Water-methanol Medium Research Articles

Aqueous Reduction of [Cp*2W2O5]: Characterization of the Triangular Clusters [Cp*3W3O4(OH)2]2+and [Cp*3W3O6]+– Comparison with Molybdenum

Zinc reduction of Cp*2W2O5 in an acidified water–methanol medium affords the green 3-electron trinuclear cluster [Cp*3W3O4(OH)2]2+, isolated and crystallographically characterized as the triflate salt, 1. Upon exposure to air, this complex is oxidized to a related 2-electron cluster, [Cp*3W3O6]+, which was crystallized and characterized in three different salts, 2–4. The 3-electron cluster exhibits a near-tetragonal frozen-glass EPR spectrum, and it shows evidence of coupling of the unpaired electron to only one of the three W atoms. The two-electron cluster is diamagnetic. An electrospray ionization MSn study revealed a stepwise expulsion of neutral [Cp*WO2] units as the main fragmentation process. DFT calculations unveiled the intimate details of the electronic structures of these complexes and fully rationalized the structural and spectroscopic properties.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Encapsulation efficiency and controlled release characteristics of crosslinked polyacrylamide particles

Polyacrylamide (pAAm) particles crosslinked with N, N-methylenebis-acrylamide/ethylene glycol dimethacrylate (NNMBA/EGDMA) have been prepared in water–methanol medium by the dispersion polymerization using poly(vinyl pyrrolidone), PVP as a steric stabilizer. 5-fluorouracil an anticancer drug, has been loaded in situ into the crosslinked pAAm particles. Plain as well as drug loaded microparticles have been characterized by differential scanning calorimetry (DSC) and X-ray diffraction studies (XRD) and scanning electron microscopy (SEM). DSC and XRD studies have indicated a molecular level dispersion of the drug in pAAm particles during in situ loading and SEM pictures have shown the formation of spherical and oval-shaped particles. In vitro release of 5-fluorouracil from the crosslinked pAAm particles has been carried out in 7.4 pH buffer medium. Both encapsulation efficiency and release patterns are found to depend on the nature of the crosslinking agent, amount of crosslinking agent used and the amount of drug loaded. In vitro release studies indicated the controlled release of 5-fluorouracil up to 12 h.

Analysis of complex formation between crown ethers and potassium ion by determining retention factors in reversed-phase high-performance liquid chromatography

Retention factors in reversed-phase high-performance liquid chromatography (RP-HPLC) were utilized for the analysis of complex formation reaction of four crown ethers with potassium ion in water–methanol media. The crown ethers were injected as analytes, potassium ion was present in the eluent, and three types of reversed-phase columns were used. The retention factor of the crown ethers decreased with increasing concentrations of potassium ion in the eluent, which is attributed to the change in the species of the crown ether from a neutral ligand to a positively charged complex. The complex formation constants were determined by analyzing the changes in the retention factor with a non-linear least-squares method.

Determination of the p Ka values of β-blockers by automated potentiometric titrations

The acid–base equilibrium constants of the β-blockers atenolol, oxprenolol, timolol and labetalol were determined by automated potentiometric titrations. The p K a values were obtained in water-rich or water–methanol medium (20% MeOH) to obviate the solubility problems associated with the compounds. The initial estimates of p K a values were obtained from Gran's method and then, were refined by the NYTIT and ZETA versions of the LETAGROP computer program. The resultant values were 9.4 ( I=0.1 M KCl, 20% methanol) for atenolol, 9.6 ( I=0.1 M KCl) for oxprenolol, 9.4 ( I=0.1 M KCl, 20% methanol) for timolol and 7.4 and 9.4 ( I=0.1 M KCl) for labetalol. The potentiometric method was found to be accurate and easily applicable. The operational criteria for applying the methodology are indicated.

A Rapid HPLC Determination of C 2 -C 7 Aliphatic Diamines by Precolumn Derivatization with Acetylacetone in Methanol-Water

A rapid reversed-phase high performance liquid chromatographic analysis for the determination of seven aliphatic diamines in water is described. Precolumn derivatization with acetylacetone is used for traces of aliphatic diamines in water-methanol (10:1 v/v) medium. The acetylacetone derivatives obtained after 15 min were extracted with an octadecylsilane functionalized silica cartridge, and then injected into the HPLC system. The HPLC system consisted of a reversed-phase column, and a spectrophotometric detector adjusted to 310 nm as elution solvent a methanol-tetrahydrofuran-water (55:3:42 v/v) mixture was used. The acetylacetone derivatives of the C2-C7 diamines were separated with a good resolution in 23 min. The detection limits achieved for each diamine were between 0.18–0.72 ng/ml for a 100 ml water sample. The recovery of diamine derivatives from river and seawater was 88–101%, with relative standard deviations of 2.2–4.0%, and 82–93%, with relative standard deviations of 2.8–4.6%, respectively.

Reduction of carbon monoxide by molybdenum-containing hydroxide systems

The reduction of CO by the nitrogen-fixing systems Ti(OH)3−Mo(OH)3 and MgTi2O4−Mo(OH)3 was studied in aqueous and water-methanol media; in the latter,14CO was used as the reagent. The main reaction product is methanol, whose yield in the H2O−MeOH−KOH mixture is almost an, order of magnitude higher than that in an aqueous alkaline solution. The data obtained were compared to those for the reduction of N2

Graft copolymerization of methacrylic acid onto isotactic polypropylene by radiochemical methods

Graft copolymerization of methacrylic acid onto isotactic polypropylene has been studied in water–methanol medium using γ-rays as the source of initiation. Graft copolymerization has been conducted by (1) mutual irradiation, (2) preirradiation, and (3) double irradiation methods. All of the reaction parameters that seem to influence grafting have been studied, and the optimum conditions leading to maximum percentage of grafting have been evaluated. A plausible mechanism for radiation-induced grafting of methacrylic acid onto polypropylene has been suggested, and the results have been explained on the basis of the proposed mechanism. A comparative study of graft copolymerization by different radiation methods has been made, and it was observed that the preirradiation method affords the best results. Evidence of grafting has been obtained from differential scanning calorimetric analysis and the dyeing behavior of the grafted material. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 143–152, 1998

Grafting onto wool. XXX. Effects of solvent composition on the radiation-induced graft copolymerization of some acrylates onto wool fiber

Radiation-induced graft copolymerization of ethyl methacrylate (EMA), ethyl acrylate (EA), methyl acrylate (MA), and methyl methacrylate (MMA) onto wool fiber by mutual method has been studied as a function of the composition of water-alcohol medium. Grafting of EMA, EA, and MA has been studied in nitrogen atmosphere, whereas grafting of MMA was carried out in air. Percentage of grafting (Pg) has been determined as a function of different reaction parameters that influence graft copolymerization. For all the monomers studied, it is observed that (1) maximum grafting is obtained at an optimum composition of water-alcohol medium; (2) Pg is considerably less in pure water or alcohol; (3) Pg of MA falls more sharply on addition of larger amount of MeOH to water-methanol medium as compared to EA and EMA; (4) in the case of grafting of MMA, water-isopropanol is a better reaction medium than the water-ethyl alcohol; and (5) Pg decreases considerably in air for all the monomers studied. A suitable explanation is suggested to account for these observed trends.

Grafting onto wool. XXX. Effects of solvent composition on the radiation‐induced graft copolymerization of some acrylates onto wool fiber

Radiation-induced graft copolymerization of ethyl methacrylate (EMA), ethyl acrylate (EA), methyl acrylate (MA), and methyl methacrylate (MMA) onto wool fiber by mutual method has been studied as a function of the composition of water-alcohol medium. Grafting of EMA, EA, and MA has been studied in nitrogen atmosphere, whereas grafting of MMA was carried out in air. Percentage of grafting (Pg) has been determined as a function of different reaction parameters that influence graft copolymerization. For all the monomers studied, it is observed that (1) maximum grafting is obtained at an optimum composition of water-alcohol medium; (2) Pg is considerably less in pure water or alcohol; (3) Pg of MA falls more sharply on addition of larger amount of MeOH to water-methanol medium as compared to EA and EMA; (4) in the case of grafting of MMA, water-isopropanol is a better reaction medium than the water-ethyl alcohol; and (5) Pg decreases considerably in air for all the monomers studied. A suitable explanation is suggested to account for these observed trends. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 191–195, 1997

Electropolymerization of 2-hydroxybenzothiazole (2-OHBT) in water–methanol media: electrochemical behaviour in NaCl (3%) solution

A new insulating thin polymer (<0.1μm) formed by the electropolymerization of 2-OHBT is reported. The anodic oxidation of 2-OHBT on copper, iron and platinum in alcohol and alcohol–water solutions are investigated using cyclic polarization and chronoamperometry. Scanning electronic microscopy (SEM) and energy dispersive X-ray spectrometry (EDX) are performed to confirm the presence of the organic layer. Based on the results obtained, a model for the formation mechanism is proposed. The corrosion behaviour of the coated copper is studied in NaCl (3%) solution by impedance spectrometry and anodic polarization. The results of these experiments show a decrease in the dissolution of copper due to the barrier properties of the organic coating.

Carbonylative reduction of aromatic nitroderivatives to arylamines catalyzed by sulfur compounds

Aromatic nitroderivatives e.g. nitrobenzene can be carbonylatively reduced with CO in water-methanol media, at 120–150°C and 10–15 MPa pressure. Aniline is obtained with selectivity over 97% at 100% nitrobenzene conversion. Reaction proceeds in the presence of multicomponent catalyst consisting of the base (favourable are the strong bases: sodium hydroxide or methoxide) and sulfur compound. The ratio of catalytic effectiveness of sulfur compounds is as follows S:CS 2:H 2S:COS = 1:1.3:10:10. Vanadium (V) compound can be added to improve selectivity of aniline formation. Aromatic dinitroderivatives undergo this reaction and selectivity to one of two main products (phenylenediamine or nitroaniline) can be switched by the choice of reaction conditions.

Kinetics and mechanisms of oxidation of thiosemicarbazide, its metal complex and hydrazones byN-chlorobenzamide in water methanol medium

The kinetics of oxidation of thiosemicarbazide (TSC) its zinc metal complex and hydrazones by N-chlorobenzamide (NCB) were investigated in water methanol (1 : 1, v/v) medium in the presence of perchloric acid. The hydrazones studied were benzaldehyde, propionaldehyde, acetone and acetophenone thiosemicarbazones. The reactions show first-order kinetics in [NCB], a fractional order dependence in [substrate] and an inverse fractional to inverse first order in [H+]. Addition of benzamide has no significant effect on the rates of oxidations. Variation in the ionic strength of the medium has little effect on the rates of reactions, but a decrease in the dielectric constant of the medium by increasing the methanol concentration in the solvent increases the rates. The rate-limiting steps were identified in all cases and the rate coefficients of these steps and the related activation parameters were also evaluated. The consistency of the deduced rate laws was checked by recalculating the rate constants as the substrate and H+ concentrations were varied.

The Polarographic Determination of 1-[4'-(Phenylazo)phenyl]-3,3-dimethyltriazene

A study has been made of the polarographic behaviour of genotoxic 1-[4'-(phenylazo)phenyl]-3,3-dimethyltriazene in mixed water-methanol medium. A mechanism has been proposed for its polarographic reduction and optimal conditions have been found for its determination by tast polarography in the concentration range 1 . 10-4 - 2 . 10-6 mol l-1 and using differential pulse polarography in the concentration range 1 . 10-4 - 2 . 10-7 mol l-1.

ChemInform Abstract: Kinetics and Mechanism of Oxidation of Thiocarbohydrazide by N‐ Chlorosuccinimide in Aqueous and Water‐Methanol Media

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Kinetics and Mechanism of Oxidation of Thiocarbohydrazide by N-Chlorosuccinimide in Aqueous and Water-Methanol Media

Article Kinetics and Mechanism of Oxidation of Thiocarbohydrazide by N-Chlorosuccinimide in Aqueous and Water-Methanol Media was published on February 1, 1990 in the journal Zeitschrift für Physikalische Chemie (volume 167, issue 2).

Kinetics and Mechanism of Oxidation of Thiocarbohydrazide by N-Bromoacetamide and N-Chlorobenzamide in Buffered Aqueous and Water-Methanol Media

Kinetics and Mechanism of Oxidation of Thiocarbohydrazide by N-Bromoacetamide and N-Chlorobenzamide in Buffered Aqueous and Water-Methanol Media

The polarographic and voltammetric determination of the 3'-halogen derivatives of N,N-dimethyl-4-aminoazobenzene

The polarographic reduction of the 3'-halogen derivatives of N,N-dimethyl-4-aminoazobenzene was studied in mixed water-methanol medium and optimum conditions were found for the determination of these genotoxic substances by tast polarography in the concentration range 1 . 10-4 to 2 . 10-6 mol l-1, differential pulse polarography at a dropping mercury electrode in the range 1 . 10-4 to 2 . 10-7 mol l-1 and fast scan differential pulse voltammetry at a hanging mercury drop electrode in the range 1 . 10-6 to 2 . 10-8 mol l-1. The increase in the sensitivity resulting from adsorptive accumulation of the studied substances on the surface of a hanging mercury drop can be utilized in the determination using the latter method in the concentration range 1 . 10-8 to 2 . 10-9 mol l-1.

Kinetics and Mechanism of Oxidation of Amino Acids by Dichloramine T

Abstract Kinetics of oxidations of several amino acids (alanine, leucine, aspargine, glutamine, and proline) by N,N-dichloro-p-toluenesulfonamide (generally known as dichloramine-T) have been studied in 1:1 (v/v) water–methanol medium in the presence of perchloric acid. The oxidations of alanine and leucine showed second order kinetics in [oxidant], first order in [amino acid] and inverse fractional order in [H+] over the entire range of [HClO4](0.0005–0.10 mol dm−3) used. But the kinetics of oxidations of aspargine, glutamine, and proline were [H+] dependent. The rate dependence in [oxidant] was second and first orders in [H+] ranges 0.0005–0.005 mol dm−3 and 0.005–0.10 mol dm−3, respectively. The kinetics in [amino acid] for these oxidations were also different. Variation in ionic strength of the medium or addition of the reduced product of the oxidant had no or negligible effects on the rates of reactions. Decrease in dielectric constant of the medium by increasing the methanol composition of the solvent decreased the rate in all the cases. Activation parameters have been computed from the Arrhenius plots. Plausible mechanisms consistent with the observed kinetics have been discussed.

Optimization of the Micro-Scale Determination of Arsenates by Direct Potentiometric Titration with Silver Ions and its Application to the Determination of Arsenic in-Organic Compounds

Abstract A micro-scale argentimetric method for the determination of orthoarsenates by potentiometric detection of the end-point has been developed. The optimal results were obtained when this titration was carried out in water-methanol medium, buffered at pH 7.50. This method minimizes the error of old methods arising from the small coprecipitation of silver oxide near the equivalence point and the data obtained are characterized by good accuracy and reproducibility. The procedure to perform the titration with an automatic apparatus is described as well as the optimum concentration range and titration rate. The method was then applied to the determination of arsenic in organic compounds after mineralization in the Schoniger flask using a quartz spiral.

Kinetics and mechanism of oxidation of thiocarbohydrazide in the free state and in its metal complex and thiocarbohydrazone by chloramine-T and dichloramine-T

Kinetics of oxidation of thiocarbohydrazide (TCH) in the free state and as its metal complex, and as a hydrazone by chloramine-T (CAT) in aqueous HClO4 medium, and by dichloramine-T (DCT) in 1:1 (v/v) water-methanol medium in the presence of HClO4 have been studied. Rates of oxidation of TCH in the free state and in metal complex by CAT were determined. The rate law for the oxidation of TCH at high [H+ ] and for complex oxidations were identical to that for CAT oxidations. The conversion of TCH into its hydrazone changed the order in [H+] from a positive to a negative value, probably signalling the change of reaction site. The rate law for oxidation under these conditions was determined. Addition of the reduced product of the oxidants had no effect on the rate of oxidations. Variation in ionic strength of the medium had little positive effect, while decrease in dielectric constant of the medium decreased the rate in both the oxidations. Oxidation processes generally follow a Michaelis-Menten type of mechanism. Constants of the rate limiting steps have been calculated at different temperatures and these constants have been used to calculate the activation parameters from the Arrhenius plots. The proposed mechanisms are supported by investigations with HOC1 under identical reaction conditions. Metal complexation of the substrate decreased the reactivity, while conversion of TCH into its hydrazone changed the rate dependence on [H+].