Supercritical thermal decompositions of normal- and iso-dodecane in tubular reactor

Thermal decompositions of a serials of normal- and iso-dodecane mixtures with different iso/normal ratios were performed in a tubular reactor under supercritical conditions (550-680 °C, 4.0 MPa). It was found that iso-dodecane has an accelerating effect on the pyrolysis of n-dodecane depending upon iso/normal ratio of the mixture, and that accelerating factor reaches up to almost 4 at iso/normal ratio of 3/1. Decomposition conversions of the mixtures show a strong dependence on the iso/normal ratio and the temperature owing to their possible effect on the radical generation mechanism and the decomposition kinetics. In addition, iso/normal ratio of the mixture also affects the formation rates and morphologies of cokes due to the variation of decomposition conversion.     

Computer-aided carbon-13 nuclear magnetic resonance spectroscopy for identification of terpenoid mixtures

The procedure for identifying triterpenes in mixtures is based on the simulation of ¹³C-NMR spectra for probable mixtures and comparison of these with a specialized spectral data bank. The system was designed to facilitate the analysis of complex mixtures of terpenoid compounds. A special matching procedure was developed and its efficiency is discussed. The method is demonstrated for a mixture of five triterpenes isolated from Vernonia cognata.     

Determination of triacylglycerol regioisomers using electrospray ionization-quadrupole ion trap mass spectrometry with a kinetic method

The kinetic method was applied to differentiate and quantify mixtures of regioisomeric triacylglycerols (TAGs) by generating and mass selecting alkali ion bound metal dimeric clusters with a TAG chosen as reference (ref) and examining their competitive dissociations in a quadrupole ion trap mass spectrometer. This methodology readily distinguished pairs of regioisomers (AAB/ABA) such as LLO/LOL, OOP/OPO and SSP/SPS and consequently distinguished sn-1/sn-3, sn-2 substituents on the glycerol backbone. The dimeric complex ions [ref, Li, TAG_{(AAB and/or ABA)}]⁺ generated by electrospray ionization mass spectrometry were subjected to collision induced dissociation causing competitive loss of either the neutral TAG reference (ref) leading to [Li(AAB and/or ABA)]⁺ or the neutral TAG molecule (TAG_{(AAB and/or ABA)}) leading to [ref, Li]⁺. The ratio of the two competitive dissociation rates, defined by the product ion branching ratio (R_iso), was related via the kinetic method to the regioisomeric composition of the investigated TAG mixture. In this work, a linear correlation was established between composition of the mixture of each TAG regioisomer and the logarithm of the branching ratio for competitive fragmentation. Depending on the availability of at least one TAG regioisomer as standard, the kinetic method and the standard additions method led to the quantitative analysis of natural TAG mixtures.     

Spectrophotometric determination of aromatic and heterocyclic amino acids in mixtures

A procedure for the determination of individual aromatic and heterocyclic amino acids in mixtures was developed with the use of the Vierordt method. Amino acids can be simultaneously determined by this procedure in the concentration range (0.4-3.0) x 10^-3 M. The determination errors for binary and ternary mixtures were no greater than 5 and 10%, respectively. The determination error increases with a decrease in the concentration of a particular component and with an increase in the number of components in the test mixture.     

Binary solid-liquid phase diagram of the two diastereomer racemates of triglycidyl isocyanurate (TGIC)

Triglycidyl isocyanurate [2451-62-9] as a trifunctional epoxy monomer is mostly used as curing agent. It exists in the form of two diastereomer racemates according to the configuration of the three chiral carbon atoms in the molecule, i.e. beta- or RRR/SSS and alpha- or RRS/SSR. The binary solid-liquid phase diagram of the two diastereomer racemates has been determined by differential scanning calorimetry (DSC). The two diastereomer racemates have different crystalline structures and are physical mixtures with an eutectic phase diagram. The eutectic mixture melts at 92.3 ± 1.0 °C and has alpha-TGIC content of 93.44% by mass or mole. With the help of the phase diagram the ratio of the two diastereomer racemates in TGIC may be determined. The binary phase diagram shows that beta-TGIC can be separated with efficiency from the mixture and may serve for enantiomer synthesis of high optical activity giving rise to the development of novel polymers.     

A novel spectrophotometric method for the simultaneous kinetic analysis of ternary mixtures by mean centering of ratio kinetic profiles

In this paper, a novel and very simple method was developed for the simultaneous spectrophotometric determination of ternary mixtures, without prior separation steps. The method is based on the mean centering of ratio kinetic profiles. The mathematical explanation of the procedure is illustrated. In order to investigate the applicability of the proposed method, it was applied to the simultaneous spectrophotometric determination of hydrazine, phenylhydrazine and acetylhydrazine based on their condensation reactions with p-(dimethylamino)benzaldehyde (DAB) and p-nitrobenzaldehyde (NB) in micellar sodium dodecyl sulfate (SDS) media as a typical ternary mixture. The analytical characteristics of the method such as accuracy, precision, relative standard deviation (R.S.D.) and relative standard error (R.S.E.) were calculated.     

Mixed micellization of gemini surfactant with nonionic surfactant in aqueous media: a fluorometric study

Herein we report on the study of the interactions between alkanediyl-α,ω-type cationic dimeric (gemini) surfactant and the nonionic Triton X-100 in aqueous medium. The critical micelle concentrations of binary mixtures were determined by fluorometric study. Using the regular solution theory for the analysis of the experimental data, the attractive nature of interactions and synergistic behavior of gemini surfactant and Triton X-100 mixture were demonstrated. The micelle aggregation number was measured using steady state fluorescence quenching method. The micropolarity, binding constant and dielectric constant of mixed systems were determined from the ratio of peak’s intensity (I ₁/I ₃) in the pyrene fluorescence emission spectrum.     

Novel quercetin derivatives: synthesis and screening for anti-oxidant activity and aldose reductase inhibition

The direct acylation of quercetin (I) with 3-chloro-2,2-dimethylpropanoyl chloride (II) gives a complex reaction mixture. The synthesis of different acylated quercetin with from mono- to tetra-O-substituted functions was achieved in a simple procedure wherein the yield of isomers depended on the stoichiometric ratio of reagents. The crude reaction mixtures were analysed (LC-MS) and compared with the isolated products. Unambiguous structural characterisation of isomeric quercetin derivatives was confirmed by NMR analysis. In addition, the quercetin dimer can be obtained in a high yield in the simple procedure. The anti-oxidant activity and aldose reductase inhibition of the compounds were screened with the aim of providing bi-functional remedies to treat diabetic complications and other diseases where oxidative stress and the polyol pathway are key etiological factors.     

Countercurrent extraction separation of some platinum group metals. part II

Binary mixtures of Pt and Rh, Pt and Ir, Pd and Rh. and Pd and Ir were resolved by a countercurrent extraction technique. The metals were partitioned between an acidic aqueous phase containing potassium thiocyanate and an organic phase, n-tributylphosphate. Distribution coefficients were determined for each metal for a thiocyanate: metal mole ratio of 10 : 1 and 200 : 1 at pH values of 1, 2, 3, and 3.8. Optimum conditions for separations were determined to be a thiocyanate; metal mole ratio of 10 : 1 and a pH of 1. Under these conditions the K_d values tor Pd, Pt, Rh and Ir were 139, 62.3, 0.19 and 0.09 resp. Effective separations were achieved with each binary mixture on a Craig extraction apparatus utilizing less than 10 equilibrium stages. There was a 95% average recovery of each of the metals.     

Measurements of vapour-liquid equilibria,densities, viscosities and dielectric properties of cyclohexanone + triethylamine mixtures with respect to keto-enol tautomerism

Densities, ?, kinematic viscosities ν, refractive indices n_D referred to the sodium D-line, static relative permittivities ε, specific conductances κ and vapour-liquid equilibrium data for cyclohexanone + triethylamine mixtures have been determined at two temperatures. Excess properties of mixing calculated from these data indicate that in such mixtures considerable amounts of enol-amine associates are formed. The permittivity data indicate that the formation of associates is an exothermic process, which also has a marked influence on the thermodynamic excess properties of the mixtures. The enol-amine associates may undergo electrolytic dissociation. A common evaluation of static relative permittivities and specific conductances shows that for the mixture the conductance data are affected considerably by the formation of undissociated ion pairs in the sense of Bjerrum theory, especially at concentrations of the mixture where it is less polar. The conductance data are also influenced considerably by the fact that the ion pairs are solvated if the molar ratio of triethylamine exceeds 0.5.     

Grafting onto polyester fibres

The influence of graft-copolymerisation reaction between polyester fibres and mixtures of acrylamide (AAm) and acrylic acid (AA) monomers on zeta potential (ζ) of the grafted polymer has been studied. The polyester fibre was rendered amphoteric in nature due to the introduction of the AAm-AA graft mixtures in the substrate. The (?ζ) increased to a considerable extent at higher pH values of the streaming solution due to increased dissociation of -COOH groups of the AA graft component present in the mixture. With the decrease in pH on the acidic side, decrease in (?ζ) was brought about due to suppression of the dissociation of -COOH groups and increase in the protonation of -CONH₂ groups. It was observed that (?δζ/ΔpH) ratio serves as a measure of the amphoteric character of the polymer containing mixtures of AAm-AA graft.     

Monodisperse Poly (Styrene-co-Divinylbenzene) Particles (3.2 μm) with Relatively Small Pore Size as HPLC Packing Material

Monodisperse 3.2-μm porous poly(styrene-co-divinylbenzene) particles have been prepared by a new multistage polymerization procedure, so-called ‘modified seeded polymerization’. In the synthesis of the particles sufficient porosity was generated by use of a diluent mixture with relatively low viscosity. The use of relatively high diluent/seed latex ratio resulted in the formation of particles with an average pore size of 13 nm. The particles were used as column-packing material in HPLC and their performance was compared with that of larger particles (d _n = 7.8 μm) obtained by the same method. The SEC plot for the 3.2 μm particles showed that the proposed material was particularly suitable for separation of analytes in the molecular weight range 100–2000. In reversed-phase mode alkylbenzenes were separated with resolution >2 by use of a relatively small column (50 mm × 4.6 mm i.d.) packed with 3.2-μm particles. Theoretical plate numbers (TPN) in excess of 35 000 plates m^?1 could be achieved with benzene as analyte. Whereas the ratio of TPN determined with pentylbenzene to that determined with benzene was less than 0.7 for the 7.8-μm particles, the same ratio was 0.95 for the 3.2-μm particles. With the 3.2-μm packing material proposed no significant decrease in resolving power was observed when the mobile-phase flow rate was increased sevenfold.     

Enzymatic resolution of (±)-5-phenyl-4,5-dihydroisoxazole-3-carboxylic acid ethyl ester and its transformations into polyfunctionalised amino acids and dipeptides

Enantiomerically pure (5R)-(?)-5-phenyl-4,5-dihydroisoxazole-3-carboxylic acid ethyl ester was obtained via enzymatic resolution of the corresponding racemic mixture using a lipase from hog pancreas (PPL). The following reduction of the ester group to the corresponding alcohol and the oxidation of the latter led to (5R)-(?)-5-phenyl-4,5-dihydroisoxazole-3-carbaldehyde, and the reaction between this and Schöllkopf’s reagent, (2R)-(+)-2,5-dihydro-3,6-dimethoxy-2-isopropylpyrazine, gave mixtures of adducts with a good syn/anti ratio. The steric configurations of the major diastereoisomer were assigned on the basis of spectroscopic data and X-ray analysis. The subsequent controlled hydrolysis of the pyrazine ring led to β-(5-phenyl-4,5-dihydroisoxazol-3-yl)-serine methyl esters and the corresponding dipeptides with (R)-valine. Finally, reductive cleavage of the 4,5-dihydroisoxazole ring under hydrolytic conditions made it possible to obtain the corresponding polyfunctionalised dipeptides.     

Correlation of the formation constant of ferrocene-cyclodextrin complexes with dielectric properties of the aqueous DMSO solution

The host-guest interactions between ferrocene and α-cyclodextrin (α-CD), β-cyclodextrin (β-CD), Heptakis(2,6-di-O-methyl)-β-cyclodextrin (2-β-CD) and Heptakis(2,3,6-tri-O-methyl)-β-cyclodextrin (3-β-CD) in aqueous DMSO solution were studied by means of cyclic voltammetry. The complex formation constant K was determined in the solutions of various values of the relative permittivity ?_r of DMSO:water mixture. The dependence of K on dielectric properties of the mixtures ?_r for all type of cyclodextrin utilized was found. Furthermore, the dependence of K on the cyclodextrin type was also found. As an additional feature the different dependencies of the Gibbs energy of the complex formation, for different CDs on the volume ratio of DMSO, φ_DMSO were observed.     

The determination of molecular diffusion coefficients by the barometric method

The binary molecular diffusion coefficients D _AB of a vaporizing liquid in gases under atmospheric conditions were measured by the new simple barometric method. A change in the pressure of a vapor-gas mixture in a closed cell was determined as a function of time. Under experimental conditions, one can also find partial saturated vapor pressures of substances. The deviations of the coefficients D _AB obtained by the new procedure from the literature values were within the spread of the experimental data. The D _AB coefficients (absent in the literature) were measured for mixtures of acetone, ethyl acetate, carbon tetrachloride, difluoroethanol, and cis and trans isomers of perfluorodecalin with argon. The saturated vapor pressures were determined for difluoroethanol and cis-and trans-perfluorodecalins under argon.     

Photolysis of <Emphasis Type="Italic">meta</Emphasis>-azidophenol in water-organic mixtures

Photolysis of m-azidophenol (m-AP) in organic solvents and water-organic mixtures of various composition was studied using the methods of electronic spectroscopy. m-Azidophenol dissolved in water-organic mixtures was shown to form associates with solvent molecules, depending on the composition of the mixture. The nature of m-AP photolysis products and the rate of their formation are determined by the character of m-AP solvation in water-organic mixtures. In acetonitrile solution, a polymeric product is formed via the interaction of the phenol group with the nitrene of an adjacent m-AP molecule. An increase in the mole fraction of water in a water-acetonitrile mixture leads to a decrease in the yield of the polymeric product and an increase in the yield of the hydroxylamine derivative. In water-ethanol mixtures, the hydroxylamine derivative is the main product of photolysis.     

Mobilities of mixtures of ion isotopes in gas mixtures

It is shown how the mobility of a mixture of isotopes of the same ion species in a gas mixture can be obtained directly from mobility data of a single isotope of the ion and one isotope of each neutral species, for any gas temperature and ratio of the electrostatic field strength to the gas number density. This combination of the “aliasing” procedure for ion isotopes, Blanc’s Law for gas mixtures at low fields, and the extended Blanc’s Law at intermediate and high fields is tested by comparing values calculated from the mobilities of ⁷⁹Br^? in ²⁰Ne with those determined both experimentally and ab initio for various mixtures. It is so accurate that it obviates the necessity in future work of making measurements or calculations for more than one isotope of each ion and each neutral.     

Proton NMR probing of stoichiometry and thermodynamic data for the complexation of Na and Li ions with 15-Crown-5 in acetonitrile-nitrobenzene mixtures

Proton NMR was used to study the complexation reaction of Li⁺ and Na⁺ ions with 15-Crown-5 (15C5) in a number of binary acetonitrile (AN)-nitrobenzene (NB) mixtures at different temperatures. In all cases, the exchange between free and complexed 15C5 was fast on the NMR timescale and only a single population average ¹H signal was observed. The formation constants of the resulting 1:1 complexes in different solvent mixtures were determined by computer fitting of the chemical shift mole ratio data. There is an inverse relationship between the complex stability and the amount of AN in the solvent mixtures. The enthalpy and entropy values for the complexation reaction were evaluated from the temperature dependence of the formation constants. In all the solvent mixtures studied, the resulting complex is enthalpy stabilized but entropy destabilized. Finally, the experimental results were compared with theoretical ones that were obtained from molecular modeling methods. Based on our results, it is most probable that Li⁺-15C5 in solvent stays in a rather nesting complex form with greater LogK_f values, but Na⁺-15C5 forms a complete perching complex form with lower LogK_f values.