Monitoring reaction intermediates in the FeCl3-catalyzed michael reaction by nuclear inelastic scattering

We present a study of the metal-centered vibrations in the first step of the Fe(III)-catalyzed Michael reaction. Nuclear inelastic scattering of synchrotron radiation was carried out on a shock-frozen solution of FeCl3.6H2O in 2-oxocyclopentane ethylcarboxylate (CPEH), as well as on the solid reference compounds FeCl3.6H2O, [N(CH3)4][FeCl 4], and Fe(acac) 3. In addition to the vibrations of the FeCl4(-) anion at 133 and 383 cm(-1), a multitude of modes associated with the complex Fe(CPE)2(H2O)2 could be identified. Normal-mode analysis on different isomers of the simplified model complex Fe(acac)2(H2O)2 as well as that of the full complex carrying two entire CPE ligands was carried out using density functional calculations. Comparison with experiment suggests that the facial bis(diketonato) isomer probably dominates in the reaction mixture. Thus, we have identified for the first time the isomeric structure of an iron-based intermediate of a homogeneous catalytic reaction using nuclear inelastic scattering.     

2-aminothiophenes by the gewald reaction

The review presents the most elegant and promising set of synthetic routes for the synthesis of 2-aminothiophenes by the Gewald reaction. Applications of this facile methodology to pharmaceuticals and dyestuffs have been demonstrated.     

Mechanisms of the water-gas-shift reaction by iron pentacarbonyl in the gas phase

We analyzed the mechanisms of the water-gas-shift reaction catalyzed by Fe(CO) 5/OH (-) in the gas phase using DFT methods. The systematic analysis of the accessible reaction mechanisms and the consideration of the Gibbs free energies allows for different reaction routes than previously suggested. In the dominant catalytic cycle, the hydride [FeH(CO) 4]- is the important intermediate. Associative reaction mechanisms are not favorable under moderate and low pressures. At high pressure, a side reaction takes over and prevents the conversion of H 2O and CO to H 2 and CO 2 and leads to the formation of HCOOH.     

Synthesis of photocrosslinkable polyesters by the Knoevenagel reaction

A new group of photocrosslinkable polyesters formed by the Knoevenagel reaction is described. The approach permits preparation of photoesensitive polymers, where physical properties can be potentially varied through choice of the polyol and the dicarboxylic acid. The following compounds were prepared and studied: (1) products from a Knoevenagel reaction of poly(trimethylopropane azelate cyanoacetate) with benzaldehyde, furaldehyde, and 2-ethylbutyraldehyde and (2) products from a Knoevenagel reaction of poly(1,3-propyl malonate) with benzaldehyde, p-methoxybenzaldehyde, and 2-ethylbutyraldehyde. Conventional unsaturated polyesters such as poly(1,3-propyl fumarate) and poly(1,3-propyl maleate) were prepared and used for comparison.     

Asymmetric syn-selective Henry reaction catalyzed by the sulfonyldiamine-CuCl-pyridine system

A catalytic asymmetric Henry reaction has been developed with use of a sulfonyldiamine-CuCl complex as a catalyst. A series of new binaphthyl-containing sulfonyldiamine ligands (2a-h) were readily synthesized in two steps starting from commercially available chiral 1,2-diamines. The (R,R)-diamine-(R)-binaphthyl ligand (2d)-CuCl complex smoothly catalyzed the enantioselective Henry reaction with the assistance of pyridine to give the corresponding adduct with high enantiomeric excess (up to 93%). Moreover, the 2d-CuCl-pyridine system promotes the diastereoselective Henry reaction in syn-selective manner to give the adduct in up to 99% yield with 92:8 syn/ anti selectivity. The enantiomeric excess of the syn-adduct was 84% ee.     

Theoretical study on the reaction mechanism of NO and CO catalyzed by Rh atom

The gas-phase reaction mechanism of NO and CO catalyzed by Rh atom has been systematically investigated on the ground and first excited states at CCSD(T)//B3LYP/6-311+G(2d), SDD level. This reaction is mainly divided into two reaction stages, NO deoxygenation to generate N₂O and then the deoxygenation of N₂O with CO to form N₂ and CO₂. The crucial reaction step deals with the NO deoxygenation to generate N₂O catalyzed by Rh atom, in which the self-deoxygenation of NO reaction pathway is kinetically more preferable than that in the presence of CO. The minimal energy reaction pathway includes the rate-determining step about N–N bond formation. Once the NO deoxygenation with CO catalyzed by rhodium atom takes place, the reaction results in the intermediate RhN. Then, the reaction of RhN with CO is kinetically more favorable than that with NO, while both of them are thermodynamically preferable. These results can qualitatively explain the experimental finding of N₂O, NCO, and CN species in the NO + CO reaction. For the N₂O deoxygenation with CO catalyzed by rhodium atom, the reaction goes facilely forward, which involves the rate-determining step concerning CO₂ formation. CO plays a dominating role in the RhO reduction to regenerate Rh atom. The complexes, OCRhNO, RhON₂, RhNNO, ORhN₂, RhCO₂, RhNCO, and ORhCN, are thermodynamically preferred. Rh atom possesses stronger capability for the N₂O deoxygenation than Rh⁺ cation.     

The reaction of selenoaldehydes with 2-methoxyfuran using their generation by retro Diels-Alder reaction

Selenoaldehydes, regenerated by thermal retro Diels-Alder reaction of anthracene cycloadducts under neutral conditions, reacted with 2-methoxyfuran to give methyl penta-2,4-dienoates along with the deposition of elemental selenium. In a similar reaction with 2-methoxyfuran using thioaldehyde, thiirane compound was isolated. This suggests the formation of selenirane intermediates in the above reaction.     

Catalytic reaction accompanied by capillary condensation, 3. Influence on reaction kinetics and dynamics

The influence of capillary condensation of reagents on the catalytic reaction kinetics and dynamics was studied. The hydrogenation ofp-xylene over Pt/SiO₂ was used as a model reaction. Two types of SiO₂ were used (KCK-1 with large pores and KCM-5 with small pores). It was shown that capillary condensation could modify the kinetics and the transition regimes. The proposed mathematical model demonstrates good agreement with experimental results for both steady-state and dynamic regimes, including reaction rate—temperature hysteresis.     

Synthesis of N-propargylanabasine derivatives by the mannich reaction

N-Propargylanabasine derivatives bearing various substituents at the carbon atom of the alkyne fragment were obtained by the reaction of anabasine hydrochloride with terminal alkynes and paraformaldehyde. The reaction proceeded with retention of the C(2) chiral center in anabasine fragment. The by-products of the reaction, including 1,3-diacetylene (the products of dimerization of alkynes) and conjugated vinylacetylenes (the rearrangement products of the Mannich adducts) were isolated and characterized. Dedicated to Academician V. A. Tartakovsky in honor of his 75th anniversary. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1576–1585, August, 2007.     

Zeolites in the synthesis of quinolines by the Skraup reaction

Russian Chemical Bulletin - A novel heterogeneous catalytic method for the synthesis of quinoline (1) and a mixture of 2- and 4-methylquinolines (2) by Skraup reaction in the presence of H-Y,...     

The generation of gem-difluoroallyllithium by the transmetalation reaction

3,3-Difluoroallyltrimethyltin was prepared by reaction of chlorodifluoromethane with the ylide reagent Ph₃PCHCH₂SnMe₃$\text{gem}$-Difluoroallyllithium, which was generated by the reaction of $\text{n}$-butyllithium with 3,3-difluoroallyltrimethyltin in THF at ?95°, was of very limited stability at that temperature. However, $\text{in}$$\text{situ}$ procedures and alternate incremental addition procedures allowed its application in the synthesis of 1,1-difluoroallylsilanes from chlorosilanes and of CH₂CHCF₂C(OH)-Et₂ from 3-pentanone.     

Kinetics of the reaction between 1,3-diphenylisobenzofuran and nitrogen dioxide studied by steady-state fluorescence

1,3-Diphenylisobenzofuran (DPBF) is a fluorescent molecule which is believed to react highly specifically toward reactive oxygen species such as singlet oxygen (¹O₂), hydroxy (HO^·), alkyloxy (RO^·), and alkylperoxy (ROO^·) radicals. In all cases the reaction product is 1,2-dibenzoylbenzene. In order to prove that DPBF gives the same product in contact with reactive nitrogen species, its reaction with nitrogen dioxide radical has been studied in 2,2,4-trimethylpentane using the steady-state fluorescence method and mass spectrometry. The progress of the studied reaction was measured by observation of changes in fluorescence intensity of DPBF after addition of nitrogen dioxide (NO₂). The rate constants of DPBF fluorescence decay affected by NO₂ have been determined. Experiments were conducted over the temperature range of 13–37 °C and for NO₂ concentrations from 0.02 to 0.14 mmol dm^?3. It has been found that the reaction between 1,3-diphenylisobenzofuran and nitrogen dioxide proceeds in two steps. The first step is a very rapid reaction whose rate could not be measured under established experimental conditions. The second step is slower. The reaction product was identified by registration of mass spectra. The probable reaction mechanism is proposed.     

Synthesis of monohalocyclopropane derivatives from olefins by the reaction with trihalomethanes and copper

Fluoro-, chloro-, bromo-, and iodocyclopropane derivatives were obtained in 10–80% yields by the reaction of FCHI₂, ClCHI₂, BrCHI₂, and CHI₃, respectively, with Cu in the presence of olefins. The reaction was electrophilic, and proceeded stereospecifically, i.e., cis and trans olefins afforded cyclopropane derivatives whose configurations with respect to the substituents from original olefins were cis and trans, respectively. Since isomeric olefins were not detected in the reaction mixture which would be expected from the insertion of the corresponding free monohalocarbenes into C—H bonds, the reaction seemed to proceed via organocopper intermediates rather than free monohalocarbenes. With respect to the configuration of the halogen introduced by the new reaction, the cis or endo isomers were generally obtained predominantly over the corresponding trans or exo isomers.     

Kinetics and mechanism of the NCN + NO2 reaction studied by experiment and theory

The rate constant for the NCN + NO 2 reaction has been measured by a laser photolysis/laser-induced fluorescence technique in the temperature range of 260-296 K at pressures between 100 and 500 Torr with He and N 2 as buffer gases. The NCN radical was produced from the photolysis of NCN 3 at 193 nm and monitored by laser-induced fluorescence with a dye laser at 329.01 nm. The rate constant was found to increase with pressure but decrease with temperature, indicating that the reaction occurs via a long-lived intermediate stabilized by collisions with buffer gas. The reaction mechanism and rate constant are also theoretically predicted for the temperature range of 200-2000 K and the He and N 2 pressure range of 10 (-4) Torr to 1000 atm based on dual-channel Rice-Ramsperger-Kassel-Marcus (RRKM) theory with the potential energy surface evaluated at the G2M//B3LYP/6-311+G(d) level. In the low-temperature range (<700 K), the most favorable reaction is the barrierless association channel that leads to the intermediate complex (NCN-NO 2). At high temperature, the direct O-abstraction reaction with a barrier of 9.8 kcal/mol becomes the dominant channel. The rate constant calculated by RRKM theory agrees reasonably well with experimental data.     

The detailed mechanism of the Dushman reaction explored by computer

Since 1926 investigations of the Dushman reaction have relied mainly upon “constant-rate” measurements, usually by instrumental methods. Since about that time, the confusion surrounding this venerable reaction has been growing. In part, the confusion arises because the reaction involves reactive intermediate species that have not been studied directly—and may never be. Alternative detailed mechanisms have been assumed with little restraint. One of these, which is built around H₂I₂O₃, has been explored by computer with promising results. The mechanism seems capable of reducing the confusion now attending the Dushman reaction and others related to it.     

Copper- and ligand-free Sonogashira reaction catalyzed by palladium in microemulsion

An oil-in-water microemulsion containing PdCl2 and NaOH can be used as an effective catalyst system for rapid copper- and ligand-free Sonogashira reaction of aryl halides and phenylacetylene. Excellent yield of the Sonogashira reaction catalyzed by 0.5 mol% palladium could be achieved within 5 min. The types of base have an intense influence on the reaction. The reaction rate was increased with increased aqueous content in the microemulsions, and dispersed palladium nanoparticles can be in situ formed without other reductants.     

Pseudo-potentiostatic electrolysis by potential buffering induced by the oxygen evolution reaction

A new approach is proposed in order to perform electrochemical oxidation of organics by working under galvanostatic conditions with the potential ‘buffered’ by the competing side reaction of oxygen evolution (OER). According to this process the working potential is fixed by the nature of electrode material and is buffered during organics oxidation by the side reaction of OER. This principle has been used for the selective oxidation of some model organic compounds on Ti/IrO₂ anode.     

Reaction between carbon dioxide and propylene oxide catalyzed by cobalt and chromium porphyrin complexes: The effect of reaction conditions on the reaction rate

The effect of the conditions (time, temperature, pressure, and cocatalyst/catalyst ratio) on the rate and selectivity of the reaction between СО₂ and propylene oxide catalyzed by TPPCrCl and TPPCoCl (TPP is 5,10,15,20-tetraphenylporphyrin) has been studied. The time variation of the reaction rate has been analyzed by measuring the СО₂ uptake during the reaction. The observed dependences of the reaction rate on the temperature and cocatalyst/catalyst ratio are similar for TPPCrCl and TPPCoCl. In the presence of TPPCoCl, the reaction yields a mixture of poly(propylene carbonate) and a cyclic carbonate, while when TPPCrCl is used, only the cyclic carbonate is synthesized.     

Isotope separation by laser-enhanced chemical reaction

Reactivity enhancement was studied using a reaction between a laser excited atomic beam and a molecular beam. This method was applied to lithium isotope separation, in which the excited Li isotopic atom reacts with CHCIF₂. It is found that the specified lithium isotope is enriched in the reaction product LiF, whereas LiCl has no selectivity.