Kinetics and mechanism of the reaction of dimethyldioxirane with cumene

The reaction of dimethyldioxirane with cumene (22–52°C) follows a chain-radical mechanism. The kinetic regularities of this reaction were studied by the chemiluminescence and kinetic UV spectrophotometry methods by monitoring the consumption of dioxirane. The process is inhibited by oxygen. In the absence of O₂, the process is accelerated due to the decomposition of dimethyldioxirane induced by alkyl radicals. In this case, the reaction occurs according to a complicated kinetic law including the first and second orders with respect to dioxirane. Based on the kinetics and reaction products, the scheme of the process was proposed. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 694–702, April, 1997.     

Kinetic study of oxidation of N‐(α‐methylbenzylidene) anilines by dimethyldioxirane

A kinetic study of the oxidation of substituted N‐(α‐methylbenzylidene) anilines by dimethyldioxirane was investigated using a UV/VIS spectrophotometer. Oxaziridines and nitrones were formed as intermediates, and in the excess of dimethyldioxirane corresponding carbonyl compounds, nitrosobenzene or nitrobenzene, were formed quantitatively. The kinetic data were used in the equation for the formation of oxaziridines and nitrones as an intermediate and further oxidation to the corresponding acetophenones and nitrosobenzene. Hammett ρ values were determined for compounds p‐substituted on the aromatic ring attached to the carbon atom of the imino group, and it was found that these substituents have very little effect on the oxidation reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 492–497, 2007     

Kinetics of the reaction between dimethyldioxirane and 2-methylbutane

The kinetics of the reaction between dimethyldioxirane and 2-methylbutane in acetone solutions were studied spectrophotometrically at 25 °C. The radical-chain induced decomposition of dioxirane proceeding with the participation of the carbon-centered radicals follows the first-order kinetic law. The reaction is inhibited by dioxygen. In the presence of O₂, the dimethyldioxirane consumption is due to the homolysis of the O−O bond (at a rate constant of 6.3·10⁻⁴ s⁻¹) followed by attack of the C−H bond of 2-methylbutane by the biradical formed. The rate constant of the reaction between the alkyl radical and dimethyldioxirane was estimated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1785–1788, October, 1997.     

Coumarins with an unprecedented tetracyclic skeleton and coumarin dimers from chemically engineered extracts of a marine-derived fungus

The unprecedented tetracyclic coumarin derivatives 1 and 2 and the coumarin dimers 3–5 were isolated from chemically engineered extracts (coumarin dimerization of natural extract) of the marine-derived fungus Eurotium rubrum. The structures of these compounds were established using NMR, MS and IR methods. The absolute configuration of 1 was determined by ECD calculations. The unprecedented tetracyclic coumarin skeleton was generated by domino-Knoevenagel-Diels-Alder reactions. Compounds 1–5 showed tyrosinase inhibitory activity (IC₅₀?=?1.7, 1.2, 4.9, 1.8 and 2.9?μM, respectively). The isolated coumarin derivatives 1–5 were not observed by HPLC analysis in crude extracts of E. rubrum, suggesting that chemically engineered extract generated these new coumarin derivatives with tyrosinase inhibitory activity.     

Oxidative transformations of 4‐methylcoumarins using dimethyldioxirane

Efficient regioselective oxidation of the double C? C bond of 4‐methylcoumarins with isolated dimethyldioxirane was performed, and related hydroxy and epoxy derivatives were obtained in good yields. All of obtained epoxides and most of hydroxy derivatives are novel compounds. The position of different electron‐donating groups attached at the aromatic part of molecule shows significant influence on kinetics and course of the reaction. J. Heterocyclic Chem., (2011).     

A comparative LSER study of the reactivity of 2‐substituted cyclohex‐1‐eneacetic and 2‐substituted phenylacetic acids with diazodiphenylmethane in various solvents

The rate constants for the reaction of 2‐substituted cyclohex‐1‐eneacetic and 2‐substituted phenylacetic acids with diazodiphenylmethane were determined in various aprotic solvents at 30°C. To explain the kinetic results through solvent effects, the second‐order rate constants of the examined acids were correlated using the Kamlet–Taft solvatochromic equation. The correlations of the kinetic data were carried out by means of multiple linear regression analysis, and the solvent effects on the reaction rates were analyzed in terms of initial and transition state contributions. The opposite signs of the electrophilic and the nucleophilic parameters are in agreement with the well‐known mechanism of the reaction of carboxylic acids with diazodiphenylmethane. The quantitative relationship between the molecular structure and the chemical reactivity is discussed, as well as the effect of the molecular geometry on the reactivity of the examined compounds. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 613–622, 2009     

Hydrogenation of coumarin to octahydrocoumarin over a Ru/C catalyst

The production of octahydrocoumarin, which can serve as a replacement for toxic coumarin, was investigated using 5% Ru on active carbon (Ru/C) as the catalyst for the hydrogenation of couma-rin. The hydrogenation was studied by optimizing the reaction conditions (pressure, solvent and coumarin concentration). The activity and selectivity of the Ru/C catalyst were compared for dif-ferent solvents. The mechanism of coumarin hydrogenation was deduced. The formation of side products was explained. The optimal hydrogenation reaction conditions were: 130 °C, 10 MPa, 60 wt% coumarin in methanol, and 0.5 wt% (based on coumarin) of Ru/C catalyst. At the complete conversion of coumarin, the selectivity to the desired product was 90%.     

New coumarin derivative with potential antioxidant activity: Synthesis,DNA binding and in silico studies (Docking,MD, ADMET)

A new coumarin derivative, 7-((8-(4-benzylpiperidin-1-yl)octyl)oxy)-4-methyl-2H-chromen-2-one (C3), was synthesized by two-step alkylation reaction of 7-hydroxy-4-methyl coumarin. The structure and purity of the compound were characterized by its ¹H and ¹³C NMR, FT-IR and LC-MS spectral data. The DNA binding interaction of C3 was evaluated using UV–vis spectrophotometric and viscosimetric methods. These experiments showed that C3 was bound in intercalative mode. The antioxidant activity of C3 was evaluated by the DPPH method, the antioxidant activity results displayed that C3 had DPPH radical scavenging effect. The possible mechanism of antioxidant and anticancer activity of C3 was investigated via molecular docking by using two enzymes CYP450 and EGFR as receptors. The C3 also tended a good antioxidant ability based on the result of the molecular docking analysis, with good binding affinity values (-7.82 kcal/mol) and binding site interactions. Molecular Dynamics (MD) simulation was implemented to elucidate the interactions with the protein–ligand complex in 20 ns. The ADMET analyzes which paved the way for us to predict C3 as a drug candidate were also performed. All experimental and theoretical results showed that the compound C3 was a potential drug candidate as an antioxidant and anticancer agent.     

Thermal degradation and kinetic analysis of biodegradable PBS/multiwalled carbon nanotube nanocomposites

In this study, carbon nanotubes (CNTs) were first modified using N,N′‐ dicyclohexylcarbodiimide (DCC) dehydrating agents. Subsequently, the poly(butylene succinate)/multiwalled carbon nanotube (PBS/MWNTs) nanocomposites were prepared through facile melt blending. Thermal degradation of these PBS/MWNT nanocomposites was investigated; the kinetic parameters of degradation were calculated using the Coats and Redfern, Ozawa, and Horowitz and Metzger methods, respectively. It was found that the degradation reaction mechanism of PBS and the CNT‐C18 containing nanocomposites at lower temperature was likely to produce an F1 model through reaction of random chain cleavage (cis‐elimination). However, the reaction mechanism at higher temperature was likely to be a D1 model because of the dominant diffusion control effect. Moreover, it was found that the activation energies of CNT‐C18‐containing PBS nanocomposites were first increased with the content of CNT‐C18, but then decreased after the content was larger than 0.5 wt % for all models at differing heating rates. This may be due to the formation of a conductive network of CNTs in the polymer matrix at higher content of CNTs, which lead to better heat and electrical conductivity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1231–1239, 2009     

A comparative study of the epoxidation of 2‐substituted isoflavones by dimethyldioxirane,sodium hypochlorite,and alkaline hydrogen peroxide (weitz‐scheffer reaction)

The comparative epoxidation of 2‐substituted isoflavones 9–16 has been conducted by the utilization of three different protocols, viz. epoxidation with isolated dimethyldioxirane (Method A), with sodium hypochlorite (Method B), and with alkaline hydrogen peroxide (Method C), to afford epoxides 17–24 . Best results have been obtained with Method C (Weitz‐Scheffer epoxidation). The structures of epoxides have been assigned on the basis of nmr spectral and mass spectral data.     

Synthesis of polyetherols with isocyanuric ring. Kinetics and mechanisms of reactions,part 1: Reaction between isocyanuric acid and ethylene carbonate

The reaction between isocyanuric acid and ethylene carbonate results in the formation of polyetherols. The kinetic and mechanistic studies revealed that the initial step of the reaction is zero order related to ethylene carbonate. The rate‐limiting step is the decomposition of an intermediating dianion of ethylene dicarbonate into ethane‐1,2‐diolate dianion and carbon dioxide. Imide groups of isocyanuric acid inhibit the reaction. The mechanism of reaction was confirmed by spectroscopic methods. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 512–522, 2009     

Oxyfunctionalization products of terpenoids with dimethyldioxirane and their biological activity

Oxyfunctionalization of the bioactive terpenoids, ursolic acid acetate (1), oleanolic acid acetate (5), lupeol acetate (12), and kaurenic acid (17), with dimethyldioxirane (DMDO) was investigated. Treatment of the terpenoids with DMDO under mild conditions afforded a variety of oxidation and oxydegradation products to yield naturally occurring and/or novel compounds in one step. After chromatographic separation, the structures of the individual isolated products were determined using spectroscopic methods including several homonuclear (1H-1H) and heteronuclear (1H-13C) shift-correlated 2D-NMR techniques. The inhibitory activity of the terpenoid derivatives against alpha-glucosidase was investigated and compounds 1, 3, 7, and 9 were found to exhibit potent activity.     

Kinetics of dimethyldioxirane decomposition in the presence of cumene

Dimethyldioxirane consumption increases considerably in the presence of cumene. The product composition (cumic alcohol, acetophenone, α-methylstyrene) and the inhibiting effect of oxygen prove a radical reaction mechanism. The kinetic order for dimethyldioxirane increases with the conversion from 1.5 to 2.     

Epoxidation of homoisoflavones

A comparative study of the epoxidation of homoisoflavones (3‐benzyl‐4‐chromones) 1–4 has been performed by various oxidizing agents, víz. Epoxidation with isolated dimethyldioxirane (Method A), with alkaline hydrogen peroxide (Method B), and with sodium hypochlorite (Method C) to obtain the epoxides 4–8 . Compounds 2 and 3 have also been oxidized with a combination of dimethyldioxirane and Jacobsen's Mn(III)salen catalysts (R,R)‐11 and (S,S)‐ 11 to afford 3‐benzoyl‐4‐chromones 9 and 10 . Structures of all new compounds have been elucidated by microanalyses, ir and nmr spectroscopic measurements.     

Thermochemistry of chlorine‐containing hydrocarbons related to waste combustion

The thermochemistry of 25 chlorinated compounds potentially involved in chemical reactions related to waste combustion has been calculated using ab initio methods. Some of these species have never been reported in the literature. To check the validity of our calculations, 11 additional brominated analogues were also calculated. The thermochemical properties of these compounds were used in reaction kinetic models designed to estimate the performance of waste incinerators. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 113–122, 2009     

Oxidation of quinopimaric acid derivatives by dimethyldioxirane

Successful application of dimethyldioxirane for selective oxidation of an oxygen-containing tertiary C atom to form a hemiacetal, the preparation of which is inaccessible by other methods, was demonstrated using dihydroquinopimaric acid derivatives as examples.     

Synthesis of C3-dihydrofuran substituted coumarins via multicomponent approach

An efficient method was developed for the synthesis of dihydrofuran substituted coumarin from a one-pot, four-component reaction of 2-hydroxy aromatic aldehydes, 6-methyl, 4-hydroxy pyranone, aromatic aldehyde, and pyridinium ylide in the presence of tri-ethylamine under microwave irradiation. The reaction proceeds under solvent-free conditions to afford C3-dihydrofuran substituted coumarin in a diastereoselective manner in good yields (71–89%).     

A photo‐oxidizable kinetic pathway of three‐component photoinitiator systems containing porphrin dye (Zn‐tpp), an electron donor and diphenyl iodonium salt

A series of kinetic experiments were conducted involving visible‐light activated free radical polymerizations with three‐component photoinitiators and 2‐hydroxyethyl methacrylate (HEMA). Three‐component photoinitiator systems generally include a light‐absorbing photosensitizer (PS), an electron donor and an electron acceptor. To compare kinetic efficiency, we used thermodynamic feasibility and measured kinetic data. For this study, 5,10,15,20‐tetraphenyl‐21H,23H‐porphyrin zinc (Zn‐tpp) and camphorquinone (CQ) were used as the PSs. The Rehm‐Weller equation was used to verify the thermodynamic feasibility for the photo‐induced electron transfer reaction. Using the thermodynamic feasibility, we suggest two different kinetic mechanisms, which are (i) photo‐reducible series mechanism of CQ and (ii) photo‐oxidizable series mechanism of Zn‐tpp. Kinetic data were measured by near‐IR spectroscopy and photo‐differential scanning calorimetry based on an equivalent concentration of excited state PS. We report that the photo‐oxidizable series mechanism using Zn‐tpp produced dramatically enhanced conversions and rates of polymerizations compared with those associated with the photo‐reducible series mechanism using CQ. It was concluded from the kinetic results that the photo‐oxidizable series mechanism efficiently retards back electron transfer and the recombination reaction step. In addition, the photo‐oxidizable series mechanism provides an efficient secondary reaction step that involves consumption of the dye‐based radical and regeneration of the original PS. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3131–3141, 2009     

Dimethyldioxirane epoxidation of 3‐aryl‐1‐(3‐coumarinyl)propen‐1‐ones

Regioselective epoxidation of 3‐aryl‐1‐(3‐coumarinyl)propen‐1‐ones 1–10 by isolated dimethyldioxirane afforded the appropriate epoxides 11–20 in high (76–87%) yields.     

The kinetic regularities, products, and mechanism of the thermal decomposition of dimethyldioxirane. The contribution of molecular and radical reaction channels

The products and kinetics of the thermal decomposition of dimethyldioxirane (DMDO) were studied. The reaction proceedsvia three parallel pathways: isomerization to methyl acetate, oxygen atom insertion into the C−H bond of a solvent molecule (acetone), and the solvent-induced homolysis of the O−O bond in the DMDO molecule. The contribution of the latter reaction channel isca. 23% at 56°C. The overall kinetic parameters of DMDO thermolysis in oxygen atmosphere were determined. The free radical-induced DMDO decomposition occurs in an inert atmosphere. The formal kinetics of this reaction was investigated. The mechanism of the DMDO thermolysis is discussed. Dedicated to Professor E. T. Denisov on the occasion of his 70th Birthday. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1344–1354, August, 2000.