A concerted hydrogen-transfer reaction in the gas phase

The kinetics of the thermal reaction of mixtures of ethylene and cyclopentene has been examined for the occurrence of a concerted hydrogen-transfer reaction, . The main products of the reaction were ethane and cyclopentadiene, and the rate of formation of ethane was first order in each reactant over a 2500-fold change in the ratio of concentrations of the reactants. An increased surface-to-volume ratio of the reaction vessel or additions of oxygen and nitric oxide had little effect on the rate of formation of ethane, and it was concluded that the dominant reaction in the system was the concerted hydrogen-transfer process. The rate constant for the reaction, measured over the temperature range of 325–505°C, was represented as      

Explorations into new reaction chemistry

This Review describes the basic concepts that have guided our exploration of new chemical reactions by giving examples of results from my research group. Our strategy of carrying out research is to investigate three to four different topics at a time so we can gather as many results as possible. These may at first appear unrelated to each other but may have the potential to be united into a greater hypothesis after repeated feedback. Three scenarios from our research are presented: the "oxidative-reductive condensation reaction" devised in 1960, which after an interval of nearly 40 years brought forth the new concept of using compounds of structure Ph(2)POR as reducing reagents; the "TiCl(4)-aldol reaction" of 1973 that eventually led to the present "base-promoted aldol reaction" through a chain of ideas; and the "glycosylation reaction using fluorosugars" from 1984 which recently bloomed into "stereocontrolled glycosylation". Thus, it can be said that by reviewing what we had done before, we were able to expand on it to achieve new outcomes.     

String model of chemical reaction coordinate

A geometrical model for estimating the effects of external fields upon a reaction path is proposed. The reaction path is defined as the intrinsic reaction coordinate (IRC) which is treated as a string. The IRC frame is introduced in order to uniquely determine the attitude of the string with respect to the reaction medium. The string is thrown in the external fields of the reaction medium, and slides or rotates, and is deformed. The cell structure attached to the string is also deformed. A perturbational approach to the reaction rate formula is presented.     

Grignard reaction with 2, 6-dialkoxydihydro- and -tetrahydropyrans

The Grignard reaction with 2, 6-dialkoxytetrahydropyran and 2, 6-dialkoxy-5, 6-dihydro-2H-pyran has been studied. In both cases the reaction takes place with the opening of the pyran ring and the formation of alkoxy-substituted saturated or , -unsaturated alcohols.During the complption of our work, a paper appeared in which the Grignard reaction with 2, 6-diethoxytetrahydropyran was studied [1].     

Graphene layer growth chemistry: five- and six-member ring flip reaction

Reaction pathways are presented for hydrogen-mediated isomerization of a five- and six-member carbon ring complex on the zigzag edge of a graphene layer. A new reaction sequence that reverses the orientation of the ring complex, or "flips" it, was identified. Competition between the flip reaction and the "ring separation" was examined. Ring separation is the reverse of the five- and six-member ring complex formation reaction, previously reported as "ring collision". The elementary steps of the pathways were analyzed using density functional theory (DFT). Rate coefficients were obtained by solution of the energy master equation and classical transition-state-theory utilizing the DFT energies, frequencies, and geometries. The results indicate that the flip reaction pathway dominates the separation reaction and should be competitive with other pathways important to the graphene zigzag edge growth in high-temperature environments.     

Halo-2-pyrones in the Ullmann reaction. 1

The Ullmann reaction was used for the first time for the synthesis of poly-2-pyrones. 3-Halo-2-pyrones were obtained by halogenation of the corresponding 6-aryl-2-pyrones. The Ullmann reaction was carried out by heating a mixture of the 3-halo-2-pyrone with activated copper in a stream of an inert gas. The reaction products were the previously undescribed bis-2-pyrones, in which the -pyrone rings are interlinked by means of the 3-C atoms.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 173–176, February, 1979.     

Identifiability of chemical reaction networks

We consider the dynamics of chemical reaction networks under the assumption of mass-action kinetics. We show that there exist reaction networks for which the reaction rate constants are not uniquely identifiable, even if we are given complete information on the dynamics of concentrations for all chemical species of . Also, we show that there exist reaction networks such that their dynamics are identical under appropriate choices of reaction rate constants, and present theorems that characterize the properties of , , that make this possible. We use these facts to show how we can determine dynamical properties of some chemical networks by analyzing other chemical networks.     

Reexamination of the traditional Baylis-Hillman reaction

In the Baylis-Hillman reaction of arylaldehydes with methyl vinyl ketone (MVK), we found that, besides the normal Baylis-Hillman adduct 1, the diadduct 2 can also be formed at the same time and the yield of 2 can reach to 55% if increasing the amount of methyl vinyl ketone. But for ethyl vinyl ketone (EVK), methyl acrylate or acrylonitrile, only the normal Baylis-Hillman adduct 4, 7 or 8 was obtained, respectively. The substituent's effects and Lewis base effects were also examined and a plausible reaction mechanism was proposed for the formation of 2.     

Extended hessian matrix along the reaction coordinate

We shall prove by the coordinate-free covariant treatment that the vibrational frequency along the reaction coordinate is exactly given by the extended Hessian matrix in a rigged configuration space where the reaction coordinate is identified with a straight line. The diagonalization of the extended Hessian matrix is straightforward with no recourse to the prescribed procedure of eliminating the coupling matrix elements between the promoting mode of chemical reaction and the vibrational modes.     

A boundary-driven reaction front

A model reaction scheme in which two species $A$ and $B$ react to form an inert product is considered, with the possible linear decay of $A$ to a further inert prduct also included. The reaction between $A$ and $B$ is maintained by the input of $A$ from the boundary which keeps $A$ at a constant concentration. The cases when $B$ is immobile or free to diffuse are treated. In the former case reaction fronts in $B$ are seen to develop. Large time asymptotic solutions are derived which show that these fronts propagate across the reactor at rates proportional to $t^{1/2}$ or $\log t$ ( $t$ is a dimensionless time) depending on whether the extra decay step is included. A similar situation is seen when $B$ can diffuse when the linear decay step is not present. However, when this extra step is included in the reaction scheme the reaction zone reaches only a finite distance fronm the boundary at large times.     

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.     

Study of the kinetics of the Chichibabin reaction

The rate of hydrogen and ammonia evolution during the amination of N-heteroaromatic systems with sodium amide was studied. The ease of the Chichibabin reaction of heterocycles decreases in the following order: 1-methylbenzimidazole > isoquinoline > 1-methylperimidine > benzo[f]quinoline > pyridine acridine. The decrease in the rate of amination in the presence of free-radical inhibitors constitutes evidence for a free-radical step in the Chichibabin reaction. It is shown that the Chichibabin reaction has autocatalytic character and is accelerated in the presence of sodium salts of heterylamines. Opinions regarding the mechanism of this autocatalysis are expressed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 244–252, February, 1976.     

过渡金属催化的炔烃复分解反应

综述了过渡金属均相催化的炔烃复分解反应进展,主要分为两部分：一是炔烃复分解反应在炔烃合成中的应用,即从六、七十年代Mortreux催化剂的发现能均相催化炔烃的歧化反应,经过一系列的条件改造,合成了炔醚和二芳基乙炔等化合物,并提出了可能的两种机理：金属卡宾和金属卡拜机理;金属钼和钨的卡拜络合物相继合成,发现此类络合物能够催化官能化的二炔的复分解反应,合成一系列的大环化合物。二是炔烃复分解反应在合成高聚物中的应用,即钙和钨的卡拜络合物被用来催化ROMP和ADIMET反应合成高聚物,改良了的Mortreux催化剂也能催化高聚物的生成,这些高聚物在发光器件、有机"塑料"激光、液晶显示器上都有应用。     

Quantum chemical reaction networks,reaction graphs and the structure of potential energy hypersurfaces

Global properties of the Born-Oppenheimer energy expectation value functional, defined over the nuclear configuration space R, are analyzed. Quantum chemical reaction graphs and reaction networks are defined in terms of intersection graphs of connected sets of nuclear geometries, representing various chemical structures. The set of all possible reaction mechanisms on the given energy hypersurface and the associated activation energy conditions are analyzed using reachability matrices defined over digraphs D ^s() and D ^s(, E).     

The pyrolysis of neopentane at small extents of reaction

The pyrolysis of neopentane, at small extents of reaction, was studied by gas chromatography, in Pyrex reaction vessels between 450° and 530°C and in the initial pressure range 25–200 mm Hg. At initial time, this thermal decomposition can be essentially represented by a homogeneous long-chain radical mechanism. The rate constant of the unimolecular initiation process is approximately given by the expression The initial rate constant of the global reaction (order 3/2) is nearly equal to This reaction is strongly inhibited by propene or isobutene and self-inhibited by the isobutene formed; an interpretation of all these inhibition phenomena of the neopentane pyrolysis is proposed. Our observations and conclusions, which have been summarized in communications during 1968 and 1969, are compared to those of other authors, particularly to the recent ones of Purnell and colleagues [13] and of Taylor and colleagues [14], [15].     

MNDO study of reaction paths: Diboration of acetylene

The reaction of B₂H₄ with acetylene has been studied by the MNDO method. It is shown that the reaction is exothermic and proceeds in two steps. The first step is the formation of a three-center -complex and this is the rate-determining step of the reaction. The second step is the rearrangement of the -complex to the product and this step requires a very small amount of activation energy. The activation barrier for the diboration reaction is 12.8 kcal/mol.The proposed mechanism is significantly different from those proposed earlier and explains all experimental data relating to this reaction.     

Task-specific ionic liquid as base, ligand and reaction medium for the palladium-catalyzed Heck reaction

A novel ionic liquid, which was based on ethanolamine-functionalized quaternary ammonium salt was designed and synthesized. 4-Di(hydroxyethyl)aminobutyl tributylammonium bromide (DHEABTBAB) 1, a task-specific ionic liquid, which acts as a base, ligand and reaction medium, exhibits a very high activity and recyclability to palladium-catalyzed Heck reaction. The olefinations of iodoarenes, bromoarenes and chloroarenes with olefins generated the corresponding cross-coupling products in good to excellent yields only in the presence of DHEABTBAB and palladium acetate under phosphine-free reaction conditions. It is noteworthy that palladium and DHEABTBAB could be repeatedly recycled and reused for six consecutive trials without significant loss of their activities.     

Microwave assisted synthesis of dihydropyrrole by AgOAc catalyzed intramolecular cyclization reaction of homopropargyl amine

A series of 5-aryl dihydropyrrole was synthesized from the intramolecular cyclization reaction of homopropargyl amine in the presence of AgOAc as catalyst under microwave irradiation reaction conditions. The homopropargyl amine was prepared by the reaction of propargyl bromide with N-tosyl aldimine under a sonochemical Barbier-type reaction condition. Further aromatization reaction of 5-aryl dihydropyrrole in KOtBu/DMSO can afford 2-aryl pyrrole under microwave irradiation reaction conditions.     

Tandem postsynthetic modification of metal-organic frameworks using an inverse-electron-demand Diels-Alder reaction

A postsynthetic modification (PSM) scheme for metal-organic frameworks (MOFs) has been developed using a tetrazine-based "Click" reaction. It was found that the efficacy of this modification procedure was dependent on the MOF topology and, in the case of an isoreticular MOF (IRMOF) system, required the formation of a mixed-ligand IRMOF with a suitable ratio of 1,4-benzenedicarboxylate (BDC) and an olefin-tagged BDC derivative. On the basis of the versatile use of tetrazine "Click" chemistry in bioconjugate chemistry, we expect that this scheme will prove to be a useful reaction for preparing functionalized materials, including MOFs.     

Anticatalytic microdetermination of mercury using cerium-arsenite reaction

Summary An anticatalytic kinetic method, based on the decreased rate of the reaction between Ce(IV) and As (III), was developed for the determination of mercury. The change in reaction rate due to inhibition by mercury was measured spectrophotometrically at 275 nm. Reaction conditions and interferences of foreign ions were studied. Amounts of mercury in the range 0.04–0.20g were determined with an overall error of less than 5 % at a reaction time of 25 minutes.

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Zusammenfassung Eine antikatalytische, kinetische Methode zur Quecksilberbestimmung wurde ausgearbeitet, die auf der Hemmung der Cer(IV)-As(III)-Reaktion beruht. Die Veränderung der Reaktionsgeschwindigkeit wird spektrophotometrisch bei 275 nm gemessen. Die Reaktionsbedingungen und die Störung durch Fremdionen wurden geprüft. 0,04–0,20g Hg wurden mit einem Gesamtfehler von weniger als 5% innerhalb 25 min. bestimmt.