Preparation of 1-butyl-3-methylimidazolium dodecatungstophosphate and its catalytic performance for esterification of ethanol and acetic acid

1-Butyl-3-methylimidazolium dodecatungstophosphate catalyst ([bmim]₃PW₁₂O₄₀) with high water tolerance was prepared from 1-butyl-3-methylimidazolium bromide ([bmim]Br) and phosphotungstic acid (H₃PW₁₂O₄₀). The catalyst was characterized by means of Fourier transform infrared spectroscopy, thermogravimetry-differential scanning calorimetry, n-BuNH₂ potentiometric titration, elemental analysis and so on. Its catalytic activity for esterification of ethanol and acetic acid to ethyl acetate was measured. The results show that there were three crystal-water molecules in the [bmim]₃PW₁₂O₄₀ catalyst, and it preserved the primary Keggin structure and acid strength of H₃PW₁₂O₄₀. The acid amount of [bmim]₃PW₁₂O₄₀ catalyst was less than that of H₃PW₁₂O₄₀. The [bmim]₃PW₁₂O₄₀ catalyst exhibited higher catalytic activity and reusability in the esterification of ethanol and acetic acid to ethyl acetate. __________ Translated from Chinese Journal of Catalysis, 2008, 29(7) (in Chinese)     

Mesostructure organic‐inorganic hybrid ionic liquids based on heteropoly acids: Effect of linkage on the molecular structure and catalytic activity

The new inorganic–organic hybrids based on SO₃H‐functionalized ionic liquids (ILs) and Keggin‐type heteropoly acids (H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₄SiW₁₂O₄₀; HPAs) are prepared and characterized by FT‐IR, NMR, XRD, CV, SEM/EDX, ICP‐OES, BJH and UV. Different molecular structures according to the different inorganic part were also proved. Potentiometric titration showed a good relationship between catalytic activity and acidity of the catalysts. Electrochemical aspects showed electron transfer ability of the compounds. For understanding catalytic activities of the HPA‐IL hybrids in N‐formylation reaction, effect of catalyst composition, substrate, and reaction conditions were studied. The best SO₃H‐functionalized ionic liquid catalyst was readily recovered and reused for four runs. Easy preparation of the catalyst, simple and easy work‐up, mild reaction conditions, low cost, excellent yields and short reaction times are the key features of this work.     

Hydrolysis of cellulose by the heteropoly acid H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>

The potential of heteropoly acid H₃PW₁₂O₄₀ to catalyze the hydrolysis of cellulose to glucose under hydrothermal conditions was explored. This technology could contribute to sustainable societies in the future by using cellulose biomass. A study to optimize the reaction conditions, such as the amount of catalyst, reaction time, temperature, and the amount of cellulose used, was performed. A remarkably high yield of glucose (50.5%) and selectivity higher than 90% at 453 K for 2 h with a mass ratio of cellulose to H₃PW₁₂O₄₀ of 0.42 were achieved. This was attributed to the high hydrothermal stability and the excellent catalytic properties, such as the strong Brønsted acid sites. This homogeneous catalyst can be recycled for reuse by extraction with diethyl ether. The results illustrate that H₃PW₁₂O₄₀ is an environmentally benign acid catalyst for the hydrolysis of cellulose.     

Selective Conversion of Cellobiose and Cellulose into Gluconic Acid in Water in the Presence of Oxygen,Catalyzed by Polyoxometalate‐Supported Gold Nanoparticles

Gold nanoparticles loaded onto Keggin‐type insoluble polyoxometalates (Cs_xH_3?xPW₁₂O₄₀) showed superior catalytic performances for the direct conversion of cellobiose into gluconic acid in water in the presence of O₂. The selectivity of Au/Cs_xH_3?xPW₁₂O₄₀ for gluconic acid was significantly higher than those of Au catalysts loaded onto typical metal oxides (e.g., SiO₂, Al₂O₃, and TiO₂), carbon nanotubes, and zeolites (H‐ZSM‐5 and HY). The acidity of polyoxometalates and the mean‐size of the Au nanoparticles were the key factors in the catalytic conversion of cellobiose into gluconic acid. The stronger acidity of polyoxometalates not only favored the conversion of cellobiose but also resulted in higher selectivity of gluconic acid by facilitating desorption and inhibiting its further degradation. On the other hand, the smaller Au nanoparticles accelerated the oxidation of glucose (an intermediate) into gluconic acid, thereby leading to increases both in the conversion of cellobiose and in the selectivity of gluconic acid. The Au/Cs_xH_3?xPW₁₂O₄₀ system also catalyzed the conversion of cellulose into gluconic acid with good efficiency, but it could not be used repeatedly owing to the leaching of a H⁺‐rich hydrophilic moiety over long‐term hydrothermal reactions. We have demonstrated that the combination of H₃PW₁₂O₄₀ and Au/Cs_3.0PW₁₂O₄₀ afforded excellent yields of gluconic acid (about 85 %, 418 K, 11 h), and the deactivation of the recovered H₃PW₁₂O₄₀–Au/Cs_3.0PW₁₂O₄₀ catalyst was not serious during repeated use.     

Keggin Heteropolyacid Catalyzed Synthesis of Isoxazolo[5,4-d]pyrimidine-4,6(5H,7H)-diones at Room Temperature

Isoxazolo[5,4‐d]pyrimidine‐4,6(5H,7H)diones 2a – 2f have been synthesized from the reaction of ethyl 5‐amino‐3‐methyl‐4‐isoxazole carboxylate ( 1 ) with aryl isocyanates in the presence of Keggin heteropolyacid H₃[PW₁₂O₄₀] as a green solid acid catalyst at room temperature in a one‐pot process in good yields.     

Convenient regioselective reaction in presence of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>: synthesis and characterization of pyrazolo[3,4-<Emphasis Type="Italic">b</Emphasis>]quinoline-3,5-diones

We describe regioselective synthesis of pyrazolo[3,4-b]quinoline derivatives by multicomponent reaction of dimedone, 5-aminopyrazolone, and aromatic aldehydes in presence of H₃PW₁₂O₄₀ as catalyst. When this multicomponent reaction was investigated without catalyst under reflux conditions, a mixture of products was obtained, while the reaction successfully proceeded to formation of pyrazolo[3,4-b]quinoline in presence of H₃PW₁₂O₄₀. Good product yield, short experimental time, and low-cost catalyst provide convenient synthesis for formation of pyrazolo[3,4-b]quinoline pharmacological compounds.     

Efficient Method for the Synthesis of 1,5‐Benzodiazepine Derivatives Catalyzed by Monoammonium Salt of 12‐Tungstophosphoric Acid

Monoammonium salt of 12‐tungstophosphoric acid [(NH₄)H₂PW₁₂O₄₀] was found to be a practical, inexpensive, reusable, and efficient heterogeneous catalyst for the preparation of 1,5‐benzodiazepine derivatives of o‐phenylenediamine and ketones. The heteropolyacid‐based catalyst has the advantages of simple workup procedure, water insolubility with good activity, and high‐yielding reaction for the synthesis of 1,5‐benzodiazepine derivatives.     

Synthesis of Cs2.5H0.5PW12O40/TiO2 Nanocomposites with Dominant TiO2 {001} Facets and Related Photocatalytic Properties

TiO₂ nanosheets with dominant {001} facets, coupled with Cs_2.5H_0.5PW₁₂O₄₀, were successfully synthesized by a one‐step hydrothermal reaction. The photocatalytic activity of nanocatalysts was evaluated by the degradation of Rhodamine B under UV light irradiation. The results showed that both the addition of Cs_2.5H_0.5PW₁₂O₄₀ and the exposed {001} facets of TiO₂ have a positive effect on the photocatalytic activity. The improved photoactivity of nanocomposites in comparison with that of TiO₂ nanosheets could be attributed to the synergistic effect between Cs_2.5H_0.5PW₁₂O₄₀ and TiO₂ which facilitates the separation of photo‐induced hole‐electron pairs.     

三维有序大孔H3PW12O40-SiO2功能材料的制备、表征及催化性能研究

以杂多酸 H₃PW₁₂O₄₀ (PW₁₂)与正硅酸乙酯(TEOS)混合溶胶, 采用胶晶模板法结合煅烧去除模板工艺, 成功地制备了PW₁₂/SiO₂物质的量比在1/10～1/40之间的三维有序大孔(3DOM) PW₁₂-SiO₂催化剂. 经SEM, N₂吸附, XRD和FTIR等研究表明, PW₁₂含量较低的样品, 大孔结构三维规整性十分好. 在410 ℃氧化分解胶晶的条件下, PW₁₂基本保持一级Keggin结构. PW₁₂在样品中以分子簇或微晶存在, 其大小随含量增加而增大. PW₁₂高含量时, 其含氧键的FTIR振动与纯PW₁₂的基本一致, 但低含量时含氧键振动有一定偏移, 显示PW₁₂/SiO₂相互作用较显著. 样品酸性随杂多酸含量增加而增加, 但PW₁₂/SiO₂物质的量比超过1/30时酸性便减小, 呈火山型曲线变化规律. 对1-十二烯烷基化反应的催化活性随PW₁₂/SiO₂物质的量比的变化与酸性变化有相同的规律. 但所有样品的催化反应活性均远高于纯PW₁₂, 并且有良好的重复使用性能, 使用4次后仍保持新鲜催化剂活性的78%.     

（TEAH）nH3-nPW12O40催化苯甲醇选择氧化及其反应机理

以Keggin结构的磷钨酸和三乙胺（TEA）为原料,通过简单的酸碱反应合成了磷钨酸的TEA盐.并以它们为催化剂,考察了以H₂O₂为氧化剂、以水为溶剂的体系中苯甲醇选择氧化制备苯甲醛的反应性能.结果表明,（TEAH）_nH_3-nPW₁₂O₄₀（n=1,2,3）系列催化剂对苯甲醇的选择氧化反应有很高的活性和选择性,且可被分离和循环使用.在适宜的反应条件下,最佳催化剂（TEAH）H₂PW₁₂O₄₀上,苯甲醇的转化率可达99.6%,苯甲醛的选择性为100%.还采用IR,³¹PNMR谱和元素分析技术,对催化剂和反应过程中催化剂物种的转化和分布进行了考察,进而导出了反应机理.在这个水--油两相反应中,（PW₁₂O₄₀）^3-首先在H₂O₂的作用下,氧化降解为溶于水的小分子过氧物种（PO₄（WO（O₂）₂）₄）^3-和自由W物种.（PO₄（WO（O₂）₂）₄）^3-是真正的活性物种,可将部份溶于水层的苯甲醇氧化为苯甲醛,自身转变为失去活性氧的反应后物种（SAR）.而SAR又可与自由W物种一起聚合为前驱体状态的（PW₁₂O₄₀）^3-,完成催化循环.     

Acetylation of Alcohols Catalyzed by Dodeca-tungsto(molybdo)phosphoric acid

Summary. Acetylation of primary, secondary, and tertiary alcohols was carried out in some refluxing alkyl acetates and in two carboxylic acids with the participation of catalytic amounts of H₃PW₁₂O₄₀, H₃PMo₁₂O₄₀, and H₁₄P₅W₃₀O₁₁₀ with good yields and high stereo(regio)specificity under mild reaction condition. H₃PW₁₂O₄₀ and H₃PMo₁₂O₄₀ have also shown excellent reactivity in the formylation of 1-butanol with ethyl formate at room temperature and in short reaction times. Heteropolyacid catalysts could be separated after a simple work up and reused for several times.     

A Simple Polyoxometallate for Selective Oxidation of Benzyl Alcohol to Benzaldehyde with Hydrogen Peroxide

A series of Keggin‐type polyoxometallates, M₃(PW₁₂O₄₀)₂ [M=Ni, Zn, Co, Mn, Cu], FePW₁₂O₄₀, Ni₃(PMo₁₂O₄₀)₂ and Ni₂SiW₁₂O₄₀, were prepared and used as catalysts for selective oxidation of benzyl alcohol into benzaldehyde with H₂O₂ as an oxidant under solvent‐free condition. Ni₃(PW₁₂O₄₀)₂·26H₂O afforded high catalytic activity with TON of 550.6 mol/(mol cat.) and 87.3% selectivity. However, this catalyst can be easily recovered and reused.     

Impregnation of tungstophosphoric acid on poly(methacrylamide-co-methyl methacrylate) and its acid catalytic activity in TMB alkylation

A poly(methacrylamide-co-methylmethacrylate) (abbreviated PMAA-MMA) polymer support was studied for supporting a heteropolyacid (tungstophosphoric acid, H₃PW₁₂O₄₀) with its surface positively charged in the polymerization step. PMAA-MMA supports could be obtained in a porous form by eliminating template reagent molecules (benzylmalonic acid) combined with properly selected monomer (methacrylamide). The amount of amine groups in PMAA-MMA directly determined the amount of H₃PW₁₂O₄₀ impregnated, because the amine groups induced a positive charge on the PMAA-MMA surface. Finally, H₃PW₁₂O₄₀/PMAA-MMA showed better acid catalytic activities than unsupported H₃PW₁₂O₄₀ in alkylation of 1,3,5-trimethylbenzene with cyclohexene, which confirmed that PMAA-MMA supported H₃PW₁₂O₄₀ effectively.     

Preparation and Photocatalytic Activity of Mesoporous TiO2 Photocatalyst Co‐doped with Fe and H3PW12O40

The mesoporous titanium dioxide (MTiO₂) photocatalysts co‐doped with Fe and H₃PW₁₂O₄₀ were synthesized by template method using tetrabutyl titanate (Ti(OC₄H₉)₄), Fe(NO₃)k₃9H₂Oand H₃PW₁₂O₄₀ as precursors and Pluronic P123 as template. The as‐prepared photocatalyst was characterized by N₂ adsorption‐desorption measurements, X‐ray diffraction (XRD), scanning electron microscopy (SEM) and UV‐vis adsorption spectroscopy, and the photocatalytic activities of the prepared samples under UV and visible light were estimated by measuring the degradation rate of methyl blue (MB) (50 mg/L) in an aqueous solution. The characterizations indicated that the photocatalysts possessed a homogeneous pore diameter of ca. 10 nm with high surface area of ca. 150 m²/g. The results of MB photodecomposition showed that co‐doped mesoporous TiO₂ exhibited higher photocatalytic activities than un‐doped, single‐doped mesoporous TiO₂ under UV and visible light irradiation. It was shown that the co‐doped MTiO₂ could be activated by visible light and could thus be used as an effective catalyst in photo‐oxidation reactions. The synergistic effect of Fe and H₃PW₁₂O₄₀ co‐doping played an important role in improving the photocatalytic activity.     

Boehmite nano‐particles functionalized with silylpropylamine‐supported Keggin‐type heteropolyacids: Catalysts for epoxidation of alkenes

Boehmite nano‐particles with a high degree of surface hydroxyl groups were covalently functionalized by 3‐(trimethoxysilyl)‐propylamine to support H₃[PMo₁₂O₄₀], H₃[PW₁₂O₄₀], H₄[SiMo₁₂O₄₀] and H₄[SiW₁₂O₄₀] Keggin‐type heteropolyacids. After characterization of these catalysts by FT‐IR, powder X‐ray diffraction, TG/differential thermal analysis, CHN, inductively coupled plasma and transmission electron microscopy techniques, they were applied to the epoxidation of cis‐cycloocten. The progress of the reactions was investigated by gas–liquid chromatography, and the catalytic procedures were optimized for the parameters involved, such as the solvent and oxidant. The results showed that 25 mg of supported H₃[PMo₁₂O₄₀] catalyst in 1 ml C₂H₄Cl₂ with 0.5 mmol cyclooctene and 1 mmol tert‐butylhydroperoxide at reflux temperature gave 98% yield over 15 min. Recycling experiments revealed that these nanocatalysts could be repeatedly applied up to five times for a nearly complete epoxidation of cis‐cycloocten. The optimized experimental conditions were also used successfully for the epoxidation of some other alkenes, such as cyclohexene, styrene and α‐methyl styrene.     

Kinetics of the synthesis of propyl and butyl acrylates in the presence of some heteropolyacids as catalysts

Esterification reactions of acrylic acid with n‐propanol and n‐butanol were carried out in the liquid phase in the presence of H₃PW₁₂O₄₀ or H₃PMo₁₂O₄₀ as a catalyst, at various temperatures, molar ratios of the reactants, and concentrations of the catalyst. The kinetic equations had a nonelementary form. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 12–17, 2009     

Classical Keggin Intercalated into Layered Double Hydroxides: Facile Preparation and Catalytic Efficiency in Knoevenagel Condensation Reactions

The family of polyoxometalate (POM) intercalated layered double hydroxide (LDH) composite materials has shown great promise for the design of functional materials with numerous applications. It is known that intercalation of the classical Keggin polyoxometalate (POM) of [PW₁₂O₄₀]^3? (PW₁₂) into layered double hydroxides (LDHs) is very unlikely to take place by conventional ion exchange methods due to spatial and geometrical restrictions. In this paper, such an intercalated compound of Mg_0.73Al_0.22(OH)₂ [PW₁₂O₄₀]_0.04?0.98 H₂O (Mg₃Al‐PW₁₂) has been successfully obtained by applying a spontaneous flocculation method. The Mg₃Al‐PW₁₂ has been fully characterized by using a wide range of methods (XRD, SEM, TEM, XPS, EDX, XPS, FT‐IR, NMR, BET). XRD patterns of Mg₃Al‐PW₁₂ exhibit no impurity phase usually observed next to the (003) diffraction peak. Subsequent application of the Mg₃Al‐PW₁₂ as catalyst in Knoevenagel condensation reactions of various aldehydes and ketones with Z‐CH₂‐Z′ type substrates (ethyl cyanoacetate and malononitrile) at 60 °C in mixed solvents (V_2‐propanol:V_water=2:1) demonstrated highly efficient catalytic activity. The synergistic effect between the acidic and basic sites of the Mg₃Al‐PW₁₂ composite proved to be crucial for the efficiency of the condensation reactions. Additionally, the Mg₃Al‐PW₁₂‐catalyzed Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate demonstrated the highest turnover number (TON) of 47 980 reported so far for this reaction.     

Catalytic Decomposition of Lignin Model Compounds to Aromatics over Acidic Catalysts

Recent progress on the catalytic decomposition of lignin model compounds to aromatics was reported in this review. Cesium-exchanged heteropolyacid catalysts (Cs_xH_3.0?xPW₁₂O₄₀), palladium catalysts supported on cesium-exchanged heteropolyacid (Pd/Cs_xH_3.0?xPW₁₂O₄₀), and palladium catalysts supported on various activated carbon aerogels (ACAs) (Pd/ACA-SO₃H (X), Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA, Pd/Cs_xH_3.0?xPW₁₂O₄₀/ACA, and Pd/Cs_2.5H_0.5PW₁₂O₄₀/ACA-SO₃H) were prepared, and they were employed for the decomposition of C–O bond in lignin to aromatics. Phenethyl phenyl ether, benzyl phenyl ether, and 4-phenoxyphenol were used as dimeric lignin model compounds representing for β-O-4, α-O-4, and 4-O-5 bonds in lignin, respectively. It was observed that Cs_xH_3.0?xPW₁₂O₄₀ and Pd/Cs_xH_3.0?xPW₁₂O₄₀ were highly active for the decomposition of phenethyl phenyl ether and benzyl phenyl ether to aromatics. However, these catalysts showed very low catalytic performance in the decomposition of 4-phenoxyphenol. Palladium catalysts supported on various ACAs (Pd/ACA-SO₃H (X), Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA, Pd/Cs_xH_3.0?xPW₁₂O₄₀/ACA, and Pd/XCs_2.5H_0.5PW₁₂O₄₀/ACA-SO₃H) were efficient for the decomposition of 4-phenoxyphenol to aromatics. Acidity of the catalysts played a key role in determining the catalytic performance in the decomposition of 4-phenoxyphenol to aromatics.     

One‐Pot Synthesis of 5,7,8,9,9a,10‐Hexahydro‐8‐thioxotetrahydropyrido[2,3‐d : 6,5‐d′]dipyrimidine‐2,4,6(1H,3H,5aH)‐triones via a Four‐Component Coupling Reaction of Aldehydes,Amines, Barbituric Acids,and Thiouracil

An efficient one‐pot approach to the synthesis of 5,7,8,9,9a,10‐hexahydro‐8‐thioxopyrido[2,3‐d : 6,5‐d′]dipyrimidine‐2,4,6(1H,3H,5aH)‐triones 5 via a four‐component reaction of an aldehyde 1 , an amine 2 , a barbituric acid 3 , and thiouracil ( 4 ) is reported for the first time. This new multicomponent reaction is accomplished in refluxing EtOH in the presence of tungstophosphoric acid (H₃PW₁₂O₄₀) as a catalyst. A variety of hexahydropyrido[2,3‐d : 6,5‐d′]dipyrimidinetrione derivatives were successfully synthesized in excellent yields with this protocol (Table 2).     

Efficient synthesis of xanthenedione derivatives using cesium salt of phosphotungstic acid as a heterogeneous and reusable catalyst in water

Cs_2.5H_0.5PW₁₂O₄₀ has been reported to be an efficient catalyst for the synthesis of 1,8-dioxo-octahydroxanthene from aldehydes and 1,3-cyclohexanedione/dimedone in water. This approach is environmentally benign with clean synthetic procedure, short reaction time, easy workup procedure, excellent yield, and regeneration of catalyst, which made this protocol efficient and safe.