Zinc-catalyzed aerobic oxidation of benzoins and its extension to enantioselective oxidation

Zn(II)-DABCO complex is used as an efficient catalyst for the aerobic oxidation of benzoins to benzils in the presence of molecular oxygen. Usage of chiral zinc complex as catalyst resulted in enantioselective oxidative kinetic resolution of racemic benzoin to yield enantiomerically enriched benzoins.     

Fe-Anderson型多金属氧酸盐和苯磺酸基低共熔溶剂仿生体系的构建及其柴油绿色氧化脱硫

在过去的几十年里,人们越来越关注环境污染问题.柴油中的硫化物燃烧后可转化为SOx,对环境造成严重污染.因此,为了满足严格的国家标准要求,生产硫化物含量极低的燃料油是一个巨大挑战.氧化脱硫(ODS)体系是用于深度脱硫的加氢脱硫(HDS)体系的替代或补充,包括硫化物的氧化和氧化产物的分离.它是处理芳香硫化合物及其衍生物最有效的方法之一,引起了人们的极大关注.在我们之前的工作中报道了Co聚阴离子催化剂和对甲苯磺酸基低共熔剂(DESs)通过仿生方法将柴油中的硫化物氧化为相应的硫化物.尽管已经取得了很大的进展, DESs仿生体系仍然有很大的发展空间.例如,多金属氧酸盐(POMs)在生物模拟体系中的作用没有得到明确阐述.更困难的是构建DES的物理化学性质与仿生体系氧化脱硫效率之间的关系.因此,解决上述问题是催化氧化脱硫(AODS)仿生过程中最关键的挑战之一,迫切需要进一步研究.本文采用仿生方法研究了一种新型高效的AODS体系,该体系能显著提高ODS的效率.采用重结晶法制备了安德森型催化剂Na3Fe(OH)6Mo6O18,并将其应用于柴油AODS体系.通过分析紫外-可见光谱(UV-Vis)、红外光谱(FT-IR)以及气质联用光谱(GC-MS),我们推测了通过多步电子转移AODS体系的仿生机理.首先, POM和氧气形成过氧聚阴离子,然后与苯磺酸形成苯基过氧磺酸.由于过氧磺酸盐对富电子的硫原子具有很高的选择性,所以它优先攻击硫原子.因此,二苯并噻吩被氧化成二苯并噻吩砜.还原后的苯磺酸和POM被氧气氧化,形成新的催化循环.这些结果表明,耦合氧化还原体系和ETMs通过低能量途径将电子从苯磺酸基DES转移到氧化剂,从而促进了反应过程.最终,二苯并噻吩易被氧化为二苯并噻吩砜.DES的物理性质表明,在60℃时, n(PEG2000)/n(BSA)=2.5体系中DES粘度最大,推测可能是氢键较强所致.此外,PEG2000/2.5BSA体系脱硫效果也是最好的.这一结果表明,脱硫体系的活性与氢键的强度有关.将该仿生策略应用于模型柴油的AODS中,在60 min内二苯并噻吩脱除率达到95%,表现出前所未有的性能,并且该仿生体系也可以成功应用于真实柴油的氧化脱硫.该催化剂可重复使用五次,且反应活性无明显降低,表明该催化体系具有商业应用潜力.     

Synthesis and characterization of some tetrazoles and their prospective for aerobic micro-fouling mitigation

Two series of tetrazole derivatives of the type N-(1H-tetrazol-5-yl)-1-(aryl)methanimine (101–106) and 1-(4-alkoxyphenyl)-N-(1H-tetrazol-5-yl)methanimine (107–111) were synthesized and characterized via conventional tools of analysis (elemental analysis, FT-IR and ¹H NMR spectroscopy). These two synthesized series were biologically evaluated for their potentials against some microbial biofilm causing strains (micro bio-foulants). Biological activities were evaluated by MIC values and cell viability percentages of them. In case of compounds (107–111), 107 was the most potent antimicrobial one, where its MIC values were 10.666667 µg/ml; 12.82222 µg/ml and 21.43666 µg/ml for Staphylococcus aureus, Escherichia coli and Candida albicans respectively, whereas compound 106, (of group 101–106), MIC values were 16 µg/ml for all the tested microorganisms. Viability assay showed that 107 activity percentages were 96.99456%, 92.32886% and 89.09558% against Gm +ve bacteria, Gm −ve bacteria and yeast respectively, whereas 106 activity percentages were 95.255569%, 90.204675% and 86.710956% against Gm +ve bacteria, Gm −ve bacteria and yeast respectively. Two antimicrobial mode of actions were proposed and discussed depending on the two evaluated tetrazole groups.     

Magnetic methylene-based mesoporous organosilica composite-supported IL/Pd: a powerful and highly recoverable catalyst for oxidative coupling of phenols and naphthols

A novel magnetic methylene-based mesoporous organosilica composite-supported IL/Pd complex (Fe₃O₄@MePMO-IL/Pd) was synthesized and characterized, and its catalytic performance was investigated. The preparation of the Fe₃O₄@MePMO composite was achieved through coating of Fe₃O₄ nanoparticles with a mixture of tetramethoxysilane, bis(triethoxysilyl)methane, and (3-chloropropyl)-trimethoxysilane in the presence of cetyltrimethylammonium bromide surfactant. The Fe₃O₄@MePMO was then modified with alkyl imidazolium ionic liquid and palladium species to deliver the Fe₃O₄@MePMO-IL/Pd nanocatalyst. This catalyst was characterized using Fourier transform infrared, thermal gravimetric, wide-angle powder X-ray diffraction, low-angle powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, vibrating sample magnetometer, energy-dispersive X-ray, and nitrogen adsorption–desorption analyses. The Fe₃O₄@MePMO-IL/Pd was effectively used as a highly recoverable and durable catalyst for the selective oxidative coupling of phenols and 2-naphthols under aerobic conditions.     

Aerobic oxidative esterification of benzyl alcohols with catalytic tetrabromomethane under visible light irradiation

We report a useful method for the facile synthesis of aromatic esters from benzyl alcohols with molecular oxygen and catalytic tetrabromomethane in alcohol under visible light irradiation with a fluorescent lamp. This is the first metal-free reaction using molecular oxygen as the terminal oxidant.     

Copper-catalyzed aerobic oxidative coupling of terminal alkynes with α-carbonyl aldehydes: An expedient approach toward ynediones

An efficient and mild one-pot approach for copper-catalyzed aerobic oxidative coupling of α-carbonyl aldehydes with terminal alkynes toward ynediones has been developed. Moreover, a variety of ynediones were constructed under the optimized reaction conditions, and a plausible mechanism was presented based on a series of control experiments.     

Efficient 2,2,6,6‐Tetramethylpiperidine‐1‐oxyl/iron Catalyzed Aerobic Dehydrogenation of Hexanitrobibenzyl to Hexanitrostilbene

Hexanitrostilbene (HNS) was efficiently produced through the dehydrogenation of hexanitrobibenzyl (HNBB) with oxygen catalyzed by 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO)/ferrous chloride (FeCl₂) in 80% yield, and up to a 308 turnover number was achieved. First, TEMPO is used in the dehydrogenation and the influence of reaction time, temperature, solvent and the catalyst were discussed. A possible mechanism of this catalytic process is proposed and it is obtained that Fe(II) can abstract hydrogen from HNBB and the function of the function of TEMPO is to oxidize Fe(II)OOH to Fe(III)OO.     

Nickel(0) catalyzed oxidation of organosilanes to disiloxanes by air as an oxidant

We report here an efficient non-aqueous route to symmetrical disiloxanes from their corresponding organosilanes using Ni(COD)₂ with 3,4,7,8-tetramethyl-1,10-phenanthroline in air. Our methodology is very simple and high yielding. The reaction mechanism is also proposed.     

Aerobic oxidation of secondary benzylic alcohols and direct oxidative amidation of aryl aldehydes promoted by sodium hydride

We reported herein new reactivities and possible mechanistic implications of a simplest oxidant (NaH/air) uncovered on a broad range of useful transformations, including aerobic alcohol oxidations, allylic alcohol isomerizations and oxidations, cyclopropyl alcohol fragmentations, and direct aryl aldehyde oxidative amidations. These readily implementable transition-metal-free processes feature exceptional material accessibility, operational simplicity, and environmental compatibility, and add new dimensions to its synthetic utilities that are fairly robust yet had not previously been fully realized and systematically explored.     

Cesium hydroxide-promoted aerobic oxidation of sec-aromatic alcohols

A CsOH-promoted aerobic oxidation of sec-aromatic alcohols has been developed, using air as a free and clean oxidant, and providing aryl ketones in good to excellent yields.