New Mechanistic Aspects of the Fenton Reaction

The kinetics of the Fenton reaction was studied in detail. A second reaction step in the presence of excess H₂O₂ is attributed to formation of the complex Fe^III(^?O₂H)_aq. Therefore, the reaction of Fe(H₂O)₆²⁺ with Fe^III(^?O₂H)_aq in the presence of Fe^II to form Fe^III_aq (k=(7.7±1.5)×10⁵ M ^?1 s^?1) may contribute to the overall Fenton reaction, and could account for some of the debate in the literature concerning its detailed mechanism. If this is correct for LFe^III(^?O₂H)_aq also, then it might be of significant biological importance. The activation parameters ΔH^≠, ΔS^≠, and ΔV^≠ for the Fenton reaction were measured under various experimental conditions, and are used in the mechanistic interpretation.     

New Aspects of the Reaction of Thioacetamide and N-Substituted Maleimides

N-Arylmaleimides are universal substrates for the synthesis of various heterocyclic compounds with a wide spectrum of biological activity. However, their reactions with thioacetamides have not been comprehensively studied. We studied the reactions of thioacetamide with N-arylmaleimides under various conditions. We established for the first time that three types of products: epithiopyrrolo[3,4-c]pyridines, pyrrolo[3,4-c]pyridines and 3,3′-thiobis(1-arylpyrrolidine-2,5-diones) can be obtained in different conditions. In all cases, two maleimide molecules are involved in the reaction. 3,3′-Thiobis(1-arylpyrrolidine-2,5-diones) are the major products when the reaction is conducted at boiling in acetic acid. When thioacetamide and N-arylmaleimide are kept in dioxane at 50 °C, epithiopyrrolo[3,4-c]pyridines can be isolated, which, when heated in dioxane, in acetic acid or in methanol in the presence of catalytic amounts of sodium methoxide, are converted into pyrrolo[3,4-c]pyridines by eliminating hydrogen sulfide. The reaction of thioacetamide and N-arylmaleimide in dioxane at boiling temperature with the portioned addition of N-arylmaleimide leads predominantly to the formation of pyrrolo[3,4-c]pyridines. The reaction of thioacetamide with N-alkylmaleimides under all the above conditions leads predominantly to the formation of the corresponding sulfides. The structure of the compounds obtained was characterized by a set of spectral analysis methods and X-ray diffraction (XRD) data.     

Some Aspects of the Reaction of Polyacrylamide with Formaldehyde

The reaction of polyacrylamide with formaldehyde was studied in a neutral aqueous medium at equal initial molar concentrations of amide groups and of formaldehyde (0.05 mol/L) and in a range of temperatures from 45 to 75°C. The process was investigated by measuring the loss of free formaldehyde in the reaction mixture and the changes of the sum of free formaldehyde and methylol groups versus time. The addition of HCHO to an amide function of the polymer leads to its N-methylol derivative which may transform into the product of condensation between the latter and another amide group. Because of high dilution of polyacrylamide macromolecules in the reaction mixtures studied, cross-linking of the polymer chains with formaldehyde is rather unlikely. Therefore the disappearance of the N-methylols formed is probably due to some intramolecular reactions. It is believed that they involve the condensation of N-hydroxymethyls with neighboring amide groups which results in cyclic structures containing methylenediamide sequences. The occurrence of intramolecular reactions was confirmed by applying Flory's theory of gelation. The addition of HCHO to amide functions is a rate-determining stage in the case of polyacrylamide. For this reaction the rate constants were estimated and the corresponding activation energy was found to be 62 kJ/mol.     

New Aspects of the Maillard Reaction in Foods and in the Human Body

The reactions that occur during the cooking, baking, and preservation of foods of all kinds are of great importance for the production of aroma, taste, and color. However, more recently it has been shown that these reactions may be accompanied by a reduction in nutritive value and the formation of toxic compounds. For these reasons, the very complex reactions between reducing sugars and the free amino groups of amino acids or proteins, known as non-enzymatic browning or the Maillard reaction, have again caught the interest of chemists. The Maillard reaction came to be seen in a new light as it was realized that it actually occurred in the human body. As a general rule, the longer the half-life of a protein, the larger the amount of its Maillard products found, i.e., important factors are the ‘age’ or persistence of the protein in the body and the glucose concentration, particularly in diabetics. Many of the symptoms developed by diabetics resemble those of premature aging, which leads to the possibility that glucose, because of its reactivity towards proteins, is fundamentally involved in the normally slow progress of aging.     

F原子与臭氧反应机理的量子化学研究

用量子化学从头计算UMP2方法，在UPM2/6 311＋G水平上，研究F 原子与臭氧反应机理，优化了反应物、产物、中间体和过渡态的几何构型，在UQCISD（T）/6 311＋G水平上计算能量，同时进行零点能校正.研究结果表明， F原子与臭氧之间有很强的反应活性.     

Novel Synthetic Aspects of the Staudinger Reaction

Abstract

New applications of the Staudinger reaction for the preparation of amines are discussed.     

Structural Aspects of Fluorosilicic Acid Reaction with Organic Bases

The results of systematic studies into the structures of products formed in reactions between fluorosilicic acid (FSA) and organic bases are presented. Different hydrolytically labile silicon fluoride complexes contained in these products are stabilized. A debatable problem of FSA state in aqueous solutions is discussed in the light of the data obtained.     

Reactions of Aliphatic Diazo Compounds: V. Reaction of Methyl Diazoacetate with Imides of Itaconic Acid

Methyl diazoacetate regioselectively adds to N-substituted imides of itaconic acid to afford 2-pyrazolines, methyl 7-aryl-6,8-dioxo-1,2,7-triazaspiro[4.4]non-2-ene-3-carboxylates that in reaction with halogens (Cl₂, Br₂) yield methyl 5-aryl-1-halo-4,6-dioxo-5-azaspiro[2.4]heptane-1-carboxylates as a mixture of syn- and anti-isomers.     

氟原子与反式1,3-丁二烯分子反应动力学的理论研究

Theoretical studies of F atom reaction with trans-1,3-butadiene were carried out at the CCSD(T)/6-311G(d,p)/B3LYP/6-311G(d,p) levels. Energies and structures for all reactants, products and transition states were determined. Two reaction pathways involving the formation of the complexes CH2CHCHFCH2 and CH2CHCHCH2F were found in this reaction. Theoretical results suggest that the H atom channel observed in previous crossed beam experiment occurs likely via these two long-lived complex formation pathways. For the complex CH2CHCHFCH2 pathway, another reaction channel (C2H3+C2H3F) is also accessible. Relative importance of the C2H3+C2H3F channel versus the H formation channel via the same reaction pathway has also been estimated, suggesting that it would be difficult to observe the C2H3+C2H3F channel in a crossed molecular beam experiment. Theoretical analysis also shows that the HF formation proceeds via direct abstraction mechanisms, though it is likely a minor process in this reaction.     

Mechanistic Aspects of the Palladium-Catalyzed Suzuki-Miyaura Cross-Coupling Reaction

The story of C−C bond formation includes several reactions, and surely Suzuki-Miyaura is among the most outstanding ones. Herein, a brief historical overview of insights regarding the reaction mechanism is provided. In particular, the formation of the catalytically active species is probably the main concern, thus the preactivation is in competition with, or even assumes the role of the rate determining step (rds) of the overall reaction. Computational chemistry is key in identifying the rds and thus leading to milder conditions on an experimental level by means of predictive catalysis.     

New Salt Spiropyran of Indoline Series with Fluorine Substituent

Synthesis, study of structure and photochromic properties of new salt spiropyran of indoline series containing a fluorine substituent in the 6′-position of the 2H-chromene moiety have been described in the work. The structure of the compound has been confirmed by ¹H NMR spectroscopy and X-ray diffraction analysis. Comparison of the structure of the compound with the previously studied analogue containing a methyl group instead of a fluorine atom in the 6′-position of the [2H]-chromene moiety has been made. This compound has been found to be photochromic, long-wavelength absorption maximum of its open form shows a bathochromic shift, and lifetime is increased three times as compared with the methyl analogue.     

AIM Study on the Reaction of CH2SH Radical with Fluorine Atom

The reaction of CH2SH radical with fluorine atom was studied at the levels of B3LYP/6-311G(d,p) and MP2(Full)/6-311G(d,p). The computational results show that the reaction has three channels and proceeds by the addition of fluorine atoms on carbon or sulfur sites of CH2SH, forming initial intermediates. The calculated results show that the channel in which fluorine attaches to the carbon atom to form CH2S and HF, is the most likely reaction pathway. Topological analysis of electron density was carried out for the three channels. The change trends of the chemical bonds on the reaction paths were discussed. The energy transition states and the structure transition regions (states) of the three channels were found. The calculated results show that the structure transition regions are broad in unobvious exothermic reactions or unobvious endothermic reactions, and are narrow in obvious exothermic reactions or obvious endothermic reactions.     

N-Cyanoimides via the Cyanation of Imides

The conversion of cyclic imides to the corresponding N-cyanoimides has been carried out using cyanogen bromide as the nitrile source. This methodology provides a convenient route for the preparation of both aromatic and aliphatic N-cyanoimides.     

Reactions of Aliphatic Diazo Compounds: IV. Reaction of Diphenyldiazomethane with Substituted Imides of Maleic and Itaconic Acids

Diphenyldiazomethane regioselectively adds to 2-R-substituted maleimides to yield 1-pyrazoline derivatives, 1-R-7-aryl-6,8-dioxo-4,4-diphenyl-2,3,7-triazabicyclo[3.3.0]oct-2-enes that on heating liberate nitrogen to afford substituted 3-azabicyclo[3.1.0]hexanes. To the N-arylsubstituted imides of itaconic acid the diphenyldiazomethane adds to furnish 5-aryl-4,6-dioxo-1,1-diphenyl-5-azaspiro[2.4]heptanes.     

Some Aspects of the Reaction between Chitosan and Formaldehyde

Reactions of chitosan (degree of deacetylation 67%, weight-average molecular weight 850,000) with formaldehyde were performed in a dilute aqueous acetic acid solution at a molar ratio of amino groups of the polymer to HCHO of 0.06:O.1 mol/L and at different temperatures (45, 60, and 75°C). In each case the pH of the reaction mixtures was 3.4 during the experiments. The process was investigated by measuring the kinetic changes of the free formaldehyde concentration and the sum of free formaldehyde and methylol groups produced. No gelation of the reaction product was observed. The experimental results led to the conclusion that the methylol groups formed by the addition of HCHO to chitosan functions take part in some intramolecular reactions with amino and/or hydroxyl groups of chitosan. Initially, the concentration of the resultant methylene bridges grows rapidly and then drops again until an equilibrium is established. This rather unusual decomposition of the methylene links once formed without changing the reaction conditions is accompanied by a substantial growth of the amount of methylol derivative whose concentration at the beginning of the process increased rather slowly.     

Some Aspects of the Azide-Alkyne 1,3-Dipolar Cycloaddition Reaction

Russian Journal of Organic Chemistry - Some peculiar features of two most commonly used catalytic systems (Cul and CuSOVsodium ascorbate) controlling the regioselectivity of 1,3-dipolar...