Polymerization of Methacrylamide Initiated by the Persulfate/Thiolactic Acid Redox System

The aqueous polymerization of methacrylamide initiated by the ammonium persulfate/thiolactic acid redox system has been studied at 35 ± 0.2°C. The rate of polymerization is governed by the expression, R_p + K_p [MAA] ^1.33 [TLA]^0.22 [ammonium persulfate]^0.6. The deviations from normal kinetics are discussed. A tentative mechanism of initiation is given. The temperature dependence of the rate of polymerization has been studied over the range 30–55°C. The overall activation energy of polymerization is 10.4 kcal/mole.     

Excess molar quantities of (a halogenated n-alkane + an n-alkane) A comparative study of mixtures containing either 1-chlorobutane or 1,4-dichlorobutane

Excess molar volumes V_m^E at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C₄H₉Cl + (1 ? x)n-C_lH_{2l + 2}}, and II: {x1,4-C₄H₈Cl₂ + (1 ? x)n-C_lH_{2l + 2}}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities C_{p, m}^E at constant pressure. V_m^E is positive for all mixtures in series I: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, V_m^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆} is small and S-shaped, the maximum being situated at x_max = 0.178 with V_m^E(x_max)/(cm³ · mvl^?1) = 0.095, and the minimum is at x_min = 0.772 with V_m^E(x_min)/(cm³ · mol^?1) = ?0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, V_m^E/(cm³ · mol^?1) is 0.458 for l = 10, and 0.771 for l = 14. The C_{p, m}^Es of series I are all negative and |C_{p, m}^E| increases with increasing l: at x = 0.5, C_{p, m}^E/(J · K^?1 · mol^?1) is ?0.56 for l = 7, ?1.39 for l = 10, and ?3.12 for l = 14. Two minima are observed for C_{p, m}^E of {x1,4-C₄H₈Cl₂ + (1 ? x)n-C₇H₁₆}. The more prominent minimum is situated at x′_min = 0.184 with C_{p, m}^E(x′_min)/(J · K^?1 · mol^?1) = ?0.62, and the less prominent at x″_min = 0.703 with C_{p, m}^E(x″_min)/(J · K^?1 · mol^?1) = ?0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (x_min = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7.     

Studies of redox polymerization. I. Aqueous polymerization of acrylamide by an ascorbic acid–peroxydisulfate system

The polymerization of acrylamide initiated by an ascorbic acid–peroxydisulfate redox system was studied in aqueous solution at 35 ± 0.2°C in the presence of air. The concentrations studied were [monomer] = (2.0–15.0) × 10^?2 mole/liter; [peroxydisulfate] = (1.5–10.0) × 10^?3 mole/liter; and [ascorbic acid] = (2.84–28.4) × 10^?4 mole/liter; temperatures were between 25–50°C. Within these ranges the initial rate showed a half-order dependence on peroxydisulfate, a first-order dependence on an initial monomer concentration, and a first-order dependence on a low concentration of ascorbic acid [(2.84–8.54) × 10^?4 mole/liter]. At higher concentrations of ascorbic acid the rate remained constant in the concentration range (8.54–22.72) × 10^?4 mole/liter, then varied as an inverse halfpower at still higher concentrations of ascorbic acid [(22.72–28.4) × 10^?4 mole/liter]. The initial rate increased with an increase in polymerization temperature. The overall energy of activation was 12.203 kcal/mole in a temperature range of 25–50°C. Water-miscible organic solvents depressed the initial rate and the limiting conversion. The viscometric average molecular weight increased with an increase in temperature and initial monomer concentration but decreased with increasing concentration of peroxydisulfate and an additive, dimethyl formamide (DMF).     

Spectrophotometric determination of oxalic acid in presence of glyoxylic acid and chloride

Glyoxylic acid gives a yellow 1:1 complex, [FeCHOCOO]²⁺ with iron(III). The dissociation contant, measured by two spectrophotometric methods, is K = 9.7 ± 1 mol l^?1. Oxalic acid gives two complexes with iron(III) which absorb in the same range around 400 nm. With appropriate precautions and corrections, oxalic acid concentrations of about 10^?1–10^?2 M can be determined in the presence of glyoxylic acid and chloride.     

In Situ Biphasic Extractive Fermentation for Hexanoic Acid Production from Sucrose by Megasphaera elsdenii NCIMB 702410

Hexanoic acid production by a bacterium using sucrose as an economic carbon source was studied under conditions in which hexanoic acid was continuously extracted by liquid–liquid extraction. Megasphaera elsdenii NCIMB 702410, selected from five M. elsdenii strains, produced 4.69 g l^?1 hexanoic acid in a basal medium containing sucrose. Production increased to 8.19 g l^?1 when the medium was supplemented by 5 g l^?1 sodium butyrate. A biphasic liquid–liquid extraction system with 10 % (v/v) alamine 336 in oleyl alcohol as a solvent was evaluated in a continuous stirred-tank reactor held at pH 6. Over 90 % (w/w) of the hexanoic acid in a 0.5 M aqueous solution was transferred to the extraction solvent within 10 h. Cell growth was not significantly inhibited by direct contact of the fermentation broth with the extraction solvent. The system produced 28.42 g l^?1 of hexanoic acid from 54.85 g l^?1 of sucrose during 144 h of culture, and 26.52 and 1.90 g l^?1 of hexanoic acid was accumulated in the extraction solvent and the aqueous fermentation broth, respectively. The productivity and yield of hexanoic acid were 0.20 g l^?1 h^?1 and 0.50 g g^?1 sucrose, respectively.     

Photopolymerization of methyl methacrylate using triethylamine-nitrobenzene complex as photoinitiator

Photopolymerization of methyl methacrylate in bulk and in solution at 40° using triethylamine nitrobenzene (TEA-NB) complex as photoinitiator was studied kinetically. Initiator order x, given by the relation R_pα([TEA][NB])^x, was 0.28 for [TEA][NB] < 25 × 10 ^?8 mol² · l^?2; for higher values of [TEA][NB], x was practically zero. Monomer order was 1.1 in benzene and pyridine but much less than unity (0.65–0.70) in carbon tetrachloride and chloroform. Kinetic analysis indicated that the initiation process was monomer and solvent dependent. The halomethane solvents enhanced the polymerization rate through their active participation in the initiation or radical-generation steps. End-group analysis indicated incorporation of basic (amino) end-groups in the polymers. The kinetic non-ideality was explained on the basis of significant initiator-dependent termination through primary radicals or via degradative transfer to initiator.     

Volumetric properties of a stoichiometric mixture of K+ and Br− ions in H/D isotope-substituted aqueous-methanolic solutions between 278.15 and 318.15 K: II. H2O-CD3OH-KBr and D2O-CH3OD-KBr systems

The magnetoflotation densities of potassium bromide solutions in H₂O-CD₃OH and D₂O-CH₃OD mixtures are measured using, with an error of at most ±(1.0 × 10^?5) g/cm³ for methanol mole fractions x ₂ of 0.06, 0.1, 0.3, or 0.6; and for the potassium bromide mole fractions up to about 2.65 × 10^?2 at 278.15–318.15 K in 10-K steps. The limiting partial molar volumes $\bar V_3^\infty $ of a stoichiometric [K⁺ + Br^?] mixture and the corresponding H/D isotope effects are calculated. The key role in the volumetric effects of salt solvation is played by the interactions between bromide ions and molecules of the mixed solvent, resulting in hydrogen-type bonding.     

Pulse radiolysis studies of intermolecular charge transfers involving tryptophan and three-electron-bonded intermediates derived from methionine

The oxidation processes of the radiation-generated, three-electron-bonded intermediates AcMet₂ [S??S]⁺ and AcMet [S??Br] were investigated by pulse radiolysis via their reactions with tryptophan (TrpH). These intermediates were derived from N-acetyl-methionine amide (N-AcMetNH₂) and N-acetyl-methionine methyl ester (N-AcMetOMe). The bimolecular rate constant k of the reaction between each intermediate and l-tryptophan (TrpH) was measured. For N-AcMetNH₂, k for the reaction of AcMet₂ [S??S]⁺ with TrpH were 3.4?×?10⁸ and 2.2?×?10⁸?dm³?mol^?1?s^?1 at pH?=?1 and 4.5, respectively. For N-AcMetOMe, k for the reaction of AcMet₂ [S??S]⁺ with TrpH were 4.0?×?10⁸ and 2.8?×?10⁸?dm³?mol^?1?s^?1 at pH 1 and 4.5, respectively. The rate constants for the intermolecular transformation of Met [S??Br] into TrpH⁺ or Trp were also estimated. For N-AcMetNH₂, k for the reaction of AcMet₂ [S??Br] with TrpH were 2.6?×?10⁸ and 3.3?×?10⁸?dm³?mol^?1?s^?1 at pH 1 and 4.5, respectively. Related mechanisms were discussed.     

Automated determination of carboxylic acids in biological and geochemical samples by means of a chemical reaction detector

Rapid evaluation of carboxylic acids by means of an automated spectrophotometric determination in a continuous-flow system is described. The system was applied to food and soil extracts either as a stand-alone device or as a chemical reaction detector coupled to a chromatographic separation column. Calibration in the automated system was performed with citric acid as a reference standard in the concentration range 4.76 × 10^?5?4.76 × 10^?3 mol l^?1. The molar calibration equation was A=64x ? 6.7 × 10^?5 (x=concentration ) with a correlation coefficient of 0.9997 ( six points). The sample volume was 0.5 ml. In addition to the semi-quantitative evaluation of carboxylic groups, it is shown that the system is also applicable to species analyses.     

Preparation and ionic conductivity of (100−x)(0.8Li2S·0.2P2S5)·xLiI glass–ceramic electrolytes

The glass–ceramic electrolytes of (100?x)(0.8Li₂S·0.2P₂S₅)·xLiI (in mole percent; x?=?0, 2, 5, 10, 15, 20, and 30) were prepared by mechanical milling and subsequent heat treatment. Crystalline phases analogous to the thio-LISICON region II or III in the Li₂S–GeS₂–P₂S₅ system were precipitated. The thio-LISICON III analog phase was mainly precipitated at the composition x?=?0, and the thio-LISICON II analog phase was precipitated in the composition range from x?=?2 to 15. The X-ray diffraction peaks of the thio-LISICON II analog phase shifted to the lower diffraction angle side with increasing the LiI content. High conductivities above 2?×?10^?3?S?cm^?1 at room temperature were observed in the glass–ceramics at the wide composition range from x?=?2 to 15. The glass–ceramic electrolyte at x?=?5 with the highest conductivity of 2.7?×?10^?3?S?cm^?1 showed a wide electrochemical window of about 10 V. The addition of LiI to the 80Li₂S·20P₂S₅ (in mole percent) glass was effective in crystallizing the thio-LISICON II analog phase with high conductivity from the glass.     

Polymerization of Acrylonitrile Initiated by 1,4-Dimethyl-1,4-bis(p-nitrophenyl)-2-tetrazene

The polymerization of acrylonitrile (AN) initiated by 1,4-dimethyl-1,4-bis(p-nitrophenyl)-2-tetrazene (Ie) was studied in dimethylformamide (DMF) at high temperature. The polymerization proceeds by a radical mechanism. The rate of polymerization is proportional to [Ie]^0.64 and [AN]^1.36. The overall activation energy for the polymerization is 21.5 kcal/mole within the temperature range of 115-130°C. The chain transfer of Ie was also undertaken over the temperature range of 120-135°C. The activation parameters for the decomposition of Ie at 120°C are k_d = 2.78 × 10^?6 sec^?1, ΔH^? = 40.8 kcal/mole, and ΔS^? = 19.5 cal/mole-deg, respectively.     

Elektrometrische Untersuchungen über die Ag2S-Bildungsgeschwindigkeit in ammoniakalischen Lösungen von Ag+-Ionen mittels Thioacetamid, 5. Mitt.

On basis of polarographic method of continuous registration at constant potential, the quantitative investigation of the rate of Ag₂S formation by thioacetamide (TAA) was performed and, the following equation for the reaction rate between Ag⁺-ions andTAA in ammoniacal solutions has been derived: 1 $$ - \frac{{d[Ag^I ]}}{{d t}} = k \cdot \frac{{[Ag^I ] \cdot [CH_3 CSNH_2 ]^{1/4} }}{{[H^ + ]^{1/10} }} \cdot \frac{{fAg}}{{f_H^{1/10} }}$$ The value, at 25.0^o, of the rate constantk is (6.8±0.4)· ·10^?2 mole^?3/20·litre^3/20·sec^?1. The validity of equation (1) has been proved over the pH range 8.3–10.8 and the ammonia concentration of 5.6·10^?2–1.0 mole per litre, by only a small excess ofTAA and moderate reaction rates.     

Kinetics and mechanism of the reduction of μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] by dithionate ion

The kinetics and mechanism of the reduction of the μ-adi-di[N,N′-bis{salicylideneethylenediaminatoiron(III)}] complex, [Fe₂adi], by dithionate ion, S₂O₆ ^2?, have been investigated in aqueous perchloric acid at 29 °C, I = 0.05 mol dm^?3 (NaClO₄) and [H⁺] = 5.0 × 10^?3 mol dm^?3. Spectrophotometric titrations indicated that one mole of the reductant was oxidized per mole of oxidant. Kinetic profiles indicated first-order rate with respect to [Fe₂adi] but zeroth-order dependence on [S₂O₆ ^2?]. The rate of reaction increased with increase in [H⁺], decreased with increased dielectric constant, but was invariant to changes in ionic strength of the medium. Addition of small amounts of AcO^? and Mg²⁺ ions did not catalyse the reaction. A least-squares fit of rate against [H⁺]² was linear (r ² = 0.984) without intercept. The reaction was analysed on the basis of a proton-coupled outer-sphere electron transfer mechanism.     

Complexation and extraction behavior of trivalent indium with multiple proton ionizable p�Ct-butylcalix[5]arene pentacaarboxylic acid derivative: a new efficient solvent extraction reagent for indium

Complexation behavior of plural ion-exchangeable p?Ct-butylcalix[5]arene pentacarboxylic acid derivative towards trivalent indium has been investigated along with its monomeric analog from weakly acidic media into chloroform. The cyclic structure of calixarene ligand providing certain cavity and cooperativity of functional groups significantly affect the complexation behavior and calixarene derivative is an excellent extractant over monomeric analog. The extraction mechanism is ion exchange and carboxylic acid groups are adequate functional sites for extraction. Mononuclear and/or polynuclear species of indium and monomeric or bridged dimeric species of calixarene are involved in complexation and the composition of extracted complex varied with solution pH. One mole of calix[5]arene derivative tend to extract 3.5 mol of indium. The loaded indium was quantitatively back extracted with 1 mol dm^?3 hydrochloric acid solution.     

Detailed Mechanism of Phenol-Inhibited Peroxidase-Catalyzed Oxidation of Indole-3-Acetic Acid at Neutral pH*

The inhibition of horseradish peroxidase (HRP)-cata-lyzed oxidation of indole-3-acetic acid (IAA) by a phenol, caffeic acid (CA), was studied using both a kinetic approach and computer simulation. The presence of CA resulted in a lag period in IAA oxidation. The lag period increased slowly with increasing [CA] until a critical concentration, [CA]_cr, was reached, then it increased much faster when [CA] was greater than [CA]_cr. The [CA]_cr was proportional to [IAA] and did not depend upon [HRP]. Caffeic acid was oxidized by compound I and compound II of HRP with bimolecular rate constants (6.8 ± 10⁷ and 2.1 ± 10⁷M-¹s^?l), which were much higher than the corresponding rate constants for IAA oxidation (2.3 ± 10³ and 2.0 ± 10²M^?1s^?1). Our experimental data show that CA inhibits IAA oxidation because it is able to compete effectively as a peroxidase substrate. A model based on a detailed mechanism of IAA oxidation was investigated using computer simulation. A rate constant driving nonenzymatic hydroperoxide formation in IAA solution was determined, 3.0 × 10^?-⁷ s^?1. The model quantitatively describes the experimental results of this work and also qualitatively explains data published earlier. The critical inhibitor concentration is approximately equal to twice the concentration of hydroperoxide in IAA solution at the time of inhibitor addition. Therefore hydroperoxide Concentration can be calculated from the determination of critical inhibitor concentration.     

Raman study of halogen exchange equilibria in low melting mixtures consisting of sodium tetrachloroaluminate and tetrabromoaluminate

The halogen-redistribution reactions between [AlCl₄]^? and [AlBr₄]^? in molten mixtures of NaAlCl₄ and NaAlBr₄ with widely varying mole ratios have been studied by Raman spectroscopy at 160–300°C and the melting points have been measured. By monitoring the intensities of the totally symmetric stretching a₁-modes of both the parent tetrahalides as well as those of the mixed halides [AlCl₃Br]^?, [AlCl₂Br]^? and [AlClBr₃]^? it is concluded that the mixtures equilibrate very fast and consist of an almost random distribution of the five species. NaAlCl₄ and NaAlBr₄ form an eutectic mixture with a molar ratio near to 4:1, with a melting point of ca 142°C.     

Quantum yield for photosubstitution of a co group in chromium hexacarbonyl by pyridine

The quantum yield of the photosubstitution of CO by pyridine in cyclohexane has a value of 0.67 ± 0.02 for [Cr(CO)₆] = 3.10^?4 mol l^? and [pyridine] = 10^? mol l^?1.     

CZE and ESI-MS of Borate-Sugar Complexes

Capillary zone electrophoresis (CZE) with electrospray ionization (ESI) mass spectrometry (MS) was used to study borate (B^?1) and sugar (L) complexes (L _x B^?1). Boric acid was adjusted to pH 10 with ammonium hydroxide to create an ESI-MS compatible CZE background electrolyte. We show for the first time that the electrophoretic peaks for each injected sugar contained both the substrates (i.e., sugar and/or multimers) and products (i.e., L _x B^?1). The effects of sheath liquid, temperature, and borate concentration were studied. The molecular mass information obtained from the ESI-MS provided new evidence on the mechanisms of borate-sugar complexation. Direct infusion ESI-MS and CZE-ESI-MS experiments strongly suggest that the formation of L _x B^?1 was from the direct reaction of a sugar or sugar multimer (L _x ) and B^?1. Larger L _x B^?1, where x > 2 were observed. Separation in the CZE dimension allows for the simultaneous analysis of a sugar mixture and simplified the ESI-MS analysis of sugars of the same molecular mass. The increase in sugar electrophoretic mobility caused by the increase in borate concentration was discussed in terms of the formation of L _x B^?1 complexes. In addition, the separation of five nucleosides by CZE using a borate electrolyte and detection using ESI-MS is demonstrated.     

Molecular Zeeman effect of 3-oxetanone and 3-methylene oxetane,and the comparison of the magnetic-susceptibility anisotropies,molecular quadrupole moments,and other magnetic parameters with other four-membered rings

The molecular Zeeman effect is reported for 3-oxetanone and 3-methylene oxetane at fields near 20000 G. The results for 3-oxetanone are molecular g-values: g_aa = ?0.1059 ± 0.0008, g_bb = ?0.0581 ± 0.0004,g_cc = ?0.0437 ± 0.0004, magnetic susceptibility anisotropies:2x_aa -x_bb - x_cc = (9.6±0.5) x 10^?6 erg/G²mole, 2x_bb - x_aa - x_cc = ?(7.8±0.6) x 10^?6 erg/G²mole, and molecular quadrupole moments: Q_aa = ?(12.8±0.8) x 10^?26 esu cm,Q_bb = (7.9±0.8) x 10^?26 esu cm, and Q_cc = (4.9±0.8) x 10^?26 esu cm. For 3-methylene oxetane, the results are g_aa = ?0.0510 ± 0.0018, g_bb = ?0.0435 ± 0.0010, g_cc = ?0.0313 ± 0.0010, 2x_aa - x_bb - x_cc = ?(10.9±0.5) x 10^?6 erg/G² mole, 2x_bb - x_aa - x_cc = (2.3±0.9) x 10^?6 erg/G² mole, Q_aa = -?5.4±1.0) x 10^?26 esu cm, Q_bb = (5.1 ± 1.2) x 10^?26 esu cm, and Q_cc = (0.2±1.5) x 10^?26 esu cm. The bulk magnetic susceptibility for 3-oxetanone was measured to be x = 1/2 (x_aa+x_bb+x_cc) = ?(30.6±1.5) x 10^?6 erg/G² mole. The out-of-plane minus average in-plane magnetic-susceptibility anisotropies in four-membered rings show larger paramagnetism than predicted on the basis of localized group susceptibility anisotropies. This effect is discussed and a possible explanation presented.     

Determination of Benzoyl Peroxide Levels in Wheat Flour and Pharmaceutical Preparations by Differential Pulse Voltammetry in Nonaqueous Media

Abstract

Benzoyl peroxide (BP) was determined by differential pulse voltammetry (DPV) using a glassy carbon electrode in a dichloromethane‐acetic acid (1.5×10^?2 mol l^?1) solution and tetrabutyl ammonium perchlorate (0.01 mol l^?1) as the supporting electrolyte. The peak potential was ?0.045 V (vs. Ag/AgCl). There was a good linear relationship between the peak current and the benzoyl peroxide concentration in the range of 2.5×10^?6–1.0×10^?4 mol l^?1. The detection limit of the method was 2.5×10^?7 mol l^?1. The recovery was 94.8–106.0%. The samples of wheat flour and the pharmaceutical preparations for the treatment of acne vulgaris were directly detected with desired results. The reaction mechanism of benzoyl peroxide on the electrode was also discussed, which was two electrons and two protons irreversible reaction.