Hydrochloride method for the determination of monomer in the polycondensation of esters of α-amino acids

Summary A method is proposed for determining the monomer in the polycondensation of esters of-amino acids. The accuracy of the method was to within 1–1.5%.     

Kinetics of the Thermal Decomposition of Magnesium Salicylate Powder in Air

IntroductionThe chelate complexes of salicylic acid with rareearth and alkali earth ions have attracted considerableattention because of their special antibacterial proper-ties[1—3].The study of the thermal degradation of metalsalicylates is of major int…     

Kinetics of peroxidase-catalyzed oxidation of quercetin in the presence of β-cyclodextrin

It is established that the rate of peroxidase-catalyzed oxidation of flavonoid quercetin is increased by 20% in the presence of macrocyclic complexing agent β-cyclodextrin. The comparison of the kinetic parameters of the indicated reaction in the presence and in the absence of β-cyclodextrin shows that its introduction does not significantly influence the specificity of the enzyme with respect to the reducing substrate (characterized as k _cat/K _M ratio), while the increase in the reaction rate does not depend on the duration of the incubation of quercetin with β-cyclodextrin. It is assumed that the increase of the reaction rate is associated with nonspecific interaction between β-cyclodextrin and quercetin oxidation product.     

Chemical Reactions and Kinetics of the Carbon Monoxide Coupling in the Presence of Hydrogen

The chemical reactions and kinetics of the catalytic coupling reaction of carbon monoxide to diethyl oxalate were studied in the presence of hydrogen over a supported palladium catalyst in the gaseous phase at the typical coupling reaction conditions. The experiments were performed in a continuous flow fixed-bed reactor. The results indicated that hydrogen only reacts with ethyl nitrite to form ethanol, and kinetic studies revealed that the rate-determining step is the surface reaction of adsorbed hydrogen and the ethoxy radical (EtO-). A kinetic model is proposed and a comparison of the observed and calculated conversions showed that the rate expressions are of rather high confidence.     

Kinetics and Thermodynamics of the Absorption of Hydrogen in β-titanium Alloys

A thermogravimetric method was applied to study the hydrogen uptake in the near-β-titanium alloy Ti 10 2 3 and the metastable β-titanium alloy Ti 21S. The tests were performed in H₂-He gas mixtures with various partial pressures of H₂ at temperatures between 600 and 800°C. Basic findings such as the decreasing solubility of H₂ with increasing temperature could be verified, and first information on the effects of surface conditions was gained. Thus, it could be shown that, despite the low atomic mass of hydrogen, thermogravimetry is an appropriate tool for investigation of the H₂/metal interactions of titanium alloys. This revised version was published online in July 2006 with corrections to the Cover Date.     

Molecular Organization of Reagents in the Kinetics and Catalysis of Liquid-Phase Reactions: XI. Manifestation of the Structure of Solution in the Kinetics of Water Addition to Isocyanate in Water–Dioxane Mixtures

Evidence for the structural effect of liquids associated by hydrogen bonds on the kinetics of molecular reactions was experimentally found. The kinetics of hydrolysis of (phenylaza)phenyl isocyanate in water–dioxane mixtures was studied at various temperatures and in the presence of structure-making and structure-breaking additives. The apparent order of reaction with respect to water concentration increased with temperature because of the partial breaking of the H-bond solution structure. It was found that the value of was affected by salt additives, for which positive (Et₄NCl) or negative (KI) hydration is typical. This hydration resulted in strengthening or partially breaking the H-bond structure of water, respectively. It follows from the kinetic data that the addition of 0.1 mol/l Et₄NCl was equivalent to a decrease in the solution temperature by 6 to 7°, whereas the addition of 0.1 mol/l KI was equivalent to an increase in the temperature by 5 to 6°. The effect of poly(ethylene oxide) additives (which stabilize the structure of water) on the value of was similar to the effect of the tetraethylammonium salt, which is characterized by positive hydration.     

Kinetics of the Ziegler-Natta Polymerization of 1-Octene——The Kinetics and Mechanism of the Induction period

The kinetics of the induction period in the polymerization of 1-octene catalyzed by Solvay TiCl3-alkyl aluminium was studied with a dilatometer. The induction period decreases as [TiCl3] and [M]0 increase and temperature rises. It was observed through a microscope that large catalyst particles broke up into small particles in the induction period. So a kinetic model was proposed which ascribes the induction period to the breaking up of catalyst particles under the effect of polymer, and the most of the experimental results can be explained on the basis of the model.     

Studies on the Kinetics of the FO CO Reaction

IntroductionAproposedcycleinvolvingtheFOradicalsisl:ThecontributionofthiscycletothecatalyticdestrUctionofozoneisdeterndnedbythefirststep.Thereaction(l)isalsothoughttobeapossiblesinkforatInosphericCO2.Baueretal.3gavearateconstantofl.24.lO-i3cm3/sforreaction(l),whichwasbelievedtobecorrectwithinafactorof2at9(X)-l4(X)K.Theactivationenergywasestimatedtobe46.OkJ/mol.Bedzhanyanetal.4reportedk<4xlO-"and<5xlO-l6cm3/sat3ooand55OK,respectively.Alowerbarrierofl3.8kJ/molcanbeextrapoIated.Francisco…     

CIDNP of Diecyl Peroxides Studies on the Kinetics of Decomposition of Diacyl Peiroxides Ⅷ in the Decomposition of Diacyl Peroxides

H CIDNP spectra recorded during the decomposition of aliphatic diacyl peroxides ((RCOO)2 R=n-C H (1),n-c5H11(2)) in ODCB in the presence of scavengers,such as I2C2H5I,(CH3)2CHI,and CH2=CHCH2 Br show multiplet effect for the scavenged products,RX(X=Br,I) and for disproportionation products,R-H.The reactionmechanism is discussed in terms of radical pair theory.     

Kinetics of the Electrocatalytic Oxidation of 2,2-Dimethylolpropionaldehyde

A new method of synthesis 2,2-dimethylolpropionic acid from 2,2-dimethylolpropionaldehyde was put forward. The electrochemical oxidation behavior of 2,2-dimethylolpropionaldehyde has been investigated on a Ti/SnO₂ + Sb₂O₄/PbO₂ electrode by cyclic voltammetry (CV) and stable polarization curves in sulfuric acid. The results showed that it was an irreversible reaction controlled by diffusion. The formation mechanism of 2,2-dimethylolpropionic acid in the sulfuric acid was then proposed and the transfer coefficients of the reaction were calculated. It was concluded that RCHO+ỌH_ads→RCHOỌH_ads was the rate-determining step in the electrolysis process. The rate of this step obtained from the assumed process agrees well with experiment.     

Kinetics and Mechanism of the Hydrolysis of Benzyl Ether Bonds in Aqueous–Organic Media

Russian Journal of Physical Chemistry A - Kinetic parameters (rate constant, energy of activation, and entropy of activation) of the acid-catalyzed hydrolysis of the benzyl ethers...