Autoxidation of polystyrene catalyzed by cobalt salt and sodium bromide in chlorobenzene–acetic acid

In the oxidation of atactic polystyrene initiated by azobisisobutyronitrile, the kinetic chain length was obtained as 1.5. In the presence of cobalt salt and bromide ion, the rate of oxidation is first order with respect to the concentration of polymer and second order with respect to the concentration of cobalt. In addition, this rate is dependent on the molar ratio of NaBr to cobalt, independent of the partial pressure of oxygen and the molecular weight of polystyrene. The overall energy of activation is 22.5 kcal/mole. The molecular weight decreased from 152000 to 10 800 under the present conditions of oxidation. Carbon monoxide and carbon dioxide are the only significant volatile products. The primary product of oxidation is hydroperoxide. Benzaldehyde, acetophenone, and phenol were found as final products. The acetophenone-type structure and methyl endgroups were observed. The formation of phenol presented a large selfinhibiting effect in the oxidation of polystyrene. The oxidation of isotactic polystyrene gave a maximum rate of oxidation twofold higher than that of atactic polystyrene and a value of 17.0 kcal/mole for the overall energy of activation.     

Catalyzed liquid-phase oxidation of dialkylthiophenes

The oxidation of 3-methyl-2-ethylthiophene with molecular oxygen in glacial acetic acid in the presence of a cobalt-bromide catalyst was investigated. It was established that there is a dependence of the rate of oxidation of this compound on its concentration, on the catalyst (cobalt acetate) concentration, and on the initiator (NaBr) concentration. The principal oxidation products are 3-methyl-2-acetothienone (III) and 1-(3-methyl-2-thienyl) ethyl acetate, which were isolated and characterized. The reactivity of 3-methyl-2-ethylthiophene in the oxidation reaction is higher than that of 4-methyl-2-ethylthiophene.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 758–761, June, 1981.     

Influence of nanodispersed boehmite on polypropylene photooxidation

Nanocomposites containing pure or organically modified nanoboehmites of different sizes were prepared by melt compounding with polypropylene. The samples were UV light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The presence of pristine nanoboehmites was shown to change the rate of oxidation of polypropylene by reducing the oxidation induction period due to the presence of residual processing antioxidant. The differences of the oxidation induction periods between the nanocomposites and the pristine polymer disappear after solvent extraction of the antioxidant. The inefficiency of traditional antioxidant in retarding the photooxidation of polypropylene containing nanodispersed boehmite is proved. Antioxidant migration to the boehmite surface induced by the preferential interaction with the polar filler is proposed as an explanation. The oxidative behaviour of the organically modified boehmites was shown to depend on the type of organic substituent. p-Toluenesulfonate reduces the adsorption of antioxidants while the presence of a long-chain alkyl benzensulfonate increased the oxidation rate by generation of radical initiators.     

CoFe2O4@SiO2@ Co (III) salen complex nanoparticle as a green and efficient magnetic nanocatalyst for the oxidation of benzyl alcohols by molecular O2

In the presence of cobalt (III) salen complex, selective oxidation of alcohols to carbonyl compounds was studied by molecular oxygen using isobutyraldehyde as an oxygen acceptor. The effect of cobalt (III) salen complex in the oxidation reaction was studied, and the results showed that Co (III) salen complex is very active and selective in the oxidation of various alcohols. Also, the effect of important factors including catalyst amount, solvent and temperature was investigated on the reaction. Furthermore, the catalytic activities of CoFe₂O₄@SiO₂‐supported Schiff base metal complex as well as the effect of molecular oxygen (O₂) as a green oxidant were studied. The results showed that benzaldehyde was the major product and the heterogeneous catalyst was highly reusable.     

Oxidation of styrene epoxide–acid binary system and styrene epoxide–acid–amine ternary system catalyzed by Co(II) salts

The Co(II) salt (nitrate, chloride)-induced acceleration of styrene epoxide (SE) consumption and oxidation by molecular oxygen in acetonitrile solutions of three- and four-component systems, SE–acetic acid–cobalt salt and SE–acetic acid–cobalt salt–aniline, was found and investigated. The heterolytic epoxide ring opening in SE and homolysis (oxidation) catalyzed by cobalt salts can be accomplished in the presence of acid co-catalyst. The competition between homolysis and heterolysis processes in the presence of metal-containing catalyst was discovered for the first time for this type of system. The cobalt catalyst is deactivated during the styrene epoxide conversion.     

Co-APO-5分子筛催化的环己烷选择氧化:溶剂和改性方法对其催化性能的影响

通过合成改性制备了系列Co-APO-5分子筛催化剂,用于环己烷选择氧化,研究了溶剂和改性方法对其催化性能的影响。结果表明,含有π键的极性溶剂对环己烷选择氧化反应有利,环己烷转化率随着π键极性的增加而提高。引入Si和F降低了Co-APO-5分子筛骨架中四配位钴的含量;引入F后Co-APO-5分子筛的结晶度有所提高,而引入Si则能改善Co物种的氧化和还原性,提升其催化反应活性。同时,Co-APO-5的催化活性与其骨架中四配位Co（Ⅱ）的含量相关,说明骨架Co（Ⅱ）是环己烷选择氧化的催化活性中心。     

Oxidation of polyethylene,polypropylene, and copolymers

This investigation of the autoxidation of ethylene–propylene copolymers and polyethylene–polypropylene mixtures was undertaken to determine whether reactivity is a linear function of composition. The copolymers and the mixtures were autoxidized in a trichlorobenzene solution at 100°C in the presence of 1,1′-azodicyclohexanecarbonitrile, and the rates of oxygen absorption were determined. The reactivity of the copolymers and the mixtures, after the underlying absorption of oxygen by initiator radicals is accounted for, is a nearly linear function of composition; however, the polymer mixtures and copolymers oxidized somewhat less readily than predicted by a straight line relationship. Several additional oxidations were performed on solutions of polypropylene so that the effects of initiation rate and substrate concentration could be evaluated. The oxidation kinetics of polypropylene even in dilute solution, are complex; titratable hydroperoxide yields are low. Further work will be required to specify the mechanism of oxidation.     

Influence of stoichiometry and charge state on the structure and reactivity of cobalt oxide clusters with CO

Cationic and anionic cobalt oxide clusters, generated by laser vaporization, were studied using guided-ion-beam mass spectrometry to obtain insight into their structure and reactivity with carbon monoxide. Anionic clusters having the stoichiometries Co2O3(-), Co2O5(-), Co3O5(-) and Co3O6(-) were found to exhibit dominant products corresponding to the transfer of a single oxygen atom to CO, indicating the formation of CO 2. Cationic clusters, in contrast, displayed products resulting from the adsorption of CO onto the cluster accompanied by the loss of either molecular O 2 or cobalt oxide units. In addition, collision induced dissociation experiments were conducted with N 2 and inert xenon gas for the anionic clusters, and xenon gas for the cationic clusters. It was found that cationic clusters fragment preferentially through the loss of molecular O 2 whereas anionic clusters tend to lose both atomic oxygen and cobalt oxide units. To further analyze how stoichiometry and ionic charge state influence the structure of cobalt oxide clusters and their reactivity with CO, first principles theoretical electronic structure studies within the density functional theory framework were performed. The calculations show that the enhanced reactivity of specific anionic cobalt oxides with CO is due to their relatively low atomic oxygen dissociation energy which makes the oxidation of CO energetically favorable. For cationic cobalt oxide clusters, in contrast, the oxygen dissociation energies are calculated to be even lower than for the anionic species. However, in the cationic clusters, oxygen is calculated to bind preferentially in a less activated molecular O 2 form. Furthermore, the CO adsorption energy is calculated to be larger for cationic clusters than for anionic species. Therefore, the experimentally observed displacement of weakly bound O 2 units through the exothermic adsorption of CO onto positively charged cobalt oxides is energetically favorable. Our joint experimental and theoretical findings indicate that positively charged sites in bulk-phase cobalt oxides may serve to bind CO to the catalyst surface and specific negatively charged sites provide the activated oxygen which leads to the formation of CO 2. These results provide molecular level insight into how size, stoichiometry, and ionic charge state influence the oxidation of CO in the presence of cobalt oxides, an important reaction for environmental pollution abatement.     

Influence of nanodispersed hydrotalcite on polypropylene photooxidation

Nanocomposites containing hydrotalcite and prepared by melt compounding with polypropylene were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies.The presence of hydrotalcite was shown to change the global rate of photooxidation of polypropylene by reducing the oxidation induction time and increasing the oxidation rate. The differences of the oxidation induction time disappeared after solvent extraction of the antioxidant. They were attributed to a quenching of the antioxidant activity resulting from a migration onto the filler surface induced by the preferential interaction with the polar hydrotalcite. Extracting the antioxidant did not change the oxidation rate at the permanent regime. The increase of the oxidation rate was attributed to transition metal ions, present as impurities in hydrotalcite, which can accelerate the oxidation of the polymer by various mechanisms including a catalysed decomposition of hydroperoxides.     

Low-Temperature Oxidation of Cobalt Nanoparticles with Water Vapor

The oxidation of Co nanoparticles with water vapor and molecular oxygen was studied over the temperature range 10–200°C. Cobalt particles reacted with water vapor at p _{H 2}O = 18 torr. Preadsorbed hydrogen and CO had no pronounced influence on the oxidation rate of cobalt nanoparticles. Temperature-programmed reduction showed that, after the oxidation of cobalt nanoparticles with water vapor, oxidized cobalt was in the divalent state.     

Kinetics and products of the catalytic oxidation of acetamidotoluenes with ozone in acetic acid

The kinetics of acetamidotoluene oxidation in glacial acetic acid in the presence of cobalt acetate is reported. At 95°C and atmospheric pressure, acetamidotoluenes are oxidized by molecular oxygen very slowly: oxidation is complete in 10–12 h, and the major reaction products are acetamidobenzoic acids (27–36% yield). The introduction of ozone into the reactive gas increases the reaction rate by one order of magnitude. The main role of ozone is to generate the active form of the catalyst.     

Allylation and oxidation reactions promoted by cobalt(II) complexes

Two examples of radical reactions involving cobalt complexes are described. The first one concerns the reactions of allylcobaloximes with 2-bromo 2-phenylacetonitriles leading to the corresponding monoallyl derivatives. It is shown that both the rate and regioselectivity of the reactions are affected by the nature of the substituents on the phenyl group: electron-withdrawing groups give higher rates and highly regiospecific reactions. The second type of radical reaction which finds useful synthetic applications is the oxidation of phenols by 02 catalyzed by Schiff base cobalt complexes. By choosing carefully the catalyst and the solvent, these oxidations can be highly selective, quinones being the major oxidation products in most cases.     

Solvent sorption effects on the structure and properties of PP/Rodrun blends

Toluene, carbon tetrachloride, and tetrahydrofuran sorption and desorption by polypropylene (PP) and PP/thermotropic liquid crystal polymer (Rodrun) blends with 20 and 40% Rodrun contents were studied as well as the effects of the solvent presence on the structure and mechanical properties. The rate of sorption and desorption and the solvent content at the equilibrium were higher in the blends than in pure PP. This was attributed to microcracking in the PP matrix induced by the presence of Rodrun. Taking into account the very low permeability of Rodrun to the solvents of this work, and the increase in specific volume of the blends as a result of sorption, sorption‐induced additional microcracking, partially in the form of debonding of the dispersed Rodrun phase, is also believed to occur. Plasticization was the main effect on mechanical properties. The partially irreversible effect of sorption on the mechanical properties agrees with the proposed partial debonding and weak solvent resistance of these blends. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1090–1100, 2000     

Mild Oxidation of Cyclohexane Catalyzed by Cobalt(II) Acetate and Initiated by H2O2 in the Acetic Acid Medium

The homogeneous catalytic oxidation of cyclohexane by molecular oxygen and hydrogen peroxide in a solution of acetic acid (HOAc) in the presence of cobalt(II) acetate Co(OAc)₂ is studied. The high yields of cyclohexanol, cyclohexanone, and cyclohexyl hydroperoxide (0.10–0.15 mol/l) and the high rate of the process (w = 10^–5–10^–4 mol l^–1 s^–1) are explained by (1) mild conditions of oxidation in the medium of the HOAc solvent and (2) efficient initiation of the process due to the fast kinetics-controlled dissociation of H₂O₂ into radicals in the studied reaction medium under the action of cobalt cations. Quantitative relationships are found for the cyclohexane oxidation rate, the yield of target products, and the ratio of reactants participating in the process. The effect of hydrogen hydroperoxide additives on the concentrations of reduced and oxidized forms of the catalyst is studied by spectrophotometry in model mixtures. Quantum chemistry is employed to calculate the probabilities of some key elementary reactions. Calculated data agree well with the experiment.     

Oxidation of α-pinene by atmospheric oxygen in the supercritical CO<Subscript>2</Subscript>—ethyl acetate system in the presence of Co(II) complexes

The reactivity of monoterpene α-pinene in a flow reactor in the presence of cobalt catalyst in a complex supercritical solvent consisting of CO₂ and ethyl acetate is studied over the temperature range of 190–320°C and a pressure range of 110–125 atm. It was found that the main isomerization products include compounds with bicyclo[2.2.1]heptane and p-menthane backbones; the reaction is accompanied by partial racemization. The formation of oxidation products is observed in the presence of air, with epoxydation rather than allylic oxidation being the predominant process at the first stage. The oxidized products (campholenic aldehyde, verbenone, pinocamphone) are shown to be formed with a high enantioselectivity; the formation of acetoxylation products is observed at temperatures above 200°C.     

Liquid-phase catalytic oxidation of 2-methoxymethylthiophene

The oxidation of 2-methoxymethylthiophene with molecular oxygen in the presence of a cobalt bromide catalyst in the kinetic region at 65–100 °C was investigated. It is shown that the principal products are 2-formylthiophene and methylthiophene-2-carboxylate in a ratio of 12. The composition of the products does not depend on the oxidation temperature and changes as the starting concentration of 2-methoxymethylthiophene and the amount of cobalt bromide catalyst are changed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 924–928, July, 1980.     

Co@Pt–Ru core-shell nanoparticles supported on multiwalled carbon nanotube for methanol oxidation

A novel synthesis route concerning reduction of cobalt core onto the surface of multiwalled carbon nanotubes (MWCNTs) and then substitution of part of Co core with Pt–Ru precursor was developed to synthesize the core-shell Co@Pt–Ru/MWCNTs catalyst. In this synthesis route, sodium borohydride and hydrazine hydrate were employed to reduce cobalt step by step in order to control the size of cobalt and the growth speed of cobalt crystal. The novel core-shell Co@Pt–Ru/MWCNTs catalyst shows good electrocatalysis towards methanol oxidation.     

Formation and dissociation equilibria of intermediate species in the oxidation of cobalt(II)-dipeptide complexes

Summary The oxidation of various cobalt(II)-dipeptide complexes in the presence of both molecular oxygen and hydrogen peroxide is examined. The nature of the oxidant exercises a marked influence on the reaction path. The oxo-intermediate species formed apparently possesses different structures, depending on the oxidant. Moreover, when molecular oxygen is employed, the inertness of the resulting cobalt(III)-dipeptide complexes is much higher, suggesting a different degree of protonation. The effect of the ligand structure on the oxidative process is considered; the reaction rate is found to be strongly influenced by the hydrophobicity of the substituent group and by the presence of amidic hydrogen.     

Alkene hydrogenation over palladium supported on a carbon–silica material

Palladium catalysts supported on a carbon–silica material were synthesized. Hydrogenation by molecular hydrogen was studied in the presence of straight-chain and cyclic olefins. As distinct from what is observed for olefins having a phenyl substituent, for aliphatic alkenes the reaction rate decreases with an increasing conversion due to the accumulation of hydrogenation products. The synthesized palladium catalysts show a higher hydrogenation activity than Pd/C.     

Synthesis of Nanoporous Carbon–Cobalt‐Oxide Hybrid Electrocatalysts by Thermal Conversion of Metal–Organic Frameworks

Nanoporous carbon–cobalt‐oxide hybrid materials are prepared by a simple, two‐step, thermal conversion of a cobalt‐based metal–organic framework (zeolitic imidazolate framework‐9, ZIF‐9). ZIF‐9 is carbonized in an inert atmosphere to form nanoporous carbon–metallic‐cobalt materials, followed by the subsequent thermal oxidation in air, yielding nanoporous carbon–cobalt‐oxide hybrids. The resulting hybrid materials are evaluated as electrocatalysts for the oxygen‐reduction reaction (ORR) and the oxygen‐evolution reaction (OER) in a KOH electrolyte solution. The hybrid materials exhibit similar catalytic activity in the ORR to the benchmark, commercial, Pt/carbon black catalyst, and show better catalytic activity for the OER than the Pt‐based catalyst.