Catalytic epoxidation of polyisobutylene-co-isoprene with hydrogen peroxide

Polyisobutylene-co-isoprene (PIBI) can be epoxidized with hydrogen peroxide in the presence of methyltrioctylammonium tetrakis (diperoxotungsto) phosphate(3-) as the catalyst in a biphasic system. The effects of the reaction time and temperature, the ratio of the organic phase to the aqueous phase, the concentration of the catalyst and polymer and stirring intensity, respectively, are studied on the conversion of double bonds to oxirane groups. ¹H-NMR analysis confirms the absence of ring opening side reactions in this epoxidation reaction system. The kinetics of the reaction are discussed. The rate constants are measured at four temperatures and the activation energy for the reaction is determined as 54.2kJ/mol. The optimum reaction temperature is about 60°C.     

Expedient Method for Oxidation of Alcohol by Hydrogen Peroxide in the Presence of Amberlite IRA 400 Resin (Basic) as Phase‐Transfer Catalyst

Amberlite IRA 400 (strongly basic), a classical polymer imparts phase‐transfer catalysis in the oxidation of primary and secondary alcohols by hydrogen peroxide to give excellent yields of the corresponding carbonyl compounds or carboxylic acids in acetonitrile solvent at reflux temperature in 4–6 h. The catalytic system is inert to other susceptible oxidation sites such as carbon–carbon double bonds     

Co-MCM-41催化H2O2氧化4-甲基吡啶生成4-吡啶甲酸的反应条件及机理

研究了乙酸溶剂中无引发剂条件下,Co掺杂MCM-41催化过氧化氢（30%）氧化4-甲基吡啶的反应,催化剂表现出高底物转化率和产物吡啶甲酸选择性以及良好的再生性。 探讨了不同溶剂、反应时间、反应温度、催化剂用量等对H2O2氧化4-甲基吡啶反应的影响,确定较优反应条件为m（4-甲基吡啶)∶m（催化剂)=10∶1,V（4-甲基吡啶)∶V（冰醋酸)=1∶10,温度363 K,时间6 h。 该条件下4-甲基吡啶的转化率为96.5%,4-吡啶甲酸的选择性为91.4%。 探讨了可能的反应机理。     

Heterogeneous Baeyer-Villiger oxidation of ketones with H2O2/nitrile, using Mg/Al hydrotalcite as catalyst

We synthesized a magnesium-aluminium hydrotalcite and used it as a catalyst in the Baeyer-Villiger (BV) oxidation of cyclohexanone with a mixture of 30% aqueous hydrogen peroxide and benzonitrile as oxidant. The hydrotalcite proved an excellent catalyst for the process. The influence of experimental variables was examined in depth in order to bring the working conditions as close as possible to those usable on an industrial scale. We optimized the cyclohexanone/hydrogen peroxide/benzonitrile proportion and used various nitriles, solvents and amounts of catalyst, benzonitrile and methanol proving the most effective nitrile and solvent, respectively, for the intended purpose. The reaction was found to occur to an acceptable extent with other carbonyl compounds as substrates; by exception, α,β-unsaturated carbonyl compounds provided poor results by effect of their undergoing competitive epoxidation of their double bonds.     

A spectroscopic study on the reaction-controlled phase transfer catalyst in the epoxidation of cyclohexene

The epoxidation of cyclohexene with hydrogen peroxide in a biphase medium (H₂O/CHCl₃) was carried out with the reaction-controlled phase transfer catalyst composed of quaternary ammonium heteropolyoxotungstates [π-C₅H₅N(CH₂)₁₅CH₃]₃[PW₄O₁₆]. A conversion of about 90% and a selectivity of over 90% were obtained for epoxidation of cyclohexene on the catalyst. The fresh catalyst, the catalyst under reaction conditions and the used catalysts were characterized by FT-IR, Raman and ³¹P NMR spectroscopy. It appears that the insoluble catalyst could degrade into smaller species, [(PO₄){WO(O₂)₂}₄]³⁻, [(PO₄){WO(O₂)₂}₂{WO(O₂)₂(H₂O)}]³⁻, and [(PO₃(OH)){WO(O₂)₂}₂]²⁻ after the reaction with hydrogen peroxide and becomes soluble in the CHCl₃ solvent. The active oxygen in the [W₂O₂(O₂)₄] structure unit of these soluble species reacts with olefins to form the epoxides and consequently the corresponding W---Ob---W (corner-sharing) and W---Oc---W (edge-sharing) bonds are formed. The peroxo group [W₂O₂(O₂)₄] can be regenerated when the W---Ob---W and W---Oc---W bonds react with hydrogen peroxide again. These soluble species lose active oxygen and then polymerize into larger compounds with the W---Ob---W and W---Oc---W bonds and then precipitate from the reaction solution after the hydrogen peroxide is consumed up. Part of the used catalyst seems to form more stable compounds with Keggin structure under the reaction conditions.     

Studies on the atom transfer radical polymerization of a maleimide AB* monomer and modification of the halogen end groups

The atom transfer radical polymerization (ATRP) of an AB* monomer, N-(4-α-bromobutyryloxy phenyl)maleimide (BBPMI), was conducted using the complex of CuBr/2,2′-bipyridine as catalyst. The study of kinetics of polymerization and the growth behavior of macromolecules show that the polymerization proceeds rapidly in first 1 h and then slows down. The decrease in the rate of polymerization is ascribed to the poor reactivity of maleimide radicals from A* to initiate the polymerization of maleimide double bonds. The molecular weight of the resulting polymer also increases with the dosage of catalyst. The coincidence of molecular weight determined by hydrogen proton nuclear magnetic resonance spectroscopy (¹H NMR) and gel permeation chromatography (GPC) proves that the resulting polymer is of linear structure, which is further verified by ¹³C NMR measurement and high performance liquid chromatography (HPLC) analysis of the hydrolysate of the resulting polymer. The stabilization modification of the halogen end groups of the resulting polymer by free-radical chain transfer reaction was attempted under ATRP condition. Isopropyl benzene was employed as the chain transfer agent. Indeed, the modified polymer with carbon-bromine bonds conversion of 40.7% shows enhanced thermal stability. The initial weight loss temperature has been increased from 193 to 243 °C. On the other hand, the atom transfer radical copolymerization of BBPMI with styrene resulted in the formation of hyperbranched polymer.     

The Formation of Terminal Double Bonds in Vinyl Chloride Polymerization

The determination of double bonds in PVC is achieved with an increased accuracy in comparison with earlier methods by the addition of iodine monochloride (Wijs reaction) to PVC coupled with x-ray fluorescence analysis to determine the iodine content of the polymer. The number of double bonds per unit weight of polymer increases on increasing the polymerization temperature and is proportional to the number of polymer molecules. It is not affected, however, by the presence of the chain transfer agent tetrahydrofuran (THF). At the technically important polymerization temperatures of 30 to 80°C and in the absence of the chain transfer agent, 0.9 double bonds per polymer molecule are found. The number of double bonds per polymer molecule is lowered using the chain transfer agent THF. These results support the theory that the chain transfer to monomer and possibly the termination reaction are coupled with the formation of terminal double bonds. Contributions by internal double bonds formed by dehydrochlorination of the polymer during polymerization are excluded by investigating the Cl^θ content of the water phase in the oxygen-free VC suspension polymerization. No hydrogen chloride is formed. In IR spectra of PVC, the stretching vibration of the double bonds is detected at 1667 cm^?1 by the correlation of the double bond contents and the intensities of the absorption bands. The stretching vibration at 1667 cm^?1is in accordance with those of model compounds with a 1-chloro-2-alkene structure.     

反应控制相转移催化环氧化苯乙烯

研究了磷钨杂多酸盐反应控制相转移催化H2O2直接氧化苯乙烯制环氧苯乙烷的反应,考察了溶剂、H₂O₂用量、催化剂用量、反应温度、时间、苯乙烯浓度等因素对反应的影响。 获得的适宜的反应条件为：乙酸乙酯为溶剂,n(苯乙烯)∶n(H₂O₂)∶n(催化剂)=300∶300∶1,反应温度60 ℃,反应时间6 h,反应液中苯乙烯质量分数为10%。 在该条件下,苯乙烯的转化率为85.5%,环氧苯乙烷的选择性为84.9%。 催化剂可过滤回收,循环使用2次后的活性无明显下降。     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Selective oxidation of aromatic primary alcohols to aldehydes using molybdenum acetylide oxo-peroxo complex as catalyst

Selective oxidation of various aromatic alcohols to aldehydes has been carried out with very high conversion (90%) and selectivity (90%) for aldehydes using cyclopentadienyl molybdenum acetylide complex, CpMo(CO)₃(CCPh) (1) as catalyst and hydrogen peroxide as environmentally benign oxidant. Water-soluble Mo acetylide oxo-peroxo species is formed in situ after reaction of 1 with aqueous hydrogen peroxide during the course of reaction as catalytically active species. Interestingly even though the catalyst is homogeneous it could be recycled very easily by separating the products in organic phase and catalyst in aqueous phase using separating funnel. Even after five recycles no appreciable loss in alcohol conversion and aldehyde selectivity was observed.     

钨过氧酸盐离子液体催化过氧化氢氧化苯甲醇制苯甲酸

用甲基三辛基氯化铵和钨酸钠一步法合成甲基三辛基季铵钨酸盐离子液体[(CH3)N(n-C8H17)3]2W2O11,以该离子液体为催化剂,在无反应溶剂条件下催化过氧化氢氧化苯甲醇生成苯甲酸。 考察了反应温度、催化剂用量以及氧化剂过氧化氢用量对苯甲酸产率的影响。 确定优化条件：反应温度70 ℃,苯甲醇用量5 mmol,催化剂用量是底物的0.4%(摩尔分数),30%过氧化氢用量2 mL,苯甲醇的转化率可达99%,苯甲酸选择性为98%。 该方法具有反应条件温和、产率高和选择性好的优点。     

Carvone epoxidation by system “hydrogen peroxide-[Mn2L2O3][PF6]2 (L = 1,4,7-trimethyl-1,4,7-triazacyclononane)-carboxylic acid”: a combinatorial approach to the process optimization?

Summary Epoxidation of natural terpene (+)-carvone by the system consisting of a catalyst, oxalic acid (co-catalyst) and H₂O₂ (70% aqueous solution; oxidant) was studied and factorial design methods were applied for the optimization of this reaction. A dinuclear manganese(IV) complex [LMn(O)₃MnL](PF₆)₂ (L = 1,4,7-trimethyl-1,4,7-triazacyclononane) was used as a catalyst, and acetonitrile was employed as a solvent. An analysis by methods of the complete 2⁴ factorial design showed that an increase in the catalyst concentration gives a strong positive effect on the carvone conversion and selectivity. Hydrogen peroxide has a smaller positive effect on the conversion, but at high concentration, H₂O₂ leads to some decrease in the selectivity. An increase in the oxalic acid concentration has a beneficial effect on the conversion, but does not affect the selectivity.     

多金属氧酸盐催化苯甲醇的选择性氧化：一个绿色可循环的高效催化氧化体系

以Keggin结构的几类杂多酸和三乙胺（TEA）为原料,通过简单的酸碱反应合成了相应杂多酸的TEA盐。 并以它们作为催化剂,30％H2O2作氧化剂,在不使用长链相转移剂的条件下,研究了它们催化苯甲醇选择氧化制备苯甲醛的反应性能。 结果表明,该类催化剂在苯甲醇的选择氧化反应中具有比相应杂多酸更高的催化活性或选择性。 其中[TEAH]H2PW12O40为最佳催化剂,在适宜的反应条件下,该催化剂上苯甲醇转化率可达99.5％以上,苯甲醛选择性达~100％。 催化剂可以被分离和循环使用多次,活性、选择性基本不变。 用水作溶剂,避免了有机溶剂的使用,是一个高效、绿色的苯甲醛选择氧化体系。     

Organic solvent‐free catalytic hydrogenation of diene‐based polymer nanoparticles in latex form. Part II. Kinetic analysis and mechanistic study

The central challenge that has limited the development of catalytic hydrogenation of diene‐based polymer latex (i.e., latex hydrogenation) in large‐scale production pertains to how to accomplish the optimal interplay of accelerating the hydrogenation rate, decreasing the required quantity of catalyst, and eliminating the need for an organic solvent. Here, we attempt to overcome this dilemma through decreasing the dimensions of the polymer substrate (such as below 20 nm) used in the hydrogenation process. Very small diene‐based polymer nanoparticles were synthesized and then used as the substrates for the subsequent latex hydrogenation. The effects of particle size, temperature, and catalyst concentration on the hydrogenation rate were fully investigated. An apparent first‐order kinetic model was proposed to describe the rate of hydrogen uptake with respect to the concentration of the olefinic substrate (C?C). Mass transfer of both the hydrogen and catalyst involved in this solid (polymer)–liquid (water)–gas (hydrogen) three‐phase latex system is discussed. The competitive coordination of the catalyst between the C?C and acrylonitrile units within the copolymer was elucidated. It was found that (1) using very small diene‐based polymer nanoparticles as the substrate, the hydrogenation rate of polymer latex can be increased vastly to achieve a high conversion of 95% while a quite low level of catalyst loading is required; (2) this latex hydrogenation process was completely free of organic solvent and no cross‐linking was found; (3) the mass transfer of hydrogen is not a rate‐determining step in the present hydrogenation reactions; (4) the catalyst was dispersed homogeneously within the polymer nanoparticles; (5) for the reaction that has reached about 95 mol % conversion, the kinetic study shows that the reaction is chemically controlled with an apparent activation energy of 100–110 kJ/mol; (6) the strong coordination of C[tbond]N to the catalytically active species RhH₂Cl(PPh₃)₂ imposed a negative effect on the hydrogenation activity. The present research provides a comprehensive study to appreciate the underlying chemistry of latex hydrogenation of diene‐based polymer nanoparticles and more importantly shows great promise toward the commercialization of a “green” catalytic hydrogenation operation of a diene‐based polymer latex in industry. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Selective oxidation of alcohols to aldehydes by hydrogen peroxide using hexamolybdochromate(III) as catalyst

Anderson type hexamolybdochromate(III) was utilized as a catalyst for facile conversion of various aliphatic, benzylic and heterocyclic alcohols to corresponding aldehydes and ketones in good yields. The reaction was carried out in 50% aq. acetonitrile using hydrogen peroxide as the oxidant at 50 °C. The reaction was found to involve oxidation of the catalyst to its active Cr(V) intermediate by hydrogen peroxide.     

Epoxidation of propylene with hydrogen peroxide catalyzed by heteropolyphosphatotungstate

The epoxidation of propylene with hydrogen peroxide catalyzed by a reaction-controlled phase transfer catalyst (RCPT) composed of quaternary ammonium heteropolyoxotungstates in acetonitrile medium is studied. The influence of several factors on the reaction is studied, such as the reaction temperature, the effect of H₂O amount, the reaction time, the effect of the catalyst amount, solvent effect and the recycle of the catalyst. Under mild conditions, H₂O₂ conversion is 98.6%, and propylene oxide (PO) selectivity based on H₂O₂ is 97.2%. During the epoxidation, the catalyst is dissolved in the solution. However, after H₂O₂ is used up, the catalyst can be recovered as a precipitate and can be recycled. We find that the recycled catalyst has similar catalytic activity as the fresh one.     

Application of electrochemically generated molybdenum‐based catalyst system to the ring‐opening metathesis polymerization of norbornene and a comparison with the tungsten analogue

This study describes the application of the electrochemically generated molybdenum‐based catalyst system MoCl₅? e^?? Al? CH₂Cl₂ to ring‐opening metathesis polymerization of bicyclo[2.2.1]hept‐2‐ene (norbornene). The results are compared with those previously obtained by the WCl₆? e^?? Al? CH₂Cl₂ system. The polymer product has been characterized by ¹H and ¹³C NMR, IR and gel‐permeation chromatography techniques. This molybdenum‐based catalyst system has led to a mainly trans stereoconfiguration (ca 60%) of the double bonds, in contrast to the polymer obtained with the tungsten‐based analogue, where the cis content is 60%. Analysis of the poly(1,3‐cyclopentylenevinylene) microstructure by ¹³C NMR spectroscopy revealed that the polymer having σ_c = 0.41 (fraction of double bonds with cis configuration) contains a slightly blocky distribution (r_tr_c > 1) of the double‐bond dyads (r_tr_c = 1.44). In addition, the influence of reaction parameters, e.g. reaction time, electrolysis time and catalyst aging time, on conversion has been analysed in detail. Copyright © 2005 John Wiley & Sons, Ltd.     

Highly selective oxidation of glucose to formic acid over synthesized hydrotalcite-like catalysts under base free mild conditions

Sustainable and renewable production of platform chemicals and fuels has been gradually rising. Formic acid is one of the important chemicals for leather, cosmetic and pharmaceutical industries as well as hydrogen source. In this study, selective oxidation of biomass-derived glucose to formic acid was investigated under base free medium at 70 °C over synthesized hydrotalcite-like catalysts using hydrogen peroxide as oxidant. Effect of Mg/Al ratio (6/1, 3/1, 1/1, 1/3 and 1/6) and heat treatment (drying and calcination) on catalyst structure and product distributions; effect of calcination temperature (450, 650 and 900 °C), solvent composition (ethanol/water) and reaction temperature (30, 50 and 70 °C) on catalytic activity and product selectivity were investigated. Reducing the Mg/Al ratio enhanced the density of metal-OH bonds, surface area and uniformity of pores up to some extent. The highest glucose conversion and formic acid selectivity were achieved over Mg–Al (1:3) catalyst as 38.7 and 99.0%, respectively. The calcined catalysts (at 450 °C) exhibited 7 times higher selectivities and 4 times higher activities than the dried ones. However, higher calcination temperatures did not show remarkable increments in activities and yields. Easily prepared, cheap Mg–Al (1:3) catalyst provided promising results even at low temperature with hydrogen peroxide at atmospheric medium in a low boiling point solvent (ethanol).

Graphical abstract

     

Monomer/polymer Schiff base copper(II) complexes for catalytic oxidative polymerization of 2,2′‐dihydroxybiphenyl

Catalytic oxidative polymerization of 2,2′‐dihydroxybiphenyl (DHBP) was performed by using both the Schiff base monomer‐Cu(II) complex and Schiff base polymer‐Cu(II) complex compounds as catalysts and hydrogen peroxide as oxidant, respectively. The dependence of monomer conversion and molecular weight distribution on various reaction parameters, including time, temperature, solvent as well as the amount of catalyst and oxidant were investigated. The structure of the poly‐2,2′‐dihydroxybiphenyl (PDHBP) was confirmed by UV‐vis, IR, ¹H and ¹³C NMR spectroscopy techniques. The electrochemical and thermal properties of PDHBP were also studied. DSC data revealed that PDHBP was amorphous. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2977–2984, 2009     

Oxidation of 4-methoxy-1-naphthol on promoted platinum catalysts

Oxidative coupling of naphthols is a useful method for the formation of new carbon-carbon bonds in organic synthesis. In the presence of hydrogen peroxide, platinum supported on activated carbon catalyses this reaction. The outcome is influenced by the solvent, the reaction temperature and the physical structure of the catalyst. The catalyst structure is determined by the synthesis method and the modifier used (Bi or Sb). Within 40 min 4-methoxy-1-naphthol can be converted to 4,4'-dimethoxy-2,2'-binaphthalenyl-1,1'-diol with a yield of up to 94%, or to 4,4'-dimethoxy-2,2'-binaphthalenylidene-1,1'-dione with a yield of 92%. High amounts of quinoid byproducts (≤22%) are observed in nitromethane as the solvent.