Kinetic analysis of the transesterification of dimethyl terephthalate with ethylene glycol in a semibatch reactor

The kinetic analysis of the transesterification of ethylene glycol (EG) and dimethyl terephthalate (DMT) was studied in a semibatch reactor under nonisothermal conditions. The effect of the temperature profile, EG/DMT ratio, and catalyst concentration on the reaction rate was studied. Models were fitted by using an algorithm of parameter estimation in differential equations based on the Gauss–Newton method improved with the Marquardt extension. It was found that, unlike previous authors, the reaction rate was not a classical third order reaction of first order with respect to EG, DMT, and catalyst concentration, but the EG reaction order was 0.6 and a hyperbolic function was found to fit the relationship between reaction rate and catalyst concentration. Also, it was found that, at high conversions, the effect of the reverse reaction should not be neglected.     

荧光光谱法研究β-环糊精与齐墩果酸生成的包合物

在磷酸、硼酸及乙酸组成的缓冲介质中,齐墩果酸与β-环糊精反应生成包合络合物,其包合摩尔比为1比1。包合物的激发波长及发射波长的峰分别位于355nm及404nm处,在25℃条件下的结合常数为71L.mol-1,还测定了反应的热力学参数。测得ΔH0与ΔS0均大于0,说明此包合反应为吸热反应。测得ΔG0值小于0,且随反应温度升高而变得更负,说明此反应在试验条件下能自发进行,而随反应温度的升高,反应的自发性增强。     

Synthesis of N-arylated sultams: palladium- and copper-catalyzed cross coupling of aryl halides with 1,4-butane and 1,3-propanesultams

Palladium-catalyzed cross coupling of 1,4-butanesultam and 1,3-propanesultam with a variety of aryl halides was found to provide the desired products in 62-93% isolated yield using Xantphos as ligand. The Pd-catalyzed reaction was found to be superior to the analogous Cu-catalyzed reaction based on product yields, reaction rates, and substrate scope.     

The aza-Pudovik reaction accelerated in external constant magnetic field

The aza-Pudovik reaction of N-benzyl aromatic and aliphatic aldimines with dimethyl H-phosphonate was found to be accelerated significantly when carried out in an external magnetic field. Its conversion rates were analyzed and compared with those obtained during the aza-Pudovik reaction carried out under standard conditions. Magnetic acceleration was found to have a similar degree as in that observed in the Kabachnik–Fields reaction. However, the formation of the starting imines was found not to be susceptible to constant magnetic field–no acceleration was observed.     

Substituted γ-lactones. Some observations on the synthesis and reactivity of 4-aroyl-3-hydroxy-2(5H)-furanones

The reaction pathway towards formation of 4-aroyl-3-hydroxy-2(5H)-furanones 1 from the base catalyzed reaction between an acetophenone, diethyl oxalate and formaldehyde was investigated. If methoxide was used as base, a transesterification was found to occur in the first step, while a side reaction, namely the retro Claisen reaction, was in competition with the desired lactone formation in the second step. The nature of the solvent and the acidic character of 1 as well as the basicity of the aminoarylene were found to have a profound influence on the course of the reaction of 1 with aminoarylenes.     

Determination of Hydroxyl Groups in Epoxy Resins by Potentiometric Titration Using a Reaction with Maleic Anhydride

A reaction of maleic anhydride with epoxy–dian resins in methyl ethyl ketene was investigated. It was shown by potentiometric titration that the resulting maleic esters are stable to hydrolysis in acid and weakly acid organic solutions. This reaction can be used for the quantitative determination of hydroxyl groups in epoxy resins. Epoxy groups do not interfere with the formation of maleic esters under the conditions of determination. The optimal reaction conditions were found. The reaction kinetic was investigated, the reaction rate constants were determined at various temperatures, and the activation energy was found. The value of the activation energy indicates that the reaction is characterized by a low potential barrier.     

Mechanistic study of palladium catalyzed S-S and Se-Se bonds addition to alkynes

The mechanistic study of palladium catalyzed S-S and Se-Se bonds addition to alkynes revealed the involvement of dinuclear transition metal complexes in the catalytic cycle. Coordination of alkyne to dinuclear transition metal complex was found to be the rate determining step of the reaction. An unusual phosphine ligand effect increasing the yield of addition reaction was found in the studied system. A new synthetic procedure was developed to perform the catalytic reaction using easily available Pd(II) complex. The scope of the reaction and the reactivity of S-S and Se-Se bonds toward alkynes were investigated. The X-ray structure of the product of S-S bond addition reaction showed favorable geometry for the possible application as a chelate ligand.     

DFT studies on fructose and glycine maillard reaction: Formation of the heyns rearrangement products in the initial stage

DFT studies on the proposed mechanisms of the initial stage of Maillard reaction between ??-fructose (??-Fru)/??-fructose (??-Fru)/open chain fructose (O-Fru) and glycine (Gly) under different conditions revealed that ??-Fru was more reactive than ??-Fru and O-Fru, and O-Fru was less reactive than ??-Fru in the reaction. The reaction under basic conditions was found to be the most favorable for the formation of the Heyns rearrangement products (HRPs) in the initial stage, and the aqueous solution was found to be more feasible than the gaseous state reaction. The reaction under neutral conditions was the second most favorable for the production of HRPs. The reaction at the isoelectric point of glycine and under acidic conditions was found to be unfeasible to produce HRPs.     

Solid-Phase Functionauzation of Isotactic Polypropylene with Maleic Anhydride. Influence of Solvents and Additives on the Level of the Reaction

Abstract

Radical reaction between isotactic polypropylene and maleic anhydride initiated by peroxide at temperatures lower than the melting point of the polymer in the absence of liquid medium in the solid phase was studied. It was found that conversion of the reaction in the case of mixing of reagents into a pulverized polymer by the impregnation method is satisfactory in comparison with reaction conversion in the melt. It was found that reaction conversion in the solid phase can be increased up to 30% in the presence of a small amount of an organic solution, such as xylene (5 to 10%).     

The Diels-Alder reaction of C60 and cyclopentadiene in mesoporous silica as a reaction medium

As a new organic reaction medium, a periodic mesoporous inorganic material was found to function as a "solid solvent" in a Diels-Alder reaction of C(60) with cyclopentadiene. This finding was supported by a concentration effect and a kinetic study of the reaction.     

The Effect of the Equatorial Environment on Oxo‐Group Silylation of the Uranyl Dication: A Computational Study

A theoretical investigation of the reductive oxo‐group silylation reaction of the uranyl dication held in a Pacman macrocylic environment has been carried out. The effect of the modeling of the Pacman ligand on the reaction profiles is found to be important, with the dipotassiation of a single oxo group identified as a key component in promoting the reaction between the Si? X and uranium–oxo bonds. This reductive silylation reaction is also proposed to occur in an aqueous environment but was found not to operate on bare ions; in this latter case, substitution of a ligand in the equatorial plane was the most likely reaction. These results demonstrate the importance of the presence but not the identity of the equatorial ligands upon the silylation of the uranyl U? O bond.     

细胞色素C在聚乙烯氧化物修饰的金电极上的直接电化学反应

本文报道了细胞色素Ｃ在聚乙烯氧化物修饰的金电极上的直接电化学行为，发现ＰＥＯ是细胞色素Ｃ电化学反应的促进剂，ＰＥＯ修饰膜的形态对细胞色素Ｃ电化学反应的可逆性有较大的影响。     

An extremely efficient three-component reaction of aldehydes/ketones, amines, and phosphites (Kabachnik-Fields reaction) for the synthesis of alpha-aminophosphonates catalyzed by magnesium perchlorate

Commercially available magnesium perchlorate is reported as an extremely efficient catalyst for the synthesis of alpha-aminophosphonates. A three-component reaction (3-CR) of an amine, an aldehyde or a ketone, and a di-/trialkyl phosphite (Kabachnik-Fields reaction) took place in one pot under solvent-free conditions to afford the corresponding alpha-aminophosphonates in high yields and short times. The use of solvent retards the rate of the reaction and requires a much longer reaction time than that for neat conditions. The reactions involving an aldehyde, an aromatic amine without any electron-withdrawing substituent, and a phosphite are carried out at rt. The reactions involving cyclic ketones, aromatic amines with an electron-withdrawing substituent, and aryl alkyl ketone (e.g., acetophenone) require longer reaction times at rt or heating. Magnesium perchlorate was found to be superior to other metal perchlorates and metal triflates during the reaction of 4-methoxybenzaldehyde, 2,4-dinitroaniline, and dimethyl phosphite. The catalytic activity of various magnesium compounds was influenced by the counteranion, and magnesium perchlorate was found to be the most effective. The reaction was found to be general with di-/trialkyl phosphites and diaryl phosphite. The Mg(ClO4)2-catalyzed alpha-aminophosphonate synthesis in the present study perhaps represents a true three-component reaction as no intermediate formation of either an imine or alpha-hydroxy phosphonate was observed that indicated the simultaneous involvement of the carbonyl compound, the amine, and the phosphite in the transition state.     

The reactivity in the system CuCl-Si related to the activation of silicon in the Direct Synthesis

The reaction between cuprous chloride CuCl and silicon is the classical model reaction for activation of the contact mass in Direct Synthesis. It had been found by several authors that the reactivity of CuCl strongly depends on its quality and the route of synthesis. In the present study the reactivities of two CuCl charges, prepared from the elements at high temperatures and by reduction in aqueous solution, are compared by means of calorimetric studies. The aqueous route CuCl was found to have a higher reactivity, indicated by lower reaction start temperatures and 100% CuCl conversion with respect to the other charge. It was found that the reactivity depends neither on intrinsic properties (defect concentration) nor on properties that can be derived from microscopical or thermoanalytical characterizations or by X-ray powder diffraction. The initial step of reaction between cuprous chloride and silicon was identified as a solid state reaction. Therefore, the role of the CuCl surface is discussed and a model for the initial step is suggested.     

Ultrasound‐Assisted Pechmann Condensation of Phenols With β‐Ketoesters to Form Coumarins,in the Presence of Bismuth(III) Chloride Catalyst

Ultrasound was found to synergistically accelerate the condensation of phenol with β‐ketoesters in the presence of BiCl₃. In the absence of ultrasound, under the same conditions, the reaction was found to be slow. Thus, the reaction can be carried out in the presence of ultrasound at room temperature (28–30°C), with a considerable reduction of reaction time, with high yield and high purity of coumarins.     

Orientation dependence for Br formation in the reaction of oriented OH radical with HBr molecule

The orientation dependence of Br-atom formation in the reaction of the oriented OH radical with the HBr molecule using the hexapole electrostatic field was studied. Experimental results for the orientation dependence in the reaction were analyzed using a Legendre polynomial fit. The results show two reactive sites. It was found that O-end attack is most favored for this reaction, and that H-end attack also shows a pronounced reactivity. The reactivity of the side-ways attack was found to be small. By comparing the results of the orientation dependence in the reaction with studies of inelastic collisions and theoretical calculations, two reaction pathways are proposed. Reaction by O-end attack is followed by a direct abstraction of the H-atom from the HBr molecule. The mechanism for H-end attack may have H-atom migration from HBr to form the water molecule.     

N-Tosylaziridine, a new substrate for chemical fixation of carbon dioxide via ring expansion reaction under atmospheric pressure

N-Tosylaziridine was found to be a useful substrate for cycloaddition reaction with carbon dioxide. The reaction was successfully catalyzed by lithium bromide under atmospheric pressure to give the corresponding five-membered cyclic urethane, N-tosyl-1,3-oxazolidin-2-one, selectively. It was found that electron-donating nature of the substituent at 2-position of N-tosylaziridine accelerated the reaction, and this tendency allowed us to estimate the reaction mechanism.     

The Kinetic Aspects of the Interaction of Nitrite Ions with Sulfanilic Acid and 1-Naphthylamine in Aqueous and Micellar Media

The kinetics of the reaction of nitrite ions with sulfanilic acid and 1-naphthylamine in aqueous and micellar (sodium dodecyl sulfate) media was studied step-by-step. The diazotization of sulfanilic acid with the nitrite ion was found to occur virtually instantaneously. Anionic surfactant micelles did not influence the rate of this reaction. The calculated effective rate constants and activation energies of the azo coupling reaction between synthesized sulfophenyldiazonium and 1-naphthylamine showed that the passage from water into the micellar medium decelerated the reaction. It was found that sodium dodecyl sulfate micelles played the role of a reagent separator.     

Synthesis of functionalized m-bistrifluoromethylbenzenes via cyclocondensation of 1,1,1,5,5,5-hexafluoroacetylacetone with enamines

The reaction of 1,1,1,5,5,5-hexafluoroacetylacetone with push-pull enamines having a methyl group at the α-position was investigated. It was found that the reaction is sensitive both to the structure of enamines and to reaction conditions. As a result, a set of bistrifluoromethyldialkylanilines and ethyl bistrifluoromethylsalicylate was prepared. Plausible mechanisms and factors influencing the course of the reaction are discussed.