Studies on Kinetics of Chlorination Reaction of Polyethylene

Through kinetic method, the reaction mechanism and the rate equations of chlorination of polyethylene are suggested in this paper. The rate of chlorination is second order with respect to the concentration of methylene remained and chlorine, respectively. Apparent changes in crystallinity during chlorination processes were determinated by differential scanning calorimetry(DSC). The mathematical model relating crystallinety with kinetic parameters and function of sequence length distribution are derived.     

STUDIES OF UNUSUAL OXIDATION STATES OF TRANSITION METALS (Ⅰ)——KINETICS AND MECHANISM OF OXIDATION OF POTASSIUM THIOCYANATE BY DIPERIODATOARGENTATE(Ⅲ) ION IN ALKALINE MEDIUM

The kinetics of oxidation of potassium thiocyanate by diperiodatoargentate (Ⅲ) (DPA) ions was studied in aqueous alkaline medium ([OH~-]=7.00×10~(-3)—0.200 mol. dm~(-3)) at a constant ionic strength (μ=0.30 mol. dm~(-3)). It is found that the reaction order in DPA is unity. The dependence of the rate on [OH~-] implies that there are two pathways through which the reaction proceeds. In each pathway, the order in NCS-is fractional and the kinetic data fit well in with Michaelis-Menten process. The influence of ligand on the reaction is examined and the reactive species are inferred. Two pathways of inner-sphere two-electrons transfer are believed to be involved in the oxidation. The rate equations are derived and all the equilibrium constants and rate constants are evaluated. Activation parameters of one pathway are determined.     

Density Functional Study on the Reaction Mechanism for the Reaction of Ni^＋ with Ethane

The mechanism of the reaction of Ni^ (^2D) with ethane in the gas-phase was studied by using density functional theory.Both the B3LYP and BLYP functionals with standard all-electron basis sets are used to give the detailed information of the potential energy surface (PES) of [Ni,C2,H6]^ . The mechanisms forming the products CH4 and H2 in the reaction of Ni^ with ethane are proposed.The reductive eliminations of CH4 and H2 are typical addition-elimination reactions.Each of the two reactions consists of two elementary steps:C-C or C-H bond activations to form inserted species followed by isomerizations to from product-like intermediate.The rate determining steps for the elimination reactions of forming CH4 and H2 are the isomerization of the inserted species rather than C-C or C-H bond activations .The elimination reaction of forming H2 was found to be thermodynamically favored compared to that of CH4.     

The effects of ultrasound frequency and power on the activation energy in Si-KOH reaction system

The activation energy is the minimum amount of energy required to initiate a reaction. It is one of the important indexes for appraising a reaction. The chemical reaction rate is closely related to the value of activation energy, and reducing activation energy is propitious to promoting a chemical reaction. In the present paper, the relationship between the activation energy in Si-KOH reaction system and the ultrasound frequency and power has been discussed for the first time. The range of ultrasound frequency and power is 40-100kHz （interval by 20kHz） and 10-50W （interval by 10W）, respectively. The experimental clata indicate that the activation energy decreases with the increasing ultrasound power. Comparing with the activation energy without ultrasound irradiation, the results in our paper indicate that ultrasound irradiation could reduce the activation energy in Si-KOH reaction system and increase the reaction rate.     

In-situ copolymerization of aniline with alkyl amine by APS： Kinetics and application

The kinetic study of in-situ eopolymerization of aniline with o- and p-methylaniline by ammonium persulfate （APS） has been carried out. UV-vis spectroscopic method was used to investigate the course of copolymerization. Structural characterization was studied by PT-IR spectral analysis. The electronic spectra of the copolymers poly（aniline-co-p-toluidine） and poly（aniline-co-o- toluidine） show blue shift. The shift has been observed in the bands corresponding to π→π^＊ transition as well as in the exciton transition. The increase in absorbance recorded during the reaction for different concentration of aniline, o- and p-toluidine at various intervals of time of polymerization reaction indicates a growth in the polymer formation. The resulting first-order rate constant was used to calculate the rate of copolymer formation using the rate equation -d[A]/dt = kc^n.     

Studies of Unusual Oxidation States of Transition Metals Ⅱ——Kinetics and Mechanism of Oxidation of Pyruvate by Diperiodatoargentate (Ⅲ)Ion

The kinetics of oxidation of pyruvate by diperiodatoargentate( III) ion (DPA) has been studied spec-trophotometrically in alkaline medium. It was found that the reaction order with respect to both DPA and pyruvate is unity and the rate equation can be expressed asThe rate increases with the increase in [OH ] and decreases with the increase in [periodate]. There is a positive ionic strength effect in this reaction system. A mechanism has been proposed to explain the experimental results. The observed activation parameters are presented.     

A Facile and Efficient Oxidation of α,β-Unsaturated Alcohols with Manganese Dioxide in Ionic Liquids under Mild Conditions

The oxidation of α,β-unsaturated primary and secondary alcohols to corresponding aldehydes and ketones by manganese dioxide in ionic liquids as a safe recyclable and accelerative reaction medium under mild conditions are described. The rate of the oxidation reaction is faster and the yield is higher than that with conventional procedures.     

Theoretical studies of the reactions of O(~3p) with halogenated methyl (Ⅰ)——Reaction mechanism of the O(~3p) CH_2Cl reaction

The reaction of O(~3P) with CH_2Cl radical has been studied using ab initio molecular orbital theory. G2 (MP2) method is used to calculate the geometrical parameters, vibrational frequencies and energies of various stationary points on the potential energy surface. The reaction mechanism is revealed. The addition of O(~3P) with CH_2Cl leads to the formation of an energy rich intermediate OCH_2Cl which can subsequently undergo decomposition or isomerization to the final products. The calculated heat of reaction for each channel is in agreement with the experimental value. The production of H CHClO and Cl CH_2O are predicted to be the major channels. The overall rate constants are calculated using transition state theory on the basis of ab initio data. The rate constant is pressure independent and exhibits negative temperature dependence at lower temperatures, in accordance with the experimental results.     

Appraisal of an oligomerization behavior of unprotected carbohydrates induced by phosphorus reagent

In this article, a novel oligomerization behavior of unprotected monosaccharides was discovered in a one-pot reaction induced by phosphorus reagent at room temperature. The inherent characteristics of the oligomerization reaction were dissected in detail by mass spectrometry based method combined with NMR technology. It was found that the main glycosidic bonding pattern is (1→6) linkage with 66% regioselectivity for each step. The ratio of α-(1→6) and β-(1→6) glycosidic bonds formed is around 1:1. The reactivity of 1-OH group from aldoses and the driving force from penta-coordinated phosphorus intermediates are the two critical factors for the oligomerization, according to the monitoring experiments by ESI-MS and NMR. Besides, the oligomerization reaction has good compatibility for various aldoses and could expand to O-glycosylated modification of peptides in vitro. The above results will provide a novel enlightenment to develop more convenient and higher-efficient methods for the synthesis of oligosaccharide library.     

A COMPARISON OF DENATURATION AND INACTIVATION RATES OF CREATINE KINASE IN GUANIDINE SOLUTIONS

Both the denaturation, as followed by UV absorbance and fluorescence changes, and inac-tivation of creatine kinase in guanidine solutions have been found to be first order reactions.In 3 M guanidine, at 30℃, the inactivation rate constant was found to be 5.9 sec~(-1) and thedenaturation rate constant 1.9 sec~(-1). At lower guanidine concentrations, the inactivation rateconstants were only little affected whereas the denaturation rate constants decreased markedly,being of the order of 0.04 in 1 M and 0.004 in 0.5 M guanidine. The kinetics of the inactiva-tion reaction in 0.5 M guanidine was found to be in agreement with a combination of two firstorder reactions. The enzyme lost activity first by a fast reaction with a rate constant onlyslightly lower than the rate constant in 3 M guanidine followed by a slower reaction with a rateconstant of 0.003 sec~(-1). In 0.3 M guanidine, very little change in either UV absorbance or influorescence was observed, but, in sharp contrast, the enzyme lost considerable activity by a fastreaction and this was followed by a slower reaction of inactivation. Even after prolongeddenaturation in 0.5 and 0.3 M guanidine, residual activities of 3.4% and 30% remained res-pectively. The above results suggest a very fragile active site although dissociation of thedimer and reversible guanidine inhibition may also contribute to the initial rapid inactiva-tion. It is also to be noted that the multiphasic courses of inactivation at lower guanidineconcentrations seem to suggest the presence of partly active intermediates during denaturation.     

Melamine–formaldehyde resins: Constitutional characterization by fourier transform 13C-NMR spectroscopy

The random chemical structures of melamine–formaldehyde resins, including methylated melamine–formaldehyde resins and urea–melamine formaldehyde resins, were investigated by ¹³C-NMR spectroscopy (Fourier transform). All the combined formaldehydes, methylol and methyl ether groups, methylene structures, and dimethylene ether structures were assigned. A ¹³C chemical shift of methylene carbon occurred by substitution of other constituents of the methylene group for a proton of the adjacent monosubstituted nitrogen atom, as shown in a ¹³C-NMR spectrum of urea–formaldehyde resins. It was found that the chemical shift of each corresponding carbon of both melamine resins and urea–melamine resins was almost superimposed with that of urea resins.     

Fragmentation of peptides with N-terminal dimethylation and imine/methylol adduction at the tryptophan side-chain

The reaction between formaldehyde and the side-chain of tryptophan results in a methylol adduct. This methylol adduct formation also occurs during reductive methylation reactions. In the current study, we investigate the fragmentation pattern of peptides with N-terminal dimethylation and methylol adduction at the tryptophan side-chain. Once formed, the methylol group can easily undergo water loss to form an imine. The peptides with imine or methylol adduct on tryptophan exhibit similar MS/MS fragmentation patterns. We observed ions resulting from an intramolecular reaction between the dimethylamino group at the peptide N-terminus or the lysine side-chain and the imine group. This reaction reduces the imine to a methyl group. We also observed the loss of the imine adduct on tryptophan. This reaction is likely to occur through the reaction of an amino or hydroxyl group with the imine adduct followed by subsequent loss of methylenimine or formaldehyde.     

The Initial Stage of the Reaction of Melamine with Formaldehyde

The concentration-time relationships of the individual active species in the oligocondensation stage of the reaction of melamine with formaldehyde have been investigated, mainly by electrochemical methods. Based on the reaction equations, a kinetic model of the overall reaction was established and the rate constants were calculated by numerical methods. The results suggest the hydroxy-methylamines are converted to methylene and dimethylene ether bridged compounds by acid- and base-catalyzed reactions, respectively. At pH 7-10 the formation of methylene bridges by base-catalyzed scission of dimethylene ether bridges may occur.     

A阶苯基二氨三嗪-甲醛树脂的结构表征

本文通过化学分析和VPO对数均分子量的测定讨论了A阶苯基二氨三嗪-甲醛树脂的组成和结构,对其H-NMR波谱做了解析,用液相色谱技术测定了树脂中各分子物种的含量。     

聚丙烯酰胺的改性和表征

用甲醛(F)和二氰二胺(D)改性聚丙烯酸胺(PAm),制得新型阳离子聚电解质PAm·MG,对PAm·MG的合成和表征进行了研究。合成反应通过两步进行,先使PAm与F反应,生成羟甲基化产物PAm·M,然后在酸性条件下使PAm·M与D反应,制得PAm·MG.控制F用量,得到不同取代度的PAm·M.和PAm·MG。PAm·MG在水溶液中能与阴离子聚电解质形成复合物沉淀证明PAm·MG带有阳离子基团。元素分析及电位、浊度滴定结果表明PAm·M中的羟基完全与D发生了反应。SALLS测得的M_w证实了PAm在改性过程中分子链未发生降解。     

Acid-catalyzed hydroxymethylation of benzamide with formaldehyde

Hydroxymethylation of benzamide with formaldehyde was investigated in the pH regions of 0.6–6.7 by use of the sulfite method. Investigation of the dependence of the second-order rate constant of the hydroxymethylation k on pH revealed that k decreased with increasing acidity from pH 6.7, became approximately constant at pH 4.5–5.5 (minimum rate), and then increased with increasing acidity. The rate equation showing the pH dependence of k was drawn from the reaction mechanism, and theoretical curves denoting this rate equation and the corresponding observed curves were compared. It was found that the hydroxymethylation is a reaction between a molecule of benzamide and the conjugate acid of formaldehyde (methylol cation) in the region below ca. pH 2.5, and the parallel reaction of a molecule of benzamide with methylol cation and a molecule of formaldehyde (HCHO) in the pH region of 2.5–4.0; in the region of ca. pH 4.5–5.5 the reaction is that between a molecule of benzamide and a molecule of formaldehyde, and the reaction in the pH region 5.5–6.7 is a parallel reaction of a molecule of formaldehyde with the conjugate base and a molecule of benzamide.     

Improvement of thermal stability of sulfonated polyphosphazenes by introducing a self‐crosslinkable group

We prepared sulfonated polyphosphazenes having various aryloxy substituents, and studied their thermal stabilities and membrane properties. Sulfonated polyphosphazenes were synthesized by the reaction of polydichlorophosphazene with sodium aryloxides and subsequent sulfonation with fuming sulfuric acid. With increasing the degree of sulfonation, the polymers showed higher proton conductivity, but suffered more from swelling in an aqueous solution. We introduced a hydroxymethylphenoxy group onto the phosphazene backbone as a self‐crosslinkable group by reaction of poly(dichlorophosphazene) and a sodium salt of 4‐hydroxymethylphenol. When a film of a sulfonated polymer having a methylol group was heated at 80 °C under vacuum for 1 h, it became insoluble in NMP, indicating the formation of a network structure. We investigated the crosslinking reaction of the polymers by DSC and FTIR. The crosslinking reaction proceeded only in the sulfonated polymers. Because the sulfonated polymers provide acidic protons, the methylol groups became more electrophilic and reacted with neighboring aromatic rings. A condensation reaction between themselves could also occur. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5850–5858, 2008     

Semimicro Size Exclusion Chromato-Graphy For Oligomers. II. Separation of Oligomers and Comparison With Conventional Columns

Abstract

Sixteen columns of 1.5 mm i.d. × 25 cm length packed with polystyrene gels of a particle diameter 10 ± 2 μm and having the exclusion limit of 8000 molecular weight as polystyrene were connected in series and used for the separation of oligomers such as oligostyrenes, epoxy resins, methylated melamine-formaldehyde resins, and phenol-formaldehyde resins of novolac and resol types. The observed overall value of the number of theoretical plates was 103000 plates/4 m. Separation results were compared with the conventional SEC which used two SEC columns of 8 mm i.d. × 30 cm length packed with PS gels of a particle diameter 6 ± 2 μm and having the same exclusion limit of the semimicro SEC. The value of N of this column was 17500 plates/30 cm. Oligostyrenes up to n = 11 (undecamer) were separated. Methyl ether derivatives of polynuclear methylol melamines up to penta-nuclear methylol melamine were separated. The possibility for separation of overlapping peaks by SEC having clearly higher efficiency was discussed.