Study of kinetics of thermal degradation and to determine the activation energies of polyamides based on s-triazine

A series of ten polyamides was prepared by the high-temperature polycondensation of 4,6-bis(N-(4-(benzoylchloride)amino))-2-(N-phenyl- piperazin-1-yl)-1,3,5-triazine with different aromatic and aliphatic diamines. The synthesized polyamides were analyzed by physico-chemical properties such as solubility, density, viscosity etc. The structure of prepared polyamides was evaluated by ¹H NMR and FTIR spectrum. Thermogravimetric analysis used to study the kinetics of thermal degradation of some synthesized polyamides. Broido, Horowitz & Metzger, Coats Redfern and Chan et al. models were applied to respective thermograms to determine the activation energy (E_a). Activation energy data shows that the polyamides obtained from aromatic diamine has greater stability than the polyamides obtained from aliphatic amine.     

Oxidation of benzylic methylenes to ketones with Oxone-KBr in aqueous acetonitrile under transition metal free conditions

A green and highly efficient protocol for the oxidation of benzylic methylenes to their corresponding ketones with a combination of Oxone and KBr in aqueous acetonitrile is developed. The H₂¹⁸O labeling experiment demonstrated that the oxygen introduced into ketone originated from water. A plausible mechanism was also suggested.     

Thermal Oxidation and Its Relation to Chemiluminescence from Polyolefins and Polyamides

Chemiluminescence (CL) from oxidation of polypropylene, polyethylene and polyamide has been compared and kinetic parameters based on the simplified kinetic scheme involving both bimolecular decomposition of hydroperoxides as an initiating event and correction for the oxidation spreading were determined. Induction times of oxidation determined from the autocatalytic shape of chemiluminescence intensity-time runs increase with an increasing initial molar mass of polypropylene within low molar masses up to 180 kDa regardless of the route of the polypropylene synthesis. The more complex chemiluminescence patterns in case of polyamides may be related with an increase of initially present defect structures including the terminal amino groups.     

Study of oxidation properties and decomposition kinetics of three-dimensional (3-D) braided carbon fiber

The XRD, SEM, isothermal oxidation-weight loss and non-isothermal thermogravimetry (TG)-differential thermogravimetry (DTG) were used to study the oxidation properties and oxidation decomposition kinetics of three-dimensional (3-D) braided carbon fiber (abbreviated as fiber). The results showed that the non-isothermal oxidation process of fiber exhibited self-catalytic characteristic. The kinetic parameters and oxidation mechanism of fiber were studied through analyzing the TG and DTG data by differential and integral methods. The oxidation mechanism was random nucleation, the kinetic parameters were: lg A=10.299 min⁻¹; E_a=156.29 kJ mol⁻¹.     

金属氧化动力学规律和耐热钢中稀土作用的研究

根据气固相反应动力学理论推导出金属氧化不同阶段和不同几何２样品的动力学方程，实验研究了耐热钢３Ｃｒ２４Ｎｉ７Ｎ高温氧化中稀土的作用实验结果表明，稀土未改变耐热钢的氧化动力学机理，理论推导的氧化动力学方程可以很好地描述实际金属氧化的动力学规律。     

Oxidation of aniline and some para-substituted anilines by benzimidazolium fluorochromate in aqueous acetic acid medium – A kinetic and mechanistic study

The oxidation kinetics of some para-substituted anilines by benzimidazolium fluorochromate (BIFC) have been studied in aqueous acetic acid media in the presence of perchloric acid. The reaction is first order with respect to both aniline and BIFC and is catalysed by a hydrogen ion. The rate data obey Hammett relationship. The products of oxidation are the corresponding azo benzenes. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of BIFC with anilines.     

Application de la diphényl-acroléine à l'analyse fonctionnelle

In highly acid alcoholic medium, diphenyl-acrolein develops a red colour with m-diphenols, in the cold. This reaction, which makes it possible to carry out determinations, has a sensitivity of one μg. Under the same conditions, yellow colouring is obtained with methylenes in the α position of a carboxyl or with primary aromatic amino groups. Various condensation products have been isolated.     

肾上腺素氧化反应的研究——生成肾上腺素红及其进一步氧化反应的研究

利用紫外吸收光谱法结合计算机模拟研究了肾上腺素(Adin)在Cu(Ⅱ)离子催化下,用H₂O₂氧化产生肾上腺素红(Adorn)及其进一步反应的动力学。考察了有关反应的速率随Adin的初始浓度、Cu(Ⅱ)高子浓度和H₂O₂浓度的变化情况。并提出有关反应可能的机理,半定量地解释了相应的动力学行为。     

Kinetics and mechanism of permanganate oxidation of pectin polysaccharide in acid perchlorate media

The kinetics of oxidation of pectin polysaccharide as a natural polymer by permanganate ion in aqueous perchloric acid at a constant ionic strength of 2.0 mol dm⁻³ has been investigated spectrophotometrically. The reaction time curves showed two distinct stages, the initial stage was relatively slow, followed by an increase in the rate of oxidation at longer times. The results of the initial rates reveal first-order kinetics in permanganate ion and fractional-order with respect to pectin concentration. Kinetic evidence for the formation of an intermediate complex between the polysaccharide and the oxidant is presented. The results obtained at various hydrogen ion concentrations showed that the reaction is acid catalyzed. The added salts lead to the prediction that Mn⁴⁺ and/or Mn³⁺ play an important role in the autoaccleration period kinetics. A tentative reaction mechanism consistent with the kinetic results is discussed.     

Parallel synthesis of H-pin polyamides by alkene metathesis on solid phase

A small library of H-pin polyamides with variable aliphatic bridge lengths (CH(2))(n)(), where n = 4-8, connecting a central Py/Py pair was prepared via parallel synthesis with Ru-catalyzed alkene metathesis on solid phase as a complexity-generating cross-linking reaction. DNA binding affinities and sequence specificities were analyzed for each member of the library to determine the optimum linker length. An H-pin polyamide with a six-methylene bridge was found to have the highest affinity to its match site with high selectivity over a 1-bp mismatch site. The relationship between the number of methylenes in the linker (CH(2))(n)() and affinity is n = 6 > 4 > 7 > 5 > 8. These results indicate that 6 followed by 4 methylene-bridged polyamides represent the optimum spacer length for the H-pin motif in the DNA minor groove. Importantly, the H-pin is competitive with hairpin polyamides with respect to affinity and specificity. The metathesis-based convergent synthetic route to H-pin polyamides expands the scope of readily available DNA recognition motifs for small molecule-based gene regulation studies.     

Kinetics of Oxidation of 4-Oxoacids by <Emphasis Type="Italic">N</Emphasis>-Chlorosaccharin in Aqueous Acetic Acid Medium

The oxidation kinetics of substituted and unsubstituted 4-oxoacids (S) by N-chlorosaccharin (NCSA) have been studied in aqueous acetic acid media. The reaction follows first-order kinetics in each of the 4-oxoacids, NCSA and H⁺. The effect of changes in the electronic nature of the substrate reveals that positive charge develops in the transition state. Based on the kinetic results and product analysis, a suitable mechanism has been proposed for the reaction of NCSA with 4-oxoacids.     

Pt/HM、Pd/HM催化剂上CO氧化反应活性和动力学研究

研究了Pt/HM、Pd/HM催化剂上CO氧化反应的活性,求出了各种催化剂的CO氧化反应动力学方程。考察了不同气氛下CO氧化活性的演变规律和V⁴⁺、Co²⁺离子对Pt、Pd的助催化作用,并用催化剂集团结构适应模型对以上结果作出了解释。     

Oxidative Kinetic Resolution of Cyclic Benzylic Ethers

A manganese‐catalyzed oxidative kinetic resolution of cyclic benzylic ethers through asymmetric C(sp³)?H oxidation is reported. The practical approach is applicable to a wide range of 1,3‐dihydroisobenzofurans bearing diverse functional groups and substituent patterns at the α position with extremely efficient enantiodiscrimination. The generality of the strategy was further demonstrated by efficient oxidative kinetic resolution of another type of five‐membered cyclic benzylic ether, 2,3‐dihydrobenzofurans, and six‐membered 6H‐benzo[c]chromenes. Direct late‐stage oxidative kinetic resolution of bioactive molecules that are otherwise difficult to access was further explored.     

Thermokinetic study of the oxidation of ZrAl3 powders

The oxidation kinetics of ball milled ZrAl₃ powder was investigated by thermogravimetry at temperatures up to 1100 ° C. The non-selective oxidation of ZrAl₃ results in the formation of -Al₂ O₃, tetragonal and monoclinic ZrO₂. Non-isothermal and isothermal measurements were simultaneously used in a multivariate non-linear regression analysis to determine the kinetic reaction parameters. The oxidation process is well described by a generalized n-dimensional Avrami type rate equation, according to a diffusion limited growth reaction with an apparent activation energy of 244 kJ/mol. Significant improvement of the fit quality of the kinetic data is achieved through a two-step kinetic model indicating a complex oxidation mechanism.     

Synthesis and Characterization of Novel Biodegradable Polyamides Containing α-amino Acid

The polyamides were obtained from 1,6-hexanediamine and diacylchloride which incorporated α -amino acid residues through interfacial polycondensation. High molecular weight (η_inh = 1.05–1.18 dL/g) polymers were produced with high yields. The structure of polyamides was verified by FT-IR and ¹H NMR spectra. They showed a remarkable ability to develop high crystallinity with melting temperatures in the range 117–191°C and was stable up to 350°C under nitrogen. Two methods such as alkali hydrolysis (10% NaOH w/v, 80°C) and enzymatic hydrolysis were employed for assessing the susceptibility of these polyamides to degradation. A preliminary investigation of the 5-fluorouracil (5-FU) release characteristics of these polyamides showed that the release rate increased with increasing water absorption of the polymers.     

Study of the factors affecting the photoelectrode characteristics of a perylene/phthalocyanine bilayer working in the water phase

Some types of phthalocyanines (MPc (M = H(2), Cu, or Zn), a p-type semiconductor) were used in combination with 3,4,9,10-perylenetetracarboxyl-bisbenzimidazole (PTCBI, an n-type semiconductor), with which those photoelectrode characteristics in the water phase were investigated in terms of kinetics. Each film of the PTCBI/MPc bilayer functioned as a photoanode, where the photoinduced oxidation of thiol occurs at the MPc/water interface along with the hole conduction through the MPc layer. The holes originate on account of the photophysical events in the p/n interior, involving the charge separation of excitons at the p/n interface. The typical photoelectrochemical characteristic in the PTCBI/MPc photoanodes involved a transient photocurrent occurring in the initial stage under illumination (under potentiostatic conditions): thereafter, it attained a steady state. Moreover, both the initial spiky photocurrents and the steady-state photocurrents exhibited saturation at higher concentrations. An analysis with photoelectrode kinetics was performed by assuming an adsorption step prior to a rate-limiting charge transfer step, where equations were applied to photocurrents based on the Langmuir adsorption equilibrium. The kinetic analyses evidently showed that the photoanodic reactions are kinetically dominated by the charge transfer between MPc and thiol, where the overall kinetics for thiol oxidation decreases in the following order: H(2)Pc > ZnPc > CuPc; that is, it appeared that H(2)Pc acts as the more efficient photofunctional interface capable of oxidation in the water phase when PTCBI was concurrently employed as an electron conductor. Considering that the photocurrent generated is proportional to the surface concentration of thiol (Gamma) at the MPc as well as the intrinsic oxidation rate (cf., ZnPc > H(2)Pc approximately CuPc), the higher efficiency in the output at the H(2)Pc surface was attributed to an exceptionally high Gamma (i.e., from the kinetic analyses, the Gamma value at the H(2)Pc surface was also inferred to be 2-3 times higher than that at the other MPcs). Through the present kinetic analysis, it also revealed that the activity for thiol oxidation taking place at Pc ring is comparable to that at the conventional active catalysts (i.e., polycarboxyphthalocyaninato Co(ii) and Fe(iii)) where a central metal is an active site.     

Electrochemical studies of the oxidation mechanism of polyamide on glassy carbon electrode

Polyamides containing N-methyl pyrroles and N-methyl imidazoles are a type of small molecule that can bind and recognize the bases of DNA with high affinity and specificity. Five polyamides were studied at glassy carbon electrode in acetate buffer by cyclic and differential pulse voltammetry to clarify their redox pathways. The polyamide electrochemical responses are compared by peak currents and peak potentials. The slopes of the three anodic E_p vs. pH plots of a typical polyamide are linear and show 0.059, 0.057, 0.056 V per pH in acid media, respectively, which correspond to a mechanism involving the equal number of electrons and protons. A possible mechanism for the redox pathway of various polyamides is proposed: the oxidation product of imidazole ring is acylamide and the results of in situ UV–Vis spectroscopy at Pt web electrode support the proposed mechanism. electrospray ionization mass spectroscopy (ESI-MS) indicates that one or two oxygen atoms are added into polyamide molecule after electrochemical oxidation.     

Peroxidation of caprolactam and its effect on equilibrium polymerization

The peroxidation of caprolactam has been studied at 84°C, 100°C and 120°C. The decomposition of the initially formed ε-caprolactam hydroperoxide was found to be catalyzed by adipic acid monoamide which is formed by hydrolysis of adipimide. This imide results from the decomposition of the hydroperoxide and was found to act as oxidation inhibitor. The molecular weights of the polyamides obtained by polymerizing the peroxidized caprolactam were found to decrease as the extent of peroxidation and thus the concentration of adipic acid monoamide and other decomposition products increased. In all of these polyamides the concentration of acidic functions was appreciably higher than that of the titratable amino endgroups.     

Thermolysis of polyethylene hydroperoxides in the melt, Part 12: Mechanisms and kinetics of thermolysis

The thermolysis of polyethylene hydroperoxides is attributed to the reaction of two hydroperoxide groups. This bimolecular reaction appears as a first-order reaction with the mean values of the hydroperoxide concentrations that can be used for the experimental verification of the kinetics. In low molecular mass liquids and solutions these findings would be irreconcilable. However, in polymer melts, this contradiction is more apparent than real. It is a consequence of the heterogeneous kinetics valid in polymer melts. The bimolecular reaction involves the decomposition of pairs of hydroperoxide groups that are relatively close in the elementary oxidation volumes. By diffusion these hydroperoxide groups can come close enough for reaction. From the chemical point of view the decomposition is a bimolecular reaction. However, from the kinetic point of view it is a first-order reaction of the hydroperoxide pairs. The dependency of the first-order rate on the initial hydroperoxide concentration is explained by the heterogeneous kinetics. The activation energy of the overall process can be related to the sum of the activation energies pertaining to the chemical reaction and to the diffusion process.     

Kinetics of the thorough oxidation of traces of saturated hydrocarbons in air

Conclusions The kinetics of the thorough oxidation on a platinum-aluminum catalyst of small quantities of n-pentane, h-heptane, and n-nonane has been investigated. Under comparable conditions n-pentane is oxidized considerably more slowly than n-heptane and n-nonane. A kinetic equation has been found which describes the reaction rate in all the systems studied.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1728–1734, August, 1981.