Electrocatalytic oxidation of benzyl alcohol in alkaline medium on RuO2-coated titanium electrode

The heterogeneous electrocatalytic redox behaviour of RuO₂ electrodes fabricated by thermal decomposition is investigated with and without benzyl alcohol using cyclic voltammetric and potentiodynamic techniques. The cyclic voltammetric results show that benzyl alcohol oxidation is mediated by perruthenate ion electrogenerated at the electrode surface. Evaluation of kinetic parameters in relation to Tafel lines allows the postulation of a plausible reaction scheme in which benzyl alcohol adsorbs on the RuO₂ electrode surface and the rate determining step is chemical reaction between perruthenate and adsorbed species. The reaction orders with respect to benzyl alcohol and OH^– concentrations are 0.85 and 1, respectively. The results in galvanostatic electrolysis show that the major product for benzyl alcohol oxidation in an aqueous solution is benzaldehyde, and the organic yield is affected by such electrolysis conditions as t-butanol concentration, electrolysis current density, KOH concentration and electrolysis temperature.     

Synthesis of Salicylic Acid-Polystyrene Type Chelate Resin with a New Route

A new route to synthesize salicylic acid-polystyrene type chelate resin is developed. In the presence of Lewis acid catalyst SnCl₄, the chloromethylation reaction of crosslinked polystyrene microspheres (CPS) was first performed using 1,4-bis(chloromethoxy)butane which is un-carcinogenic as a chloromethylation reagent, and the chloromethylated crosslinked polystyrene microspheres (CMCPS) were obtained. Subsequently, the nucleophilic substitution reaction between the benzyl chloride groups on CMCPS microspheres and 5-amino salicylic acid (ASA) was conducted, and chelate resin ASA-CPS was successfully obtained. The effects of main factors on the nucleophilic substitution reaction were examined. The chelating property of the prepared ASA-CPS resin for Fe³⁺ ion was tested preliminarily. The experimental results show that the reaction rate of the nucleophilic substitution reaction between the benzyl chloride groups on CMCPS microspheres and ASA is independent of the concentration of the nucleophilic reagent ASA. Therefore, the reaction is a typical unimolecular substitution reaction, namely, the substitution reaction has a mechanism of S_N1. The solvent with stronger polarity is advantageous to the fracture of C-Cl bond of the benzyl chloride groups, so the polarity of the solvent influences the substitution reaction rate greatly. To increase the reaction temperature also makes for the substitution reaction. The ASA-CPS resin possesses very strong chelating ability towards Fe³⁺ ions by right of the synergism of chelation and electrostatic interaction., and the adsorption capacity can get up to 21 g/100 g.     

Photoinduzierte H-Abstraktionen an Benzylarylethern durch Benzophenon

Photoinduced H-Abstraction on Benzyl Aryl Ethers by Benzophenone The triplet state of benzophenone abstracts in benzene of benzyl aryl ether 6 hydrogen atom from the CH₂-group. The formed α-ether radicals 1 and diphenylhydroxymethyl radicals 8 react to form the three possible reaction products in statistical distribution. Benzaldehydes 2 and phenols 11 are formed in a side reaction. From quantum yield measurements of the benzophenone reduction in dependence upon the concentration of benzyl phenyl ether 6a follows a rate constant of the H-abstraction of 9.5 ·10⁵ M⁻¹s⁻¹ which is in good agreement with measurements in presence of naphthalene as a quencher. The quenching constant for benzophenone triplet by naphthalene is 2 · 10⁹ M⁻¹s⁻¹. For benzyl phenyl ethers substituted in the benzyl ring the reaction constant for the H-abstraction reaction was determined, ϱ = −0,68,     

十二烷基苯磺酸催化合成乙酸苄酯的研究

以苄醇和冰醋酸为原料,十二烷基苯磺酸(DBSA)为催化剂,合成了乙酸苄酯。研究了物料比、酯化时间、酯化温度和催化剂用量对酯化率的影响,确定了最佳工艺条件:n(冰醋酸)∶n(苄醇)=1∶6,酯化时间4.5 h,酯化温度40℃,DBSA用量为冰醋酸物质的量的3%时酯化率最高可达78.39%。     

Anodic oxidation of benzyl alcohol to benzaldehyde in the presence of both redox mediator and polymer-supported phase-transfer catalyst

Using a polymer-supported phase-transfer catalyst (PTC) and a redox mediator, Cl^–/OCl^–, the anodic oxidation of benzyl alcohol was studied. The polymer support used in this study was synthesized by the method of suspension polymerization. The results revealed that on decreasing the crosslinking and increasing the content of chloromethylstyrene in the polymer support, the number of phase transfer active sites, tri-n-butylphosphine, in the polymer-supported PTC increased. The anodic oxidation of benzyl alcohol in the presence of the redox mediator, Cl^–/OCl^–, and polymer-supported PTC occurred in the reaction controlled region when the stirring rate exceeded 400 r.p.m. The results also revealed that the current efficiency for the anodic oxidation of benzyl alcohol was mainly affected by the characteristics and weight of the polymer-supported PTC, the pH, and the concentration of benzyl alcohol. However, the temperature affected the current efficiency only slightly.     

Kinetics of synthesizing 2,4,6-tribromophenyl benzyl ether in a triphase catalysis

The reaction of benzyl bromide with 2,4,6-tribromophenol in an organic solvent/aqueous alkaline solution of KOH to synthesize 2,4,6-tribromophenyl benzyl ether by triphase catalysis was investigated. The macroporous and microporous polymer pellets that served to support the catalyst were prepared by reacting styrene monomers, chloromethylstyrene monomers, and divinylbenzene in a suspension polymerization. Tributylamine was then immobilized on the surface of the polymer pellet to form the three-phase phase-transfer catalysts. The effects of the rate of agitation, degree of cross-linking of the polymer, solvents, inorganic salts, and temperature on the conversion of benzyl bromide and the reaction rate in the three-phase catalytic reaction were investigated in detail. We recommend that a macroporous polymer pellet with a small degree of cross-linking be used to react in a highly polar solvent to obtain high conversion of benzyl bromide and a rapid reaction. © 1994 John Wiley & Sons, Inc.     

Homogeneous redox catalysis of the electroreduction of benzyl chloride

The reactions between benzyl chloride and radical anions derived from anthracene and 9,10-diphenylanthracene were studied by cyclic voltammetry and controlled-potential electrolyses in N,N-dimethylformamide solutions, for several concentrations of the aromatic hydrocarbons. The controlled-potential electrolyses for direct and catalytic homogeneous reduction of benzyl chloride on mercury showed toluene as being the main product in both cases. These results were used in the formulation of the overall catalytic mechanisms. The application of a new theoretical treatment for the cyclic voltammetric results, developed recently by Savéant and coworkers, allowed the establishment of the rate determining step and the calculation of the rate constant for the homogeneous electron transfer reaction between the anthracene radical anion and benzyl chloride. This resulted in a value of 1.8 × 10⁴ M^?1 s^?1. For 9,10-diphenylanthracene it was established the existence of a mixed kinetic control under normal experimental conditions. Using very low initial concentrations of the depolarizer it was possible to obtain for the rate constant the value of 5.0 × 10³ M^?1 s^?1.     

BENZYL ACETATE FROM PHASE TRANSFER CATALYZED ACETATE DISPLACEMENT OF BENZYL CHLORIDE

The overall production rate equation of benzyl acetate by L-L phase transfer catalyzed acetate displacement of benzyl chloride were derived. The experimental results of the effects of stirring speed, structure and amount of catalyst, reaction temperature, amount of sodium acetate, and phase volume-ratio on the production rate of benzyl acetate are elucidated with the rate equation. Benzyltributylammonium chloride is the recommended catalyst. The apparent activation energy of the displacement of benzyl chloride with the ion pairs of benzyltributylammonium acetate is 8.13kcal/mol. Sodium sulfate is a suitable salt to improve the partition coefficient of the phase transfer catalyst. The cocatalyst, sodium iodide, can greatly improve the production rate of benzyl acetate when its amount do not exceed 3 mol% of the substrate, benzyl chloride. Under the conditions of 5mol% benzyltributylammonium chloride, phase volume-ratio 0.429, stirring speed 520 rpm, reaction temperature 70°C, and 50% aqueous sodium acetate, about 80% yield of benzyl acetate can be obtained within 2 hrs. of reaction time.     

Xylan derivatives: Benzyl ethers,synthesis, and characterization

The -2,3-bis(benzyl ether) of xylan, a natural polysaccharide, has been prepared by using a new benzylation method. This method was first tested on methyl-β-D -xylopyranoside, the monomer model of xylan. It implies the use of potassium hydroxyde, a crown ether as a catalyst, and benzyl bromide as a benzylating agent. Perbenzylated xylan is obtained with a good yield (80%) in a one-step reaction. It is soluble in most organic solvents. The ¹³C- and ¹H-NMR spectra of this polymer were assigned and are typical of a regular linear polymer. Differential thermal analysis and thermogravimetry indicate the temperature range at which this polymer can be processed at high temperature. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67: 455–460, 1998     

竹纤维苯甲基化的改性研究

以接枝率为考察目标用正交试验探索了反应温度、碱用量、反应时间、氯化苄及助剂季铵盐的用量5个因素对天然竹纤维苯甲基化改性的影响,确定了最佳反应条件。在NaOH溶液用量 16 mL,反应温度 120℃,季铵盐用量 0.4 g,反应时间 3 h,氯化苄用量 15 mL 的条件下,竹纤维的接枝率达 143.68%。并通过FT-IR、SEM等分析方法对接枝的竹纤维微观结构进行了研究和表征。     

Ring-opening copolymerization of ε-caprolactone with 2,2-dimethyltrimethylene carbonate using N-heterocyclic carbene organocatalysts

Random copolymer of ε-caprolactone with 2,2-dimethyltrimethylene carbonate has been synthesized by using N-heterocyclic carbene organocatalysts for the first time. A series of N-heterocyclic carbenes namely, imidazol-2-ylidenes substituted at 1,3 position by benzyl, isopropyl, ethyl and methyl were demonstrated to bring about the metal-free ring-opening copolymerization of ε-caprolactone and 2,2-dimethyltrimethylene initiated by benzyl alcohol in THF. The influences of reaction conditions, such as monomer, catalyst, and initiator concentration, as well as reaction temperature and time on the copolymerization have been examined in detail. The results show that 1-isopropyl-3-benzyl imidazol-2-ylidene carbene was potent organic catalyst for the ring-opening copolymerization of cyclic esters to generate well-defined linear polyesters of controlled molecular weight and narrow polydispersity. ¹H NMR spectral data of copolymer obtained showed that the polymerization mechanism is in agreement with the activated monomer mechanism.     

二氧化硅负载离子液体在合成苄基甲苯中的应用

二氧化硅负载氯铝酸离子液体,催化甲苯与氯化苄的烷基化反应,考察了反应温度、反应压力、原料配比和空速对氯化苄转化率和苄基甲苯选择性的影响,得出最佳反应条件:反应温度70 ℃,反应压力0.3 MPa,n(氯化苄)∶n(甲苯)=1∶4,空速3.0 h^-1,在此反应条件下,氯化苄转化率达86.97%,苄基甲苯选择性达72.35%。     

Electrochemical reduction of benzaldehyde using Pt-Pb/Nafion® as electrode

The electrochemical reduction of benzaldehyde using Pt-Pb/Nafion® as electrode without supporting electrolyte in the liquid organic phase was investigated. A novel Pt-Pb/Nafion® electrode was prepared for the electrolysis of the organic compound in this solid polymer electrolyte (SPEO) system. A reaction mechanism is proposed. No benzyl alcohol was produced using fresh Nafion® as electrode. The selectivity of benzyl alcohol using Pt-Pb/Nafion® as an electrode was almost 100% and only a trace of hydrobenzoin byproduct was found in the catholyte. The optimum faradic yield of benzyl alcohol was 18.70 g F^–1. The primary factors affecting the current efficiency or faradic yield of the cathodic reduction of benzaldehyde to benzyl alcohol were cell voltage, solvent and temperature. The use of a Pt-Pb/Nafion® electrode in a SPE® system for the electrochemical reduction of benzaldehyde was found to be a feasible technique.     

Continuous gas–liquid aerobic oxidation of toluene catalyzed by [T(p-Cl)PPFe]2O in a series of three stirred tank reactors

The liquid-phase catalytic aerobic oxidation of toluene by [T(p-Cl)PPFe]₂O was studied in a series of three stirred tank reactors. The effects of operation mode (including semi-batch and continuous operation), reaction temperature, catalyst concentration, average residence time, and air flow rate on the oxidation process were examined. The experimental results showed that continuous oxidation had no advantage over the total yield and selectivity of benzaldehyde and benzyl alcohol in comparison with semi-batch oxidation. And the reaction temperature was the most significant factor influencing on continuous oxidation of toluene. It is also found that adopting sequentially decreased temperature in the three series reactors could improve the yield and selectivity of benzaldehyde and benzyl alcohol in this process. Under which at the higher conversion of toluene, the total yield to benzaldehyde and benzyl alcohol increased 17.05% or 43.62% respectively in comparison with adopting sequentially increased or same temperature in the three series reactors.     

Simplistic transesterification approach for the synthesis of benzyl salicylate over honeycomb monoliths coated with modified forms of zirconia as catalysts: Kinetics

The catalysts such as Al₂O₃/ZrO₂ with 2–10?wt% of Al₂O₃ were coated on honeycomb monoliths by dip-and-dry technique. These catalysts were also prepared in their powder form. All the catalysts (honeycomb and powder form) were characterized for their surface acidity, crystallinity, functionality, elemental analysis, and morphology. The catalytic activity of all the catalysts was performed in the transesterification of methyl salicylate with benzyl alcohol to synthesize benzyl salicylate. Reaction conditions like reaction time, reaction temperature, and the molar ratio of the reactants were varied to obtain the highest yield of benzyl salicylate. The 6% Al₂O₃/ZrO₂ coated on honeycomb exhibited the highest conversion of methyl salicylate at 383?K in 60?min. Kinetic studies were conducted to determine the energy of activation and temperature coefficient. The rate constants in the case of 6AZ (HCM) was found to be 5.0?×?10^?3?min^?1 (373?K); 6.4?×?10^?3?min^?1 (383?K) and 2.2?×?10^?3?min^?1 (373?K); 3.2?×?10^?3?min^?1 (383?K) in the case of 6AZ (PF) catalyst, while the energy of activation (E_a) values were found to be 35.12 and 39.93 kJ mol^?1 for 6AZ (HCM) and 6AZ (PF), respectively. The reactant preadsorption study discloses that the transesterification follows the Eley–Rideal mechanism. Reactivation and recyclability of the catalysts were also examined and the results clearly indicate that Al₂O₃/ZrO₂ coated on the honeycomb is efficient and green catalytic system.     

硼杂碳包镍负载钯催化芳香醇需氧氧化

以硼杂碳包镍(Ni@BC)为载体,采用乙醇还原前驱体H_2PdCl_4法制备了一种新型磁可分离Pd/Ni@BC催化剂,并对其进行AAS、TEM、XRD和XPS表征,选取苯甲醇需氧氧化为探针反应,考察催化剂用量、反应温度和反应时间对催化性能的影响,研究催化剂对其他芳香醇的催化性能和循环使用性能。AAS结果表明,Pd负载质量分数为9.1%,与理论负载量一致。TEM结果显示,Pd纳米颗粒均匀分散在载体表面,平均粒径为4 nm。XRD和XPS结果均表明,催化剂的活性物种为Pd0。在反应温度80℃、O2_压力101.325 k Pa(流速20 m L·min~(-1))、CH_3CN为溶剂和K_2CO_3为碱性助剂条件下,Pd/Ni@BC对多种芳香醇的氧化反应表现出很高的催化活性和选择性,能将苯甲醇、对甲基苯甲醇、对乙基苯甲醇、对异丙基苯甲醇、肉桂醇、安息香、二苯甲醇以及邻甲基苯甲醇等定量转化为相应的醛或酮。催化剂重复使用5次,苯甲醇转化率由97.3%降至78.9%,Pd的少量脱落和部分氧化是催化剂活性降低的主要原因。     

Benzylation of benzene to diphenylmethane using zeolite catalysts

The catalytic liquid phase benzylation of benzene to diphenylmethane (DPM) with benzyl chloride (BC) is investigated over a number of zeolite catalysts at 358 K and under atmospheric pressure. Conventional homogeneous Lewis acid catalyst, AlCl₃, is also included for comparison. Zeolite H-β is found to be more selective but less active compared to HY and H-ZSM-5 zeolites in the benzylation of benzene. The conversion of BC, rate of BC conversion and selectivity to DPM over H-β after 6 h of reaction time are 33.3 wt%, 4.7 × 10⁻³ mmol g⁻¹ h⁻¹ and 89.1 wt%, respectively. For comparison, the conversion of BC, rate of BC conversion and selectivity to DPM over AlCl₃, under identical reaction condition, are found to be 100 wt%, 170 × 10⁻³ mmol g⁻¹ h⁻¹ and 58 wt%, respectively. Higher amounts of consecutive products are obtained over AlCl₃ due to its non shape selectivity. The acidity of the zeolite catalysts is measured by temperature programmed desorption method. The effect of the duration of the run, SiO₂/Al₂O₃ ratio of H-β, catalyst concentration, reaction temperature and benzene to BC molar ratio on the catalyst performance is also investigated in order to optimize the conversion of BC and selectivity for DPM. The conversion of BC using H-β is increased with the increase in the reaction time, catalyst concentration, reaction temperature and molar ratios whereas it decreases with the increase in SiO₂/Al₂O₃ molar ratio of H-β. H-β is recycled two times and a slight decrease in BC conversion is observed after each cycle, which is related to the minor dealumination of the zeolite catalyst by HCl, which is produced during the reaction as by product. The formation of DPM is explained by an electrophilic attack of the benzyl cation (C₆H₅CH₂⁺) on the benzene ring, which is produced by the polarization of BC over acidic sites of the zeolite catalysts.     

Anodic oxidation of benzyl alcohol to benzaldehyde in the presence of both redox mediator and phase transfer catalyst

The anodic oxidation of benzyl alcohol has been studied in the two-phase system containing both the redox mediator, ClO^-/Cl^-, and a phase transfer catalyst (PTC). The reaction mechanism and the factors which affect the current efficiency of benzaldehyde production were explored. The experimental results reveal that the rate determining step shifts from the shuttling rate of the redox ions to the anodic oxidation of Cl^- when the agitation rate changes from 400 to 500 rpm in the presence of 0.05m Bu₄NHSO₄. The results also show that benzyl alcohol is mainly oxidized in the organic phase by the shuttling of the ClO^-/Cl^- mediator. The current efficiency is mainly governed by the pH value and the nature of the organic solvent as well as the types and the concentration of PTC. The current efficiency is slightly affected by both the current density and temperature.     

有机锡催化合成乙酸苄酯新工艺研究

以新型不同类型的有机锡化合物为催化剂,对乙酸苄酯的酯化反应进行了研究,重点考察了不同类型的有机锡催化剂的催化效果、催化剂用量、反应温度、反应时间、酸醇摩尔比和带水剂等因素对乙酸苄酯产率的影响。实验结果表明,Ph3SnCl对合成乙酸苄酯有着良好的催化活性,当催化剂用量为苯甲醇和乙酸总质量1．5％,乙酸和苯甲醇的摩尔比为2．5：1,甲苯为10mU与苯甲醇的摩尔比为0．60）,温度110℃,反应150min后,乙酸苄酯产率可达98．4％．且催化剂重复使用5次仍保持较高活性。     

光稳定剂二苯甲酮合成新工艺研究

以苯甲酰氯、三氯化苄和苯为原料合成二苯甲酮,分别研究了反应温度、反应时间、原料配比、催化剂用量、溶剂的用量等条件对合成反应的影响,确定了最佳工艺条件。该方法合成二苯甲酮的最适宜的工艺条件是:反应温度120℃、反应时间12 h、n(苯甲酰氯)∶n(苯)=1∶1.7,n(苯甲酰氯)∶n(三氯化苄)=7.35∶1,催化剂用量为4.25 g(相对于0.588 mol苯甲酰氯),二苯甲酮的收率可达到94.54%以上,产品纯度二苯甲酮99.5%。