Solventless and Metal‐Free Synthesis of High‐Molecular‐Mass Polyaminoboranes from Diisopropylaminoborane and Primary Amines

The solventless reaction of diisopropylaminoborane with n‐butylamine, at room temperature, leads to a mixture of B_(sp2)H‐, B_(sp3)H₂‐, and B_(sp3)H₃‐containing species. At low temperature, the reaction outcome is completely modified, thus leading selectively to the formation of high‐mass polybutylaminoborane. When extended to a variety of primary amines, under solventless conditions and at low temperature, this reaction provides a new, efficient, and direct metal‐free access to high‐molecular‐mass polyaminoboranes in good to high yields under mild reaction conditions.     

Catalytic Decomposition of H2O2over Supported ZnO

 Transition metal sulfates of Cu(II), Co(II), Ni(II), Cr(III), Mn(II), and Fe(III) supported on ZnO were prepared and characterized by SEM, EDX, and XRD. The kinetics of the heterogeneous decomposition of H₂O₂ over these supported catalysts was investigated. The reaction rate is correlated with both the amount of supported metal ion and its redox potential. The rate of reaction increases with increasing initial concentration of H₂O₂, attains a maximum, and decreases thereafter. It also increases with pH and reaches a maximum at high pH values. A reaction mechanism is proposed that implies the formation of a peroxo intermediate at the early stages of the reaction. A second intermediate is assumed to be formed at high [H₂O₂]_o which inhibits the progress of the reaction.     

Synthesis of hexamethylene-1,6-dicarbamate by methoxycarbonylation of 1,6-hexamethylene diamine with dimethyl carbonate over bulk and hybrid heteropoly acid catalyst

Synthesis of HDC by methoxycarbonylation of HDA with DMC was carried out over the bulk and hybrid heteropoly acid (HPA) catalyst. The catalysts were systematically characterized by XRD, FTIR, SEM and NH₃-TPD techniques. The by-products produced in the reaction were identified and a possible reaction pathway was proposed based on the by-products analysis. The performances of bulk and hybrid HPA catalysts were evaluated. The H₄[SiW₁₂O₄₀] catalyst revealed high performance compared with other catalysts and its high performance was attributed to its acidic properties. Effects of reaction parameters and reusability of the H₄[SiW₁₂O₄₀] catalyst were also investigated. Under the optimized reaction conditions, HDA conversion reached 93.2% with 64.8% HDC selectivity and only 3.8% by-product selectivity. Moreover, a possible reaction mechanism was proposed for the synthesis of HDC over H₄[SiW₁₂O₄₀] catalyst.     

Stereospecific benzylic dehydroxyfluorination reactions using Bio’s TMS-amine additive approach with challenging substrates

Reactions involving the conversion of a benzylic alcohol into a benzylic fluoride using RSF₃ reagents are notoriously difficult to achieve with high stereochemical inversion (S_N2 reaction) due to competing dissociative S_N1 reaction processes. This Letter develops the methodology of Bio et al., and reports that the addition of a preformed 1:TMS-amine 1:RSF₃ (fluorination reagent) complex as the reagent in these reactions significantly suppresses the S_N1 process and promotes a highly stereospecific reaction generating benzylic fluorination products of high %ee.     

Product-Specific Methods of Syntheses of Hexaphenylcyclotrisiloxane and Octaphenylcyclotetrasiloxane — Monomers of Phenylsilicones

Pure hexaphenylcyclotrisiloxane (P₃) and octaphenylcyclotetrasiloxane (P₄) were synthesized with high yields via proper choice of preparation conditions, such as catalysts, solvents and reaction temperatures, from diphenylsilanediol. Up to 98% yield of this pure starting material can be obtained from diphenyldi-chlorosilane through modifying a known procedure on carefully adjusting the temperature of hydrolysis and washing procedure. This method produced pure P₃ exclusively with high yield (approximately 90%) in ethanol in the presence of concentrated sulfuric acid as the catalyst at various reaction temperatures. P₄ was produced exclusively in high yield (approximately 90%) in alcohols in the presence of sodium hydroxide. A method applying HPLC was used to analyze the reaction products quantitatively.     

Catalytic Decomposition of H2O2over Supported ZnO

Summary.  Transition metal sulfates of Cu(II), Co(II), Ni(II), Cr(III), Mn(II), and Fe(III) supported on ZnO were prepared and characterized by SEM, EDX, and XRD. The kinetics of the heterogeneous decomposition of H₂O₂ over these supported catalysts was investigated. The reaction rate is correlated with both the amount of supported metal ion and its redox potential. The rate of reaction increases with increasing initial concentration of H₂O₂, attains a maximum, and decreases thereafter. It also increases with pH and reaches a maximum at high pH values. A reaction mechanism is proposed that implies the formation of a peroxo intermediate at the early stages of the reaction. A second intermediate is assumed to be formed at high [H₂O₂]_o which inhibits the progress of the reaction. Received April 26, 2000. Accepted (revised) August 24, 2000     

A green and highly efficient alkylation of thiols in water

An environmentally benign and efficient process for the preparation of thioethers was developed by simple and practical reactions of alkyl halides and thiols in water in the presence of K₂CO₃ or Et₃N in very high yields. The reaction of aryl, alkyl, aliphatic and hindered thiols with various alkyl halides gave the corresponding products with significant advantages such as high conversions, short reaction time, mild reaction conditions, and low cost, simple workup with good to quantitative yields.     

The effects of local environment towards yield and selectivity on photocatalytic CO2 reduction catalyzed by metal-organic framework

The CO₂ photoconversion is sensitive to the local reaction environment, of which activity and selectivity can be regulated by the change of reaction systems. This paper focuses on investigating the photocatalytic CO₂ reduction behaviors of MOFs with the involvement of water under different reaction modes, including gas-solid and liquid-solid systems. The CO₂ photoreduction in a liquid-solid system shows high performance in generating HCOOH with the selectivity of 100%. In contrast, the gas-solid system referring to the synergistic interaction of MOFs and H₂O vapor benefits to the formation of gas-phase products, such as CO and CH₄. The possible mechanisms of photocatalytic CO₂ reaction in two modes were investigated by in-situ Fourier-transform infrared spectroscopy, which indicates that the distinction in reaction consequence may result from the difference in CO₂ chemisorbed modes and the proton provision. The choice of reaction system plays an important role in the achievement of high efficiency and selectivity for photocatalytic CO₂ reduction, which is of great practical value in real-world applications.     

A convenient and efficient method for incorporation of pentafluorosulfanyl (SF5) substituents into aliphatic compounds

Both SF₅Cl and SF₅Br undergo smooth, high yield addition to alkenes and alkynes under the mild free radical chain reaction conditions of triethylborane initiation at low temperature, although the SF₅Br chemistry is somewhat limited by its competing high electrophilic reactivity with electron rich alkenes. The SF₅Cl addition reaction is relatively insensitive to a wide variety of non-allylic functionalities.     

Theoretical Study of the Reaction Mechanism and Kinetics of HO2 with XCHO (X = F,Cl)

The reactions of HO₂ with FCHO and ClCHO have been theoretically investigated by combining beyond‐CCSD(T) electronic structure benchmarks, validated density functional theory, and canonical variational transition state theory with small‐curvature tunneling, coupled‐torsions anharmonicity, and high‐frequency anharmonicity. This investigation explores three different reaction mechanisms: radical addition plus a hydrogen transfer, radical addition, and hydrogen abstraction. The calculated results show that the dominant reaction pathway is the terminal oxygen atom of HO₂ added to the carbon atom of XCHO (X = F, Cl) and simultaneously the hydrogen atom of HO₂ transferred to the oxygen atom of the C=O group in XCHO. The reaction barriers of the other reaction pathways are so high that these processes are negligible in the atmosphere. Although the barrier height of the dominant reaction pathway in the HO₂ + FCHO reaction is 0.61 kcal/mol higher than that of the corresponding HO₂ + ClCHO reaction, the HO₂ + FCHO reaction is faster than the HO₂ + ClCHO reaction because the variational effects of HO₂ + ClCHO is more obvious than that of the HO₂ + FCHO. The present results show that the HO₂ + FCHO reaction may be important in the atmosphere. The present results should be useful in evaluating the atmospheric fate of XCHO (X = F, Cl).     

Zirconium oxide (NP) - ionic liquid as an efficient media for the domino Knoevenagel hetero Diels-Alder reaction with unactivated alkynes

Immobilized ZrO₂-nanopowder (NP) in ionic liquid and different organic solvents was used as a suitable Lewis-acid for the synthesis of polycyclic heterocycles which contains pyran-based skeletons. Reaction of O-propargylated salicylaldehyde with active methylene compounds in the presence of ZrO₂-NP in ionic liquid proceeds via domino Knoevenagel hetero Diels-Alder reaction of unactivated alkynes to construct the pyran skeleton. Comparison with different ionic liquids and organic solvents showed that the best results were obtained with 1-butyl-3-methylimidazolium nitrate [bmim][NO₃] because of short reaction times and high yields. Carrying out the reaction under these conditions has advantages such as: high yields, short reaction times and easy work-up.     

Epoxy/poly(4-vinylphenol) blends crosslinked by imidazole initiation

Poly(4-vinylphenol) (PVPh) was used as thermoplastic modifier of epoxy resins. Binary epoxy/PVPh mixtures with high thermoplastic content rise high glass transition temperatures (T _g) after heating, due to the epoxy-phenol reaction. Blends with low PVPh percentages reach high T _g if 2-methylimidazole is added, which catalyses epoxy homopolymerisation and epoxy-phenol reaction. The cured blends do not present phase separation although the network structure depends on the epoxy/phenol ratio. At low PVPh percentage the main crosslinking reaction is epoxy-epoxy but, when the thermoplastic content increases, the epoxy-phenol reaction prevails, causing an important T _g increase and becoming less brittle.     

Regioselective N-nitrosation of dihydropyrimidinones with nitric oxide

N-Nitrosation of dihydropyrimidinones with nitric oxide occurred regioselectively, giving the corresponding N(3)-nitrosamides in high yields. The reaction most likely took place by a nucleophilic attack. Aprotic and polar solvents, such as CH₃CN and tetrahydrofurane (THF) greatly favored the reaction, whereas protic solvents with high dielectric constant, such as CH₃OH and water, disfavored it.     

The synthesis of diene and of vinyl copolymers containing predetermined quantities of polynuclear hydrocarbon or heterocyclic adducts-III. Copolymers formed from polynuclear hydrocarbons and alkyldihalides

The reaction in tetrahydrofuran between the disodium salt of anthracene (A) and alkyl dihalides (RX₂) results in oligomeric products with a repeat unit -[A-R]-. The same reaction with the dilithium derivative is complicated by the high reactivity of this species toward solvent; oligomers with -(CH₂)₄OH end groups are isolated. The xylylene dihalides undergo metallation and Wurtz coupling, and they produce low yields of oligomers rich in xylylene units.The reaction with dilithium acenaphthylene and alkyl dihalides gives a high yield of copolymer but there is evidence of crosslinking. Although addition occurs principally across the 1.2 position, some 1,5 addition is believed to cause this crosslinking. With dilithium phenanthrene the reaction is mainly one of electron transfer; the oligomers produced in low yield are low in phenanthrene adducts.     

Synthesis of benzimidazoles/benzothiazoles by using recyclable,magnetically separable nano-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> in aqueous medium

An efficient, simple, ecofriendly and cost-effective method has been developed for the synthesis of benzimidazole/benzothiazole derivatives by a two-component reaction, involving 1,2-diamino benzene/2-amino thiophenol and substituted aromatic aldehydes using recyclable nano-Fe₂O₃ catalyst (10 mol%) in water afforded with excellent yields (75–85%). The most important feature of this protocol is short reaction times, high yields, aqueous reaction medium, efficient recycling and high stability of the catalyst.     

A highly efficient memantine-modified palladium catalyst for Suzuki–Miyaura cross-coupling reaction

A new simple Pd(memantine)₂Cl₂ complex was synthesized and characterized by ¹H NMR, ¹³C NMR and X-ray single crystal structure determination. The Suzuki–Miyaura reaction of aryl bromides catalyzed by Pd(memantine)₂Cl₂ complex was investigated in air with different temperature. The high turnover numbers of 650,000 have been obtained in the reaction of 4-bromonitrobenzene with phenylboronic acid at 80 °C. At room temperature, the complex also showed high activity for Suzuki–Miyaura cross-coupling reaction of aryl bromides with a wide range of functional groups under air, and the turnover number of up to 99,000 was achieved. The catalytic system also gives good yields toward the reaction of several heteroaryl bromides with thiophenylboronic acid.     

High Resolution Crossed Molecular Beams Study of the H+HD→H2+D Reaction

The H+H₂ reaction is the simplest chemical reaction system and has long been the prototype model in the study of reaction dynamics. Here we report a high resolution experimental investigation of the state-to-state reaction dynamics in the H+HD→H₂+D reaction by using the crossed molecular beams method and velocity map ion imaging technique at the collision energy of 1.17 eV. D atom products in this reaction were probed by the near threshold 1+1'(vacuum ultraviolet+ultraviolet) laser ionization scheme. The ion image with both high angular and energy resolution were acquired. State-to-state differential cross sections was accurately derived. Fast forward scattering oscillations, relating with interference effects in the scattering process, were clearly observed for H₂ products at H₂(v'=0,j'=1) and H₂(v'=0,j'=3) rovibrational levels. This study further demonstrates the importance of measuring high-resolution differential cross sections in the study of state-to-state reaction dynamics in the gas phase.     

Boron-promoted reductive deoxygenation coupling reaction of sulfonyl chlorides for the C(sp3)-S bond construction

Herein, we report a borane-promoted reductive deoxygenation coupling reaction to synthesize sulfides. This reaction features excellent functional group compatibility, high efficiency, broad substrate scope, and application in late-stage functionalization of biomolecules. Preliminary mechanistic studies suggest diaryl sulfides are the intermediates of this reaction. Moreover, the real active aryl sulfide anions may be generated in situ with the aid of B₂pin₂ and react with alkyl tosylates through a concerted S_N2 pathway.     

Mechanism and kinetics of synthesizing dibutoxymethane by phase transfer catalysis

The synthesis of CH₂(OC₄H₉)₂ by phase transfer catalysis (PTC) has been studied in C₆H₅Cl/KOH solution. A pseudo-first-order rate law was applied for describing the reaction at a rather high [KOH]_w. The reaction system was limited by the reaction equilibrium in the aqueous phase at low [KOH]_w and the reaction in the organic phase at high [KOH]_w.     

Synthesis and catalytic application of Pd/PdO/Fe3O4@polymer-like graphene quantum dots

A novel approach was achieved for growing citric acid towards polymer-like graphene quantum dots (PGQD) with high efficiency in the presence of sodium hydroxide as a base catalyst. This protocol is completely safe, simple, fast, and efficient by a bottom up strategy. Thermal treatment of a mixture containing citric acid with NaOH at 300 °C gave PGQD during 5 min. The reaction afforded a new heterogeneous catalyst, Pd/PdO/Fe₃O₄@PGQD, in the presence of Pd and Fe₃O₄. The magnetically recoverable catalyst showed high activity in the oxidation of alkylarenes and alcohols using H₂O₂ as a green oxidant at room temperature. Comparison of the results with previous reports showed the efficiency of the catalyst to have high turnover numbers in mild reaction conditions.