Kinetics and thermodynamics of the exchange reactions of peroxy radicals with hydroperoxides

The enthalpies and equilibrium constants of the exchange reactions of peroxy radicals with hydroperoxides of various structures are calculated. The experimental data on the reactions of hydrogen atom abstraction by the peroxy radicals from the hydroperoxides are analyzed, and the kinetic parameters characterizing these reactions are calculated using the intersecting parabolas method. The activation energies and rate constants for nine reactions of H atom abstraction by a peroxy radical from the OOH group of a peroxide are calculated using the above parameters. The geometric parameters of the transition states for the reactions are calculated. The low triplet repulsion plays an important role in the fast occurrence of the reactions. The polar interaction in the transition state is manifested in the reactions of the peroxy radicals with hydroperoxides containing a polar group.     

Catalytic Asymmetric Hetero-Diels-Alder Reactions of Carbonyl Compounds and Imines

Asymmetric catalysis is a challenge for chemists: How can we design catalysts to achieve the goal of forming optically active compounds? This review provides the reader with an overview of the development of catalytic asymmetric hetero-Diels-Alder reactions of carbonyl compounds and imines. Since its discovery, the Diels-Alder reaction has undergone intensive development and is of fundamental importance for synthetic, physical, and theoretical chemists. The Diels-Alder reaction has been through different stages of development, and at the beginning of the 21st century catalytic Diels-Alder reactions are one of the main areas of focus. The preparation of numerous compounds of importance for our society is based on cycloaddition reactions to carbonyl compounds and imines. There are several parallels between the reactions of carbonyl compounds and those of imines, which, however, begin to vanish on entering the field of catalytic reactions. Why? From a mechanistic point of view some similarities can be drawn, but the synthetic development of catalytic enantioselective hetero-Diels-Alder reactions of imines are several years behind those of the carbonyl compounds. For hetero-Diels-Alder reactions of carbonyl compounds there a number of different chiral catalysts, and great progress has been achieved in developing enantioselective reactions for unactivated and activated carbonyl compounds. In contrast the development of catalytic enantioselective hetero-Diels-Alder reactions of imines is in its infancy and only few catalytic reactions have been published. This review will focus on the most important developments, and discuss the synthetic and mechanistic aspects of enantioselective hetero-Diels-Alder reactions of carbonyl compounds catalyzed by chiral Lewis acids. For the hetero-Diels-Alder reactions of imines, the diastereoselective reactions of optically substrates catalyzed by Lewis acids will be presented first, followed by the catalytic enantioselective reactions.     

Synthesis of novel dendritic 2,2'-bipyridine ligands and their application to Lewis acid-catalyzed diels-alder and three-component condensation reactions

A series of dendritic ligands with a 2,2'-bipyridine core was synthesized through the coupling of 4,4'-dihydroxy-2,2'-bipyridine with poly(aryl ether) dendrons. The corresponding dendritic Cu(OTf)2 catalysts were used for Diels-Alder and three-component condensation reactions. The dendritic Cu(OTf)2-catalyzed Diels-Alder reaction proceeded smoothly, and these dendritic catalysts could be recycled without deactivation by reprecipitation. Three-component condensation reactions such as Mannich-type reactions also proceeded not only in dichloromethane but also in water. Furthermore, a positive dendritic effect on chemical yields was observed in both Diels-Alder reactions and aqueous-media three-component condensation reactions.     

Theoretical study of reaction of trifluoromethyl radical with hydroxyl and hydrogen radicals

Ab initio molecular orbital theory and density functional theory calculations have been carried out on the reactions of the trifluoromethyl radical with the hydroxyl and the hydrogen radicals. These reactions are key reactions that underlie a new fire extinguishing mechanism of non-bromine-containing halon replacements. The activation energies calculated by the MP2 and QCISD methods are in good agreement with the experimental values. The B3LYP, as well as MP2 and QCISD, give good results for the calculations of the heats of reactions. The GAUSSIAN-1 and GAUSSIAN-2 theory calculations present the most acxcurate results on both the activation energies and the heats of reactions. The effects of the scaling factors on the activation energies and the heats of reactions are also evaluated. © 1998 John Wiley & Sons, Inc. J Comput Chem 19: 277–289, 1998     

Paired Electrochemical Reactions and the On‐Site Generation of a Chemical Reagent

While the majority of reported paired electrochemical reactions involve carefully matched cathodic and anodic reactions, the precise matching of half reactions in an electrolysis cell is not generally necessary. During a constant current electrolysis almost any oxidation and reduction reaction can be paired, and in the presented work we capitalize on this observation by examining the coupling of anodic oxidation reactions with the production of hydrogen gas for use as a reagent in remote, Pd‐catalyzed hydrogenation and hydrogenolysis reactions. To this end, an alcohol oxidation, an oxidative condensation, intramolecular anodic olefin coupling reactions, an amide oxidation, and a mediated oxidation were all shown to be compatible with the generation and use of hydrogen gas at the cathode. This pairing of an electrolysis reaction with the production of a chemical reagent or substrate has the potential to greatly expand the use of more energy efficient paired electrochemical reactions.     

Hydrophobicity and mixing effects on select heterogeneous, water-accelerated synthetic reactions

The influence of aqueous reaction media on organic reactions is a topic of long-standing interest, particularly as it affects the rate or selectivity of synthetic reactions. Sometimes such reactions appear homogeneous, typically in dilute solution, whereas others are obviously heterogeneous, typically in concentrated solution that is more characteristic of a preparative synthetic reaction. The latter situation has been termed "on water." Here, it is demonstrated that the rates of heterogeneous ene reactions, Passerini reactions, and Ugi reactions in pure water and in aqueous solutions are dependent on the mixing method and reactant polarity, consistent with the involvement of hydrophobic interactions in their acceleration.     

The coordination chemistry of simple phospholes. Complexes of rhenium,ruthenium, cobalt,rhodium and iridium chlorides and of some chlorocarbonyls of ruthenium and rhodium

The reactions of 1-phenylphosphole (PP), 3-methyl-1-phenylphosphole (mPP), 3,4-dimethyl-1-phenylphosphole (dPP) and, in certain instances, 1-n-butyl-3,4-dimethylphosphole (dBP) with some transition metal chlorides and some metal-Cl-CO systems are reported. These reactions show that simple phospholes in general unexpectedly behave much like ordinary tertiary phosphines and that, unlike the reactions with Ni(II), Pd(II) and Pt(II), the complexes formed are conventional in most respects. However, a few unusual reactions were observed. For example, mPP partially reduces Ru(III) to give a mixed-valent Ru(III)-Ru(II) complex while PP reduces Ir(III) to Ir(I). From infrared spectroscopic studies of the square-planar Rh(I) complexes L₂Rh(CO) Cl (L = phosphole), it appears that donor character decreases with decreasing substitution on the phosphole ring carbon atoms. Phosphorus-phenyl cleavage has been observed in reactions of 1-phenylphosphole with Rh-CO systems. The results are briefly discussed in relation to the behaviour of other phospholes in similar reactions and in the context of the electronic structure of phospholes.     

Aminolysis of Y-substituted phenyl diphenylphosphinates and benzoates: effect of modification of electrophilic center from C=O to P=O

The effect of modification of the electrophilic center from C=O to P=O on reactivity and reaction mechanism has been investigated for aminolysis of Y-substituted phenyl diphenylphosphinates (1a-j) and benzoates (2a-i). The phosphinates 1a-j are less reactive than the benzoates 2a-i. The reactions of 2,4-dinitrophenyl diphenylphosphinate (1a) with alicyclic secondary amines resulted in a linear Br?nsted-type plot with a beta(nuc) value of 0.38, while the corresponding reactions of 2,4-dinitrophenyl benzoate (2a) yielded a curved Br?nsted-type plot. Similarly, a linear Br?nsted-type plot with a beta(lg) value of -0.66 was obtained for the reactions of 1a-j with piperidine, while the corresponding reactions of 2a-i gave a curved Br?nsted-type plot. The linear Br?nsted-type plots for the reactions of 1a-j have been taken as evidence for a concerted mechanism, while the curved Br?nsted-type plots for the reactions of 2a-i have been suggested to indicate a change in the rate-determining step of a stepwise mechanism. The Hammett plot for the reactions of 1b-j exhibited a poor correlation with sigma(-) constants (R(2) = 0.962) but slightly better correlation with sigma(o) (R(2) = 0.986). However, the Yukawa-Tsuno plot for the same reactions resulted in an excellent correlation (R(2) = 0.9993) with an r value of 0.30. The aminolysis of 1a-j has been suggested to proceed through a concerted mechanism with an early transition state on the basis of the small beta(nuc) and small r values.     

Rapid evaluation and screening of interfacial reactions on self-assembled monolayers

This paper reports 16 chemical reactions for elaborating the structures of self-assembled monolayers (SAMs) of alkanethiolates on gold. This work takes advantage of matrix-assisted laser desorption/ionization and time-of-flight mass spectrometry (MALDI-TOF MS) to rapidly characterize the products and yields of reactions that occur with molecules attached to monolayers. The paper also describes a method for screening reaction conditions, wherein monolayers are treated with an array of reactants and mass spectrometry is used to identify those regions that undergo reactions to give new, and unanticipated, products in high yield. These examples serve to increase the collection of reactions that can be used to elaborate the structures, and therefore the properties, of self-assembled monolayers of alkanethiolates on gold and to introduce label-free methods for screening interfacial reactions.     

Cycloadditions and annulations of transition metal carbene complexes

The synthetic aspects of several reactions from the multifaceted chemistry of Fischer carbene complexes are examined. Their benzannulation reactions with acetylenes are utilized in the synthesis of anthracyclinones via two approaches which differ by beginning at opposite ends of the molecule with either an aryl or an alkenyl substituted chromium carbene complex. The latter has been employed in a formal synthesis of daunomycinone. The Diels-Alder reactions of ,β-acetylenic chromium carbene complexes provide for a facile entry into substituted cyclohexenyl chromium carbene complexes that are subsequently employed in benzannulation reactions. These tandem cycloaddition/annulation reactions are incorporated into model studies for the synthesis of anthracyclinones and wentilactone A. Their potential is also demonstrated for coupling to yet a third reaction of organochromium compounds ; aromatic nucleophilic substitutions on arene chromium tricarbonyl complexes. The annulations of β,β-disubstituted alkenyl complexes provides for a regio- and stereoselective synthesis of 2,4-cyclohexadienones under neutral conditions at near ambient temperatures.     

Properties and reactions of charged species in nonpolar supercritical fluids

This review focuses on the properties and reactions of charged species in supercritical fluids. The techniques of pulse conductivity and transient absorption are used to follow the behavior of charged species. We begin with a discussion of the mobilities, yields, and energy levels of electrons. Studies of the pressure dependence of electron attachment reactions lead to information on the magnitude of activation volumes. This as well as diffusion and energetics are factors that influence the rates of electron attachment. The free energy changes in electron attachment-detachment equilibrium reactions decrease rapidly at pressures where the compressibility maximizes. The transport properties of ions in supercritical fluids are also discussed, as these studies provide a straightforward indication of the degree of interaction between ions and the medium. We conclude with a review of electron transfer reactions in supercritical fluids.     

Direct and quantitative monitoring of catalytic organic reactions under heterogeneous conditions using direct analysis in real time mass spectrometry

This new method overcomes problems of conventional analytical methodologies such as light scattering and sampling reproducibility issues. We used this method for mechanistic studies of catalytic reactions under heterogeneous conditions. Direct-type hydroxymethylation reactions and Mukaiyama-type hydroxymethylation reactions both catalyzed by a scandium–bipyridine ligand complex under micellar conditions were employed as examples of heterogeneous reactions. For direct-type hydroxymethylation reactions, initial reaction rate assays revealed first-order dependency on both substrate and catalyst. On the other hand, Mukaiyama-type hydroxymethylation reactions showed first-order rate dependency on substrate, zero-order on catalyst and saturation kinetics on formaldehyde.

A direct and quantitative method for monitoring heterogeneous organic reactions has been developed by using direct analysis in real time mass spectrometry (DART-MS) with an isotope-labeled reaction product as an internal standard.     

手性pybox-金属络合物及其在不对称催化反应中的应用

具有C2对称性的双噁唑啉型吡啶(pybox)是一类有效的手性配体,能与许多金属离子配位,其手性催化性能已得到越来越多的关注。本文综述了手性配体pybox和pybox-金属络合物的合成方法,特别是近年来pybox-金属络合物在不对称催化反应如不对称环丙烷化反应、不对称Diels-Alder反应、1,3-偶极环加成反应、不对称aldol反应等中应用的最新进展。     

Interactions and reactions of monolayers and Langmuir-Blodgett multilayers with compounds in the bulk phase

Studies performed on the interactions and reactions of compounds in the bidimensional state, essentially in monolayers and Langmuir-Blodgett multilayers, with substances in the aqueous subphase are reported. More precisely, the following is illustrated: (i) interactions between acid amphiphiles and prevalently bivalent ions placed in the aqueous support and between compounds capable of functioning like ion carriers in monolayers and ions in the subphase, in order to build mimetic membranes capable of selective ion transport; and the complexation of amphiphiles in monolayer with ions in the bulk liquid phase, in order to build chemical sensors to ions; (ii) the reactions of photoinduced electron transfer between a partner in mono- or multimolecular films and a partner in the subphase, which may determine the fundamental parameters and the differences with the same reactions in the bulk phase; and (iii) the reactions of enzymatic hydrolysis between the monolayer of a glyceride, which constitutes the reaction support, and the enzyme in the liquid bulk phase, which constitutes the subphase. The mechanism of the reactions and its inhibition are clarified. To conclude, possible future developments connected with the areas studied are examined.     

Rapid chemical separations for thermal neutron activation analysis of niobium and vanadium and application to controlled thermonuclear reactor materials studies

Interfering reactions in photon activation analysis are compiled and evaluated quantitatively; the results are based on experimentally obtained data exclusively. All elements in the Periodic Table with few exceptions have been irradiated several times with 30 MeV bremsstrahlung produced by a linear electron accelerator. The element samples were measured many times to detect all expected radionuclides and hence all possible interfering reactions. These reactions are listed and presented in Table 1.     

Mechanisms of hydrogen-, oxygen-, and electron-transfer reactions of cumylperoxyl radical

Rates of hydrogen-transfer reactions from a series of para-substituted N,N-dimethylanilines to cumylperoxyl radical and oxygen-transfer reactions from cumylperoxyl radical to a series of sulfides and phosphines have been determined in propionitrile (EtCN) and pentane at low temperatures by use of ESR. The observed rate constants exhibit first-order and second-order dependence with respect to concentrations of N,N-dimethylanilines. This indicates that the hydrogen- and oxygen-transfer reactions proceed via 1:1 charge-transfer (CT) complexes formed between the substrates and cumylperoxyl radical. The primary kinetic isotope effects are determined by comparing the rates of N,N-dimethylanilines and the corresponding N,N-bis(trideuteriomethyl)anilines. The isotope effect profiles are quite different from those reported for the P-450 model oxidation of the same series of substrates. Rates of electron-transfer reactions from ferrocene derivatives to cumylperoxyl radical have also been determined by use of ESR. The catalytic effects of Sc(OTf)(3) (OTf = triflate) on the electron-transfer reactions are compared with those of Sc(OTf)(3) on the hydrogen- and oxygen-transfer reactions. Such comparison provides strong evidence that the hydrogen- and oxygen- transfer reactions of cumylperoxyl radical proceed via a one-step hydrogen atom and oxygen atom transfer rather than via an electron transfer from substrates to cumylperoxyl radical.     

Reactivity of Grubbs' catalysts with urea- and amide-substituted olefins. Metathesis and isomerization

[Chemical reaction: see text] The reactions of a series of urea- and amide-substituted olefins with Grubbs' catalysts are presented. Depending on the substrate's nature, the formation of either cross-metathesis or isomerization products is observed. To favor the cross-metathesis products, the reactions have been carried out using a wide range of experimental conditions. Upon addition of monophenyl phosphoester to these reactions, the isomerization of the olefins is completely suppressed and the cross-metathesis products are obtained in up to 60% yield.     

硅杂苯与亲二烯体的Diels-Alder反应

采用密度泛函理论(DFT)在B3LYP/6-311G(d,p)水平上研究了硅杂苯与一些亲二烯体的两类可能的Diels-Alder反应的微观机理、势能剖面、取代基效应和溶剂化效应. 计算结果表明, 所研究反应均以协同的方式进行. 亲二烯体分子碳原子上的苯基取代基对两个新键形成的非同步性和反应的活化能垒的影响取决于苯基在产物中的相对位置, 而硅杂苯分子中硅原子上的CCl3取代基有利于杂Diels-Alder反应的进行. 形成一个C—Si键的杂Diels-Alder反应在热力学和动力学上均远比相应的全碳Diels-Alder反应容易进行, 实验观察到的杂Diels-Alder反应中的区域选择性由动力学因素所控制. 硅杂苯与烯烃的反应比与相应炔烃的反应在动力学上容易进行一些, 但在热力学上后者远比前者容易进行. 苯溶剂对所研究反应的势能剖面影响较小.     

Coupling Reaction of Organoboronic Acids with Chloropyrimidines and Trichlorotriazine

Pd-catalyzed cross-coupling reactions of chloropyrimidirtes with alkenylboronic acids readily proceed to give the corresponding alkenylpyrimidines in high to excellent yields. The coupling reaction of 2,4-dichloropyrimidine or 2,4,6-trichloropyrimidine with one equivalent of alkenylboronic acid occurred more easily on 4-position than on 2-position, which implied that the reaction is highly regioselective. The reaction is stereospecific since the configuration of C=C remained intact. The preliminary study on the cross-coupling reactions of 2,4,6-trichlorotriazine with one equivalent of arylboronic acids showed that the reactions afforded the monosubstituted triazines in moderate yields. The effect of steric hindrance of the substitutents on the reactions was found.     

Chemical Reactions of Coumarins and Furocoumarins on Thin-Layer Chromatoplates

Most of the reaction achieved in this work were conducted with coumarin and furocoumarin. The reactions were performed on inert thin-layer chromatoplates under controlled conditions and the products of the reactions were compared as usual with the expected substances on the same chromatogram. The reactions performed were: mineral acid hydrolysis, methylation, acetylation, benzoylation, nitration and Schiff's bases on silica gel chromatoplates.