2-(2′-hydroxybiphenyl)sulfonate under mild conditions

A catalytic system consisting of metal–sulfophthalocyanines (MPcS) and monopersulfate or hydrogen peroxide as oxidants was effective in the dibenzothiophene oxidative desulfurization with various yields and selectivities. Oxidations were conducted at room temperature in acetonitrile–water mixed solvent. The dibenzothiophene oxidation involved the step by step formation of dibenzothiophene dioxide and biphenylsultone (dibenzo-1,2-oxathiine 2,2-dioxide), followed by hydrolysis to 2(2′-hydroxybiphenyl)sulfonate and finally catalytic desulfurization to 2-hydroxybiphenyl (2-phenylphenol) and sulfuric acid; all the intermediate compounds were identified. Moreover, catalytic over-oxidation of 2-hydroxybiphenyl, with ring fission and formation of various oxidation products, among them carbon dioxide, oxalic and benzoic acid, was also observed. Among the various MPcS catalysts examined (M = Fe, Co and Ru), the ruthenium derivative exhibited the best performances with persulfate and iron derivative with hydrogen peroxide; in both cases the slow step of the process consisted in the oxidation of dibenzothiophene dioxide to biphenylsultone.

Small-angle X-ray scattering from semi-dilute solutions of poly(N-isopropylacrylamide) in aqueous acetonitrile solutions

Interaction parameters of poly(N-isopropylacrylamide) in acetonitrile–water mixed solvent were determined by using small-angle X-ray scattering. Small-angle X-ray scattering measurements were carried out in conditions of the semi-dilute poor solvent regime and just below the lower critical solution temperature. From concentration dependence of the correlation length, the binary and ternary cluster integrals were determined. The contribution of the segment–segment interactions to the entropy S int and the enthalpy H int has been calculated from the temperature dependence of these cluster integrals. It has been found that both values are positive. On addition of a small amount of acetonitrile into aqueous solution of poly(N-isopropylacrylamide), S int and H int increase with increasing acetonitrile content. Upon further addition of acetonitrile, these values decreased.

On the role of solvent in acid–base equilibria of diuretics in acetonitrile–water mixed solvents

The dissociation constants of representative loop (furosemide), thiazide (chlorthiazide and trichlormethiazide) and potassium sparing (amiloride) diuretics in 10, 30, 40, 50 and 70% (w/w) acetonitrile–water mixtures at 298.15 K were determined, in accordance with IUPAC procedures. The variation in p K a values over the whole composition range can be explained by preferential solvation and the structural features in acetonitrile–water mixtures. Correlations between p K a values and various bulk and solvatochromic properties of the solvents were calculated. The linear solvation energy relationship (LSER) method was applied. The resulting equations allowed us to calculate p K a values for the diuretics studied in any acetonitrile–water mixture up to 70% (w/w) and should help to clarify the acid–base behaviour of diuretics in the widely-used acetonitrile–water mixed solvents.

Cycloauration of 2-substituted pyridine derivatives. Synthesis, structure and reactivity of six-membered cycloaurated complexes of 2-anilino-, 2-phenoxy- and 2-(phenylsulfanyl)-pyridine

At room temperature and in ethanol 2-anilinopyridine reacted with H[AuCl4]·4H2O as well as Na[AuCl4]·2H2O to give directly the six-membered cycloaurated complex [AuCl2(pap-C 1, N)] 1a [pap = 2-(2-pyridylamino)phenyl], whereas 2-phenoxypyridine (Hpop) and 2-(phenylsulfanyl)pyridine (Hptp) produced only the salts [H2pop][AuCl4] 2b and [H2ptp][AuCl4] 2c, respectively. The adducts [AuCl3(Hpop)] 3b and [AuCl3(Hptp)] 3c have separately been prepared by the reactions of Na[AuCl4]·2H2O with Hpop and Hptp, respectively, in an acetonitrile–water mixed solvent. The salts 2b and 2c can be converted into the corresponding adducts 3b and 3c when they are stirred in acetonitrile–water at room temperature. The cycloaurated complexes [AuCl2(pop-C 1, N)] [pop = 2-(2-pyridyloxy)phenyl] 1b and [AuCl2(ptp-C 1, N)] [ptp = 2-(2-pyridylsulfanyl)phenyl] 1c have been obtained by heating the salts or the adducts in acetonitrile–water. Moreover, complexes 1b and 1c have been synthesized directly by the reaction of H[AuCl4]·4H2O with Hpop and Hptp in refluxing acetonitrile–water, ethanol–water and propan-2-ol–water. The reaction of 1a with an equimolar amount of PPh3 in the presence of NaBF4 gave the cationic complex [AuCl(pap-C 1, N)(PPh3)]BF4 5a, while two equivalents of PPh3 or PEt3 afforded [AuCl(pap-C1)(PPh3)2]Cl 6a or [AuCl(pap-C1)(PEt3)2]Cl 7a where the pap ligand co-ordinates through only the carbon atom. On the other hand, the C–N chelates in 1b and 1c are easily cleaved with one equimolar amount of PPh3 to give [AuCl2(pop-C1)(PPh3)] 8b and [AuCl2(ptp-C1)(PPh3)] 8c, respectively. The boat-form structures of the three six-membered auracycles have been confirmed by X-ray diffraction studies of 1b, 1c and 5a. The crystal structure of 7a has also been determined.

Evaluation of the effect of organic modifier on p K values of diuretics in mobile phases used in LC

The dissociation p K values of a series of diuretics in 10, 30, 40, 50 and 70% (w/w) acetonitrile–water mixed solvents at 25°C were determined according to the criteria endorsed by IUPAC. The series of diuretics chosen includes compounds with differences in molecular structures and physico-chemical properties. Acidic compounds (loop diuretics, such as furosemide, bumetanide and ethacrynic acid), weakly acidic (thiazides, such as chlorthiazide and trichlormethiazide), neutral (aldosterone antagonists, such as canrenone) and basic compounds (potassium-sparing diuretics, such as amiloride and triamterene) were all considered. The variation of the p K values obtained over the whole composition range studied can be explained by taking into account the preferential solvation of ionizable compounds in acetonitrile–water mixtures. Moreover, in order to obtain p K values in any of the unlimited number of possible binary solvent acetonitrile–water mixtures, relationships between p K values and different bulk properties were examined, and the linear solvation energy relationships method (LSER) was applied to study the correlations of p K values with the solvatochromic parameters π*, α and β of acetonitrile–water mixtures. The equations obtained allowed calculation of the p K values of diuretics in any acetonitrile–water mixtures up to 70% (w/w) and thus permitted the acid–base behaviour of these important substances in the widely used acetonitrile–water media to be known.

Solvent effects on protonation equilibria of peptides and quinolones by factor analysis applied to the correlation between dissociation constants and solvatochromic parameters in acetonitrile-water mixtures

Dissociation constant values of series of peptides and quinolones in 5.54, 10, 16.3, 25 and 50% (w/w) acetonitrile-water mixed solvents at 298.15 K were, firstly, submitted to factor analysis in order to obtain the number of factors which affects the variation of the whole data sets and, afterwards, to target factor analysis to identify these factors. The p K values were correlated with the Kamlet and Taft solvatochromic parameters (α, β and π ∗) of acetonitrile-water mixtures according to the results obtained through these chemometric techniques. The equation proposed allowed the calculation of p K values of peptides in any acetonitrile-water mixture up to 50% (w/w) and, therefore, the acid-base behaviour of these compounds in widely used acetonitrile-water media is to be known. Further, an overview of the effect of preferential solvation of electrolytes in acetonitrile-water mixtures on the values of the protonation constants in these media was also obtained.

Acid-base behaviour of tripeptides in solvents used in liquid chromatography. Correlation between p K values and solvatochromic parameters of acetonitrile-water mixtures

The dissociation constant values of a series of tripeptides in 5.54, 10, 16.30, 25.03 and 50% (w/w) acetonitrile-water mixed solvents at 298.15 K were determined, according to the criteria endorsed by IUPAC. A pronounced change in the acid-base p K values of carboxylic and phenolic groups was observed as the solvent was enriched in acetonitrile. Dissociation constant values of protonated terminal amino groups are slightly influenced by the addition of acetonitrile. The variation of p K values was explained by taking into account the preferential solvation of electrolytes in acetonitrile-water mixtures and electrostatic effects. Correlations of p K values and different bulk and microscopic properties of the solvents were examined and the Linear Solvation Energy Relationships (LSER) methodology was applied. The equation obtained permits calculation of p K values of the tripeptides in any acetonitrile-water mixture up to 50% (w/w) and can help to clarify the acid-base behaviour of tripeptides in the widely used acetonitrile-water mixed solvents.

Variation of acidity constants of peptides in acetonitrile-water mixtures with solvent composition: effect of preferential solvation.

The dissociation constant values of a series of peptides in 5.54, 10, 16.30, 25.03 and 50% (w/w) acetonitrile-water mixed solvents at 298.15 K were determined according to the criteria endorsed by IUPAC. A pronounced change in the acid-base pK values of carboxylic, phenol and thiol groups was observed as the solvent was enriched in acetonitrile. By contrast, pK values of protonated amino-terminal groups were influenced slightly as the solvent was enriched in acetonitrile, although continually increasing pK values were observed. The variation of the pK values obtained, over the whole composition ranged studies, was explained by taking into account the preferential solvation of electrolytes in acetonitrile-water mixtures. To obtain pK values in all possible binary solvent acetonitrile-water mixtures, relationships between pK values and different bulk properties were examined and the Linear Solvation Energy Relationships methodology was applied. The pKa values were then correlated with the Kamlet-Taft, phi, alpha and beta solvatochromic parameters of acetonitrile-water mixtures. The equations obtained allowed calculation of the pK values of peptides in acetonitrile-water mixtures up to 50% (w/w) and thus permitted the acid-base behavior of these substances in the widely used acetonitrile-water media to be known.

Assignment of reference pH-values to primary standard buffer solutions for standardization of potentiometric sensors in acetonitrile-water mixtures.

Standard pH-values pH(PS) for seven primary standard buffer solutions in 0, 10, 30, 40, 50, 70 and 100% (w/w) acetonitrile-water mixed solvents at 298.15 K were determined according to the criteria recently endorsed by IUPAC. The preferential solvation of the ions in acetonitrile-water mixtures was studied in order to clarify the acid-base behaviour of the solutes in such mixtures. The influence of variation in the solvent composition on pH(PS) values was considered with a view to obtaining correlations that can be used to determine the pH(PS) values in any acetonitrile-water mixture up to 70% (w/w) acetonitrile. The pH(PS) values were then correlated with the weight and volume percentages and molar fraction of acetonitrile and with the Kamlet-Taft, pi(*), alpha and beta solvatochromic parameters of the acetonitrile-water mixtures. The equations obtained permit the standardization of potentiometric sensors in these mixtures.

Standard pH values for potassium hydrogenphthalate reference buffer solutions in acetonitrile—water mixtures up to 70 wt% at various temperatures

Reference value standards, pHs, for 0.05 mol kg −1 potassium hydrogenphthalate (KHPh) reference buffer solutions in 30, 50 and 70 wt% acetonitrile—water mixed solvents at temperatures from 288.15 to 308.15 K have been determined from emf measurements of the reversible cell Pt|Ag|AgCl|KHPh + KCl|Quinhydrone|Pt, in which the H +-reversible quinhydrone electrode replaces the ill-behaving hydrogen electrode. Values of the first ionization constant of the o-phthalic acid (H 2Ph; benzene-1,2 dicarboxylic acid) in these mixed solvents have also been determined from analogous measurements. The consistency of the present results with the previously determined pHs values in 5, 15 and 30 wt% acetonitrile—water mixtures is analysed by multilinear regression of pHs as a function of both solution composition and temperature. These smoothed standard pHs values are used to optimize the parameters of an equation predicting pHs values in different aqueous organic solvents.

Preferential Solvation of Single Ions: Standard Gibb's Free Energies of Transfer for the Ag+ Ion from Water to Acetonitrile-Water Mixed Solvents

Article Preferential Solvation of Single Ions: Standard Gibb's Free Energies of Transfer for the Ag+ Ion from Water to Acetonitrile-Water Mixed Solvents was published on January 1, 1980 in the journal Zeitschrift für Physikalische Chemie (volume 121, issue 1).

LIFETIME OF RHODAMINE B RADICAL CATION IN ACETONITRILE–WATER MIXED SOLVENTS

Abstract The rotating ring-disk electrode (RRDE) technique was used to measure the lifetime (τ) of rhodamine B radical cation (RhB\underset.+) in acetonitrile–water mixed solvents. The result can best be represented by τ=0.75[H2O]−1 (s), indicating that the principal pathway in the decay of RhB\underset.+ is through a bimolecular reaction with H2O.