Study of homo- and cross-coupling competition in the reaction of triarylbismuth(V) dicarboxylates with methyl acrylate in the presence of a palladium catalyst

Triarylbismuth(V) derivatives Ar₃Bi(O₂CR)₂ (Ar = Ph, m-Tol, p-Tol; R = H, Me, Et, n-Bu, t-Bu, n-C₅H₁₁, CF₃, CH₂Cl, CCl₃, Ph) were prepared in good to excellent yields by reaction of Ar₃Bi with equimolar amounts of t-BuOOH in the presence of an acid. These compounds were tested in the C-arylation reaction of methyl acrylate, as a model substrate, in the presence of palladium catalyst (4 mol%). It was found that triphenylbismuth dicarboxylates are very active phenylating agents under mild conditions (20 °C). The effect of the carboxylic group, the effect of the nature of the palladium catalyst and the effect of oxygen on the reactivity of the organobismuth compounds and on the selectivity of the C-arylation reaction were studied. Methyl cinnamate, the C-phenylation product, and biphenyl, the homo-coupling by-product, were obtained in all cases. Triphenylbismuth divalerate Ph₃Bi(O₂CBu)₂ is the most reactive compound among the triphenylbismuth dicarboxylates studied.     

Catalytic C-phenylation of methyl acrylate with tetraphenylantimony(v) halides and carboxylates

Catalytic C-phenylation of methyl acrylate to methyl cinnamate with the Ph₄SbX complexes (X = F, Cl, Br, OH, OAc, O₂CEt) in the presence of the palladium compounds PdCl₂, Pd(OAc)₂, Pd₂(dba)₃, Pd(Ph₃P)₂Cl₂, and Pd(dppf)Cl₂ (dba is dibenzylideneacetone and dppf is bis(diphenylphosphinoferrocene)) was studied in organic solvents (MeCN, THF, DMF, MeOH, and AcOH). The highest yield of methyl cinnamate (73% based on the starting organometallic compound) was obtained for the Ph₄SbCl—PdCl₂ (1 : 0.04) system in acetonitrile.     

Gold and platinum catalyzed cascade reaction of propargyl acetates bearing terminal alkynes or methyl ketones

A gold (III)-catalyzed cascade reaction of propargyl acetates bearing an extra terminal alkyne (1) afforded γ-keto esters 3 and lactones 4. These products should be generated through allenyl ketone intermediate B via a 1,2-acyloxy cyclization/fragmentation/cycloisomerization/hydrolysis sequence. On the other hand, the cascade reaction of α-acetoxy ketones bearing terminal alkynes 5 afforded lactone 6 via allenyl ketone intermediate A. This reaction involves a [3,3]-sigmatropic acyloxy rearrangement/cycloisomerization/hydrolysis sequence.     

Adsorption of antimony(III) and antimony(V) on bentonite: Kinetics, thermodynamics and anion competition

This research attempted to study the adsorption of Sb(III) and Sb(V) on bentonite using batch experiments. The effects of reaction time, temperature, initial Sb concentration, and competitive anions at different concentrations on the adsorption of Sb(III) and Sb(V) were investigated. Kinetic studies suggested that the adsorption equilibriums for both Sb(III) and Sb(V) were reached within 24 h. The desorption of Sb adsorbate on the bentonite was observed following Sb(III) adsorption, probably due to the oxidation of Sb(III) on the bentonite surface and subsequent desorption of Sb(V). In addition, oxidation of Sb(III) can occur in the solution medium also, which decreases the concentration of Sb(III) in the solution thereby driving the equilibrium in the direction of desorption from the surface. The adsorption data at three temperatures were successfully modeled using Langmuir (r² > 0.82) and Freundlich (r² > 0.99) isotherms. The thermodynamic parameters (ΔG⁰, ΔH⁰, and ΔS⁰) were calculated from the temperature dependence, suggesting that the adsorption process of Sb(III) is spontaneously exothermic, while the adsorption process of Sb(V) is spontaneously endothermic. Competitive anions such as , , and hardly affected the Sb(III) adsorption on bentonite, while and could compete with for adsorption sites. The competition between and on adsorption sites was presumably due to the formation of surface complexes and the surface accumulation or precipitation of on bentonite surface.     

Arylations mediated by lead(IV) in the presence of formazan and imine ligands

The use of formazan and imine ligands in arylations of β-dicarbonyl systems by phenyl boronic acid/lead(IV) carboxylates is examined.     

Sub-Microdetermination of Antimony (Iii) and Antimony (V) In Natural and Polluted Waters and Total Antimony In Biological Materials By Flameless Aas Following Extractive Separation With N-P-Methoxyphenyl-2-Furylacrylohydroxamic Acid

Abstract

Antimony (III) was separated from antimony (V) by extractive separation from 2–10^?6 M HC1 media with N-p-methoxyphenyl-2-furylacrylohydroxamic acid (MFHA) in chloroform and determined by graphite furnace atomic absorption spectroscopy at 2600°C using copper as matrix modifier. Antimony (V) was subsequently reduced to the trivalent form with acidic (-1M HC1) potassium iodide solution and determined as above. the mutual tolerance between antimony (III) and antimony (V) in the present mothod was very high-either of the species could be determined in presence of 15 times higher concentration of the other species. the sepatation-AAS determination system enabled accurate differential analysis of the metalloid in natural/ polluted waters down to 10^?2 ppb (ug 1^?1) levels. the method was also applied to the analysis of antimony in vehicle exhaust particulates, plant tissues, and animal tissues. the method was validated by analysing several certified reference materials with and without standard addition of antimony. MFHA was chosen from amongst thirteen new hydroxamic acids.     

Development of an unexpected reaction pathway for the synthesis of 1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines through palladium-catalyzed cascade reactions

1,2,4-trisubstituted pyrrolo[1,2-a]quinoxalines are synthesized through the multi-component reaction of 3-substituted 2-chloroquinoxalines, propargyl bromide, and excess secondary amines in the presence of a palladium copper catalytic system. This one-pot process provides an unexpected synthesis of new trisubstituted pyrrolo[1,2-a]quinoxalines by the introduction of two amine substituents onto the fused pyrrole rings in a single reaction procedure. The compounds formed are fully characterized by the analytical spectral data and X-ray analysis. A number of synthesized pyrrolo[1,2-a]quinoxaline derivatives are also screened against the three bacterial strains Micrococcus luteus, Pseudomonas aeruginos, and Bacillus subtilis. According to the results obtained, compounds 3b, 3c, and 3e are active against M. luteus, compounds 3b and 3e are active against Ps. Aeruginos, and only compound 3f is active against all the three bacterial strains.     

SET‐LRP of methyl acrylate catalyzed with activated Cu(0) wire in methanol in the presence of air

Single electron transfer‐living radical polymerization (SET‐LRP) of methyl acrylate (MA) in methanol, catalyzed with nonactivated and activated Cu(0) wires, was performed in the presence of nondeoxygenated reagents and was investigated under a simple blanket of nitrogen. The addition of a small amount of hydrazine hydrate mediates the deoxygenation of the reaction mixture by the consumption of oxygen through its use to oxidize Cu(0) to Cu₂O, followed by the reduction of Cu₂O with hydrazine back to the active Cu(0) catalyst. SET‐LRP of MA in methanol in the presence of air requires a smaller dimension of Cu(0) wire, compared to the nonactivated Cu(0) wire counterpart. Activation of Cu(0) wire allowed the polymerization in air to proceed with no induction period, linear first‐order kinetics, linear correlation between the molecular weight evolution with conversion, and narrow molecular weight distribution. The retention of chain‐end functionality of α,ω‐di(bromo) poly(methyl acrylate) (PMA) prepared by SET‐LRP was demonstrated by a combination of experiments including ¹H NMR spectroscopy and matrix‐assisted laser desorption ionization–time of flight mass spectrometry after thioetherification of α,ω‐di(bromo) PMA with thiophenol. In SET‐LRP of MA in the presence of limited air, bimolecular termination is observed only above 85% conversion. However, for bifunctional initiators, the small amount of bimolecular termination observed at high conversion maintains a perfectly bifunctional polymer. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Spectrophotometric determination of hydrogen peroxide in rainwater

Hydrogen peroxide in rainwater has been determined from the measurement of absorption at 432 nm after the formation of the stable oxo-peroxo-pyridine-2,6-dicarboxylatovanadate(V) complex (OPDV) in acid media. Determinations were in good agreement with those using a modified p-hydroxyphenylacetic acid (PHPA) emission method. The linear range for the OPDV method is from 0.05 to 50 ppm H₂O₂, and the limit of detection under the analytical conditions employed was 5.8 nmol H₂O₂ for a 20 cm³ rainwater sample. The volume weighted mean H₂O₂ concentration in rainwater collected at roof-top level in central Kowloon was 15.9 μM (N=10), and the ratio of non-sea salt sulphate and H₂O₂ concentrations was significantly correlated with pH. The OPDV absorption method was also employed for the determination of ambient gaseous H₂O₂, and liquid-nitrogen cold-trap collection gave results about 30% lower than impinger sampling, where artifact H₂O₂ formation occurred.     

Tail-to-tail dimerization of methyl acrylate in the presence of triphenylarsine ruthenium complexes

Catalytic dimerization of methyl acrylate by homogenous ruthenium catalysts was investigated. The effect of the addition of acidic additives, supporting ligands, polymerization inhibitor, and reaction conditions on the selectivity of dimerization was studied, and possible reaction mechanism was discussed. Conversion and selectivity were significantly affected by using triphenylarsine as supporting ligand. Under mild conditions, conversion up to 98% with good selectivity to tail-to-tail product was achieved.     

Elimination of β-palladium hydroxide in the Pd-catalyzed reaction of methyl (α-hydroxymethyl)acrylate with alcohols

Exclusive elimination of β-Pd-OH takes place in the oxypalladation intermediate derived from methyl (α-hydroxymethyl)acrylate and alcohols with PdCl₂ catalyst, and no β-Pd-H elimination occurs.     

Stabilization and kinetics in the emulsion copolymerization of butyl acrylate and methyl methacrylate

We carried out emulsion homopolymerizations and copolymerizations of butyl acrylate (BuA) and methyl methacrylate (MMA) with different types and concentrations of surfactants to determine the influence of these parameters on the particle size and particle size distribution and to elucidate the mechanism of particle formation. As expected, the mechanisms of nucleation above and below the critical micelle concentration were very different; however, it was also found that the presence of partially soluble monomers such as MMA in the water phase had a significant influence on the critical micelle concentration of Triton X‐405 (>50%). In addition, the nucleation mechanism during copolymerization seemed to be dominated by BuA, with the number of particles per liter being very similar to the number nucleated during its homopolymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2832–2846, 2001     

Degradation of vinylidene chloride/methyl acrylate copolymers in the presence of metal formates

Vinylidene chloride copolymers have a number of superior properties, most notably, a high barrier to the transport of oxygen and other small molecules. As a consequence, these materials have assumed a position of prominence in the packaging industry. At processing temperatures these copolymers tend to undergo degradative dehydrochlorination. The dehydrochlorination reaction is a typical chain process with distinct initiation, propagation, and termination phases. It has been demonstrated that initiation of degradation is strongly facilitated by the presence of unsaturation along the backbone. Such unsaturation may be introduced via interaction of the polymer with a variety of agents which might commonly be encountered during polymerization or processing. The presence of an unsaturated unit within the polymer generates an allylic dichloromethylene which may function as a major defect (labile) site for the initiation of degradation. The conversion of these dichloromethylene units into non-reactive groups would interrupt propagation of the dehydrochlorination reaction and lead to the stabilization of the copolymer. Potential stabilization in the presence of metal formates has been examined using a vinylidene chloride/methyl acrylate (five mole percent) copolymer and thermogravimetric techniques. The effect of the metal formate on the stability of the polymer reflects the relative halogenophilicity of the metal cation present. Metal formates (sodium, calcium, nickel(II) and to a lesser extent lead(II), cadmium, manganese(II) and magnesium) may be expected to be ineffective as stabilizers for vinylidene chloride copolymers. At the other extreme, metal formates which contain cations sufficiently acidic to actively strip chlorine from the polymer backbone, e.g., zinc formate, will function to enhance the degradation process. An effective carboxylate stabilizer must contain a metal cation sufficiently acidic to interact with allylic chlorine and to facilitate its displacement by the carboxylate anion. Copper(II) formate may possess the balance of cation acidity and carboxylate activity to function as an effective stabilizer for vinylidene chloride copolymers.     

Telomerization of aceylonitkile and methyl acrylate with bromotrichloromethane in the presence of iron pentacarbonyl

Conclusions Initiating systems that contain iron pentacarbonyl and a cocatalyst (iodine, dimethylaniline) make it possible to run the telomerization of acrylonitrile and methyl acrylate with bromotrichloromethane under mild conditions, with a total yield of 55–65% of the first two telomer homologs.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 181–184, January, 1973.     

Poly(ascorbyl acrylate)s: Synthesis and evaluation of their redox polymerization ability in the presence of hydrogen peroxide

In this work, a strategy for chemical synthesis of ascorbic acid functionalized polyacrylates (PAAA) was accomplished in a two‐step process, first a reversible addition fragmentation chain‐transfer (RAFT) polymerization on a benzyl‐protected ascorbyl acrylate monomer, followed by a deprotection (debenzylation) reaction. The polymers were characterized by ¹H NMR, ¹³C NMR and gel permeation chromatograph. The polymerization ability of redox pair including PAAA and H₂O₂ were conducted through the measurement of 2‐hydroxyethyl acrylate (HEA) conversion against time via real‐time FT‐NIR. It was found that PAAA in the presence of H₂O₂, independent on itself chain length, exhibited much faster polymerization than small molecule ascorbic acid (smAA) as reductant at identical condition. Interestingly, when the concentration of ascorbate repeating unit was over some critical value, the polymerization kinetics of HEA could be tunable by simply adjusting the initial molar ratio of reductant to oxidant and environmental pH. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Oxidation of methyl phenyl sulfide by carbamide peroxide in the presence of activators

The oxidation of methyl phenyl sulfide by carbamide peroxide in water and water–ethanol mixtures proceeds at the same rates as oxidation by hydrogen peroxide. In the presence of ammonium bicarbonate, the reaction proceeds through a pathway including HCO₄^- as a more active oxidizing agent than H₂O₂.     

Reaction of methyl acrylate with N,N-dimethylethanolamine in the presence of a titanium alkoxide

The kinetic features were examined for transesterifi cation of methyl acrylate with N,N-dimethylethanolamine in the presence of tetra(N,N-dimethylaminoethyl) titanate at different molar ratios of the reactants and at temperatures within 50?C80°C, as well as for side reactions of Michael addition at 95?C125°C. The major parameters governing the selectivity of the synthesis of N,N-dimethylaminoethyl acrylate were determined.     

Kinetics and hazards of thermal decomposition of methyl ethyl ketone peroxide by DSC

Differential scanning calorimetry (DSC) was applied to analyze thermal decomposition of methyl ethyl ketone peroxide (MEKPO). Thermokinetic parameters and thermal stability were evaluated. MEKPO decomposes in at least three exothermic decomposition reactions and begins to decompose at 30–32 °C. The total heat of decomposition is 1.26 ± 0.03 kJ g⁻¹. Thermal decomposition of MEKPO can be described by a model of two independent reactions: the first is decomposition of a less stable isomer of MEKPO, followed by decomposition of the main isomer, after which an exothermic reaction of the reaction products with the solvent, dimethyl phthalate. The results can be applied for emergency relief system design and for emergency rescue strategies during an upset or accident.     

Kinetics of the reaction of 2,6-si-t-butylphenol with methyl acrylate in the presence of potassium 2,6-di-t-butylphenolate and the effect of proton-donor components on the mechanism of this reaction

A kinetic scheme is proposed for the reaction of 2,6-di-t-butylphenol with methyl acrylate in the presence of potassium 2,6-di-t-butylphenolate. Rate constants have been calculated for the elementary stages which describe the mechanism of catalysis and the effect on the kinetic laws of the protondonor components 2,6-di-t-butylphenol, water, and methanol. The kinetic scheme contains 30 components and includes 62 rate constants for the elementary stages, which were calculated by mathematical modeling of the kinetics of the process. The calculated results are compared with experimental data for the dependence of the rate of consumption of 2,6-di-t-butylphenol on the concentration of potassium 2,6-di-t-butylphenolate and on the concentrations of the proton-donor components.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 989–996, May, 1991.     

Determination of Sb(V) Using Differential Pulse Anodic Stripping Voltammetry at an Unmodified Edge Plane Pyrolytic Graphite Electrode

Antimony(V) determination at an unmodified edge plane pyrolytic graphite (EPPG) electrode using anodic stripping voltammetry (ASV) by depositing beyond the hydrogen wave is shown in this paper. By depositing beyond the hydrogen wave, we report a sensitive method to determine pentavalent antimony at a carbon electrode in 0.25 M HCl. Using differential pulse anodic stripping voltammetry (DPASV), a bare EPPG electrode gave a detection limit of 5.8±0.02 nM without the need for surface modification. This level is greatly within the EU limit for drinking water of 40 nM.