Search results for "reaction rate constant"
showing 10 items of 210 documents
Photocatalytic oxidation of acetonitrile in gas–solid and liquid–solid regimes
2005
Il programma NON mi ha consentito di scaricare il PDF di questo articolo. Se lo volete ditemi come inviarlo ABSTRACT Photocatalytic degradation of acetonitrile was carried out in both gas–solid and liquid–solid regimes using two commercial TiO2 catalysts (Merck and Degussa P25). For the gas–solid regime, a continuous annular photoreactor was used. The influence on photodegradation kinetics of the gas flow rate and concentrations of acetonitrile, oxygen, and water was investigated. Acetonitrile degradation products detected in the gas phase included carbon dioxide and hydrogen cyanide. The same photoactivity was exhibited in the presence and in the absence of water vapour. The liquid–solid reg…
Thermal Degradation of Green Asparagus Texture
2019
A cutting cell was developed to evaluate the texture of green asparagus by measuring its resistance to being cut with a wire. The cell was used in conjunction with a universal texturometer and improved on the single-point method of the Wilder fibrometer. Experimental conditions were determined for using the cell to measure the cutting resistance of asparagus subjected to different extents of heat treatment. Better discrimination between samples was obtained than with a Kramer cell. The fresh asparagus spears. were heated at temperatures between 70 and 100°C for different lengths of time and the kinetics of the degradation of texture was studied. A biphasic (two-component) behavior was obser…
Modeling for the active site nitrate reductase. Oxidation of the complex [MovO(O2CC(S) CH3Ph)2]− by nitrate and nitrite in methanol
1998
Abstract Under acid conditions the [MoVIO2(O2CC(S)CH1Ph)2]2 reacts with thiols to yield the monomeric [MoVO(O2CC(S)CH3Ph)2] and disulfide. The reduced complex [MoVO(O2CC(S)CH3Ph)2]− can react with NO3− and NO2− in a one-electron step yeilding respectively NO2 and NO and the original molybdenum (VI)-dioxo complex. The experimental pseudo-first-order rate constant with respect to the Mo(V) complex at 25°C was found to be kobs=2.3×10−4s−1 for NO3− and kobs=1.0×10−2 for NO2−. Oxo transfers to and from the substrate have been coupled to produce a catalytic system which turns over the reaction RSH+(No3− or NO2−)+H+a 1 2 [ RS ] 2 +( NO ] 2 or NO )+ H 2 O , in which thiols, NO1− and NO2− serve as a…
Photokinetic examination of (Z,E,E)-4,4′-distyrylazobenzene
1995
Abstract 4,4′-Distyrylazobenzenes demonstrate a photokinetic equilibrium and a superimposed thermal backward reaction in which the absorption coefficient of one of the partners in the equilibrium is principally unknown. Using the dependence of the photostationary state on the irradiation intensity, the photochemical quantum yields ϕ 1 A and ϕ 2 B were determined, as well as the thermal rate constant k , as a function of the irradiation and observation wavelengths. Experimental difficulties and the wavelength dependence of ϕ 1 A and ϕ 2 B are discussed.
Synthesis of pentafluorophenyl(meth)acrylate polymers: New precursor polymers for the synthesis of multifunctional materials
2005
Pentafluorophenyl acrylate and -methacrylate were polymerized using AIBN as a thermal initiator. The obtained polymers were soluble polymeric active esters that could be used for the preparation of multifunctional polymers. The reactivity of poly(pentafluorophenylacrylate) and poly(pentafluorophenylmethacrylate) towards primary and secondary amines, as well as alcohols was investigated in a quantitative way. Both poly(active esters) reacted satisfactorily with aliphatic primary and secondary amines but only low conversion was found in the case of aromatic amines. Conversions of only 30% were reached when poly(pentafluorophenylacrylate) was treated with one equivalent of alcohol under base c…
Kinetic Investigation on Metal Free Anionic Polymerization of Methyl Methacrylate Using Tetraphenylphosphonium as the Counterion in Tetrahydrofuran
1997
The anionic polymerization of methyl methacrylate using tetraphenylphosphonium triphenylmethanide as an initiator proceeds in a living manner even at room temperature. The rate constants of propagation were measured between -20 and +20 °C using a flow tube reactor. At 0 °C the reaction half-lives range from 0.3 to 1 s. The polymerization follows first-order kinetics with respect to monomer conversion (with a short induction period) and shows a linear dependence of the number-average degree of polymerization on conversion with high initiator efficiencies and narrow molecular weight distributions (M w /M n < 1.1). The dependence of the measured rate constants on the active center concentratio…
Proteolytic cleavage of soybean Bowman-Birk inhibitor monitored by means of high-performance capillary electrophoresis. Implications for the mechanis…
1996
The hydrolysis of the soybean Bowman-Birk inhibitor in the presence of catalytic amounts of bovine trypsin and the formation of the non-covalent enzyme-inhibitor complex with an equimolar amount of enzyme are monitored by means of high-performance capillary electrophoresis (HPCE). The inhibitor is cleaved in the trypsin-reactive and more slowly in the chymotrypsin-reactive subdomain. HPCE proves itself as the only reliable analytical tool to monitor these reactions in clear contrast to classical electrophoretic, chromatographic and enzymatic methods. The most efficient separation of the intact and the two active site cleaved forms of the inhibitor was achieved in borate buffer at pH 10.0. T…
On the behaviour of the (Z)-Phenylhydrazones of some 5-alkyl-3-benzoyl-1,2,4-oxadiazoles in solution and in the gas phase: kinetic and spectrometric …
2008
Abstract Rate constants, k A,R , for the rearrangement of the ( Z )-phenylhydrazones ( 1a – e ) of a series of 5-alkyl-3-benzoyl-1,2,4-oxadiazoles substituted at C(5) with linear alkyl chains of different length (from C 4 up to C 12 ) into the relevant 4-acylamino-2,5-diphenyl-1,2,3-triazoles ( 2a – e ) have been measured in dioxan/water in the base-catalyzed region (pS + 10.5–12.6). For each substrate log k A,R are linearly related to pS + . The significant decrease of the slopes of these straight lines (from 0.96 down to 0.78) upon increasing the length of the linear alkyl chain at C(5) and that of the reactivity (down to 14–26%) upon increasing the substrate concentration suggest a decr…
Pressure dependence in the methyl vinyl ketone + OH and methacrolein + OH oxidation reactions: an electronic structure study.
2005
High-level electronic structure calculations were carried out for the study of the reaction pathways in the OH-initiated oxidations of methyl vinyl ketone (MVK) and methacrolein (MACR). For the two conformers of MVK (called synperiplanar and antiperiplanar), the addition channels of OH to the terminal and central carbon atom of the double bond dominate the overall rate constant, whereas the abstraction of the methyl hydrogen atoms has no significant kinetic role. In the case of MACR, only the antiperiplanar conformer is important in its reactivity. In addition, the lower Gibbs free energy barrier for MACR corresponds to the aldehydic hydrogen abstraction reaction, which will be somewhat mor…
Environmentally relevant precursors of carbonyl sulfide in aquatic systems
1997
Seawater solutions of environmentally relevant organosulfur compounds, commercial humic acid (HA), and natural dissolved organic matter (DOM) were incubated with and without UV light in order to determine the carbonyl sulfide (COS) producing capabilities of these compounds. COS dark- and photo-production rate constants were determined for dilute solutions of the organosulfur compounds (μmol l−1) and HA/DOM (mg l−1). Dissolved COS was determined using a purge and cryogenic trap method followed by GC/FPD detection. COS was produced in considerable amounts both non-photochemically and photochemically from the reduced form of free acid of glutathione (GSH) and photochemically from cysteine (CYS…