Development of a General and Efficient Iron‐Catalyzed Epoxidation with Hydrogen Peroxide as Oxidant

The development of inexpensive and practical iron catalysts for the environmentally benign epoxidation of olefins with hydrogen peroxide as terminal oxidant is described. By systematic variation of ligands, metal sources, and reaction conditions, it was discovered that FeCl₃?6H₂O in combination with pyridine‐2,6‐dicarboxylic acid and different amines shows high reactivity and excellent selectivity towards the epoxidation of aromatic olefins and moderate reactivity towards that of aliphatic olefins.     

金属卟啉催化的过氧化氢选择氧化烃类反应机理研究

本文综合介绍了近年来采用过氧化氢为氧化剂,金属铁卟啉和锰卟啉模拟酶体系催化烯烃环氧化和烷烃氧化的反应机理。总结了采用不同手段促进过氧化氢的异裂,以有效形成金属卟啉活性中间体的反应过程。     

Selective Oxidation of Toluene with Hydrogen Peroxide Catalyzed by V-Mo-based Catalyst

The selective catalytic oxidation of toluene with hydrogen peroxide over V-Mo-based catalysts under mild conditions was studied.The promotion effect of Mo on the catalysts was studied with V/Al2O3 and Mo/Al2O3 as reference samples.The catalysts were characterized by XRD,TPR,and XPS techniques.The results show that the addition of Mo to V/Al2O3 may change the distribution of V species on Al2O3 surface.Over V-Mo/Al2O3 catalyst,highly dispersed amorphous V species facilitates benzaldehyde formation,and crystalline V2O5 species increases the conversion of toluene but decreases the selectivity to benzaldehyde,while AlVMoO7 species favors both the conversion of toluene and the formation of cresols.The yield of benzaldehyde depends remarkably on the surface O/Al and Mo/V atomic ratios,and gets to a maximum value of 13.2% with a selectivity of 79.5% at an O/Al atomic ratio of 3.0 and Mo/V atomic ratio of 0.7.     

钼、钨过氧配合物催化过氧化氢氧化烯烃和醇类反应的研究进展

综述了在钼、钨过氧配合物催化下，用清洁氧化剂对过氧化氢氧化醇类和烯烃 的最新研究进展。     

Quinone‐Catalyzed Selective Oxidation of Organic Molecules

Quinones are common stoichiometric reagents in organic chemistry. Para‐quinones with high reduction potentials, such as DDQ and chloranil, are widely used and typically promote hydride abstraction. In recent years, many catalytic applications of these methods have been achieved by using transition metals, electrochemistry, or O₂ to regenerate the oxidized quinone in situ. Complementary studies have led to the development of a different class of quinones that resemble the ortho‐quinone cofactors in copper amine oxidases and mediate the efficient and selective aerobic and/or electrochemical dehydrogenation of amines. The latter reactions typically proceed by electrophilic transamination and/or addition‐elimination reaction mechanisms, rather than hydride abstraction pathways. The collective observations show that the quinone structure has a significant influence on the reaction mechanism and has important implications for the development of new quinone reagents and quinone‐catalyzed transformations.     

水溶性金属卟啉催化过氧化氢氧化对苯二酚的动力学研究

我们利用紫外-可见分光光度法研究了25℃时金属卟啉Fe（TPPS）Cl和Co（TPPS）催化过氧化氢氧化对苯二酚（HQ）的动力学（其中,TPPS为四（p-磺酸钠苯基）卟啉）,探讨了体系酸度、过氧化氢／催化剂摩尔比、中心金属离子对催化反应的影响,提出了金属卟啉催化氧化对苯二酚的反应历程,建立了反应的动力学模型．研究结果表...     

Environmentally Benign Oxidation of Some Organic Sulfides with 34% Hydrogen Peroxide Catalyzed by Simple Heteropolyoxometalates

An environmentally benign oxygenation protocol was developed for selective oxidation of some types of aromatic and aliphatic sulfides in good to excellent yields utilizing 34% hydrogen peroxide catalyzed by simple heteropolyoxometalates in normal drinking water at room temperature. The catalysts could be recovered and reused for at least seven reaction cycles under the described reaction conditions without considerable loss of reactivity. This procedure introduced a new insight into the use of simple heteropolyanions as recoverable catalysts for the oxidation of organic sulfides by an environmentally acceptable protocol. Keywords     

固载离子液体刷/过氧磷钨酸盐催化剂催化H2O2选择性氧化硫醚

以二氧化硅为载体,合成了一种新型的双层离子液体刷固载过氧磷钨酸盐催化剂.采用元素分析、IR和SEM-EDAX等手段对催化剂进行了表征.室温下,考察了该催化剂催化30％(质量分数)H2O2溶液选择性氧化硫醚为亚砜或砜的催化性能.结果表明,该催化剂具有很高的催化活性和选择性.采用1.1倍H2O2时,反应选择性地生成亚砜,仅...     

Fe‐Catalyzed One‐Pot Oxidative Cleavage of Unsaturated Fatty Acids into Aldehydes with Hydrogen Peroxide and Sodium Periodate

A one‐pot method has been developed for the oxidative cleavage of internal alkenes into aldehydes by using 0.5 mol % of the nonheme iron complex [Fe(OTf)₂(mix‐bpbp)] (bpbp=N,N′‐bis(2‐picolyl)‐2,2′‐bipyrrolidine) as catalyst and 1.5 equivalents of hydrogen peroxide and 1 equivalent of sodium periodate as oxidants. A mixture of diastereomers of the chiral bpbp ligand can be used, thereby omitting the need for resolution of its optically active components. The cleavage reaction can be performed in one pot within 20 h and under ambient conditions. Addition of water after the epoxidation, acidification and subsequent pH neutralization are crucial to perform the epoxidation, hydrolysis, and subsequent diol cleavage in one pot. High aldehyde yields can be obtained for the cleavage of internal aliphatic double bonds with cis and trans configuration (86–98 %) and unsaturated fatty acids and esters (69–96 %). Good aldehyde yields are obtained in reactions of trisubstituted and terminal alkenes (62–63 %). The products can be easily isolated by a simple extraction step with an organic solvent. The presented protocol involves a lower catalyst loading than conventional methods based on Ru or Os. Also, hydrogen peroxide can be used as the oxidant in this case, which is often disproportionated by second‐ and third‐row metals. By using only mild oxidants, overoxidation of the aldehyde to the carboxylic acid is prevented.     

双氧水氧化苯乙烯制苯甲酸的机理研究

在苯乙烯100 mmol,n(钨酸钠)∶n(草酸)∶n(苯乙烯)∶n(30%H2O2)=2.0∶3.2∶100.0∶440.0,92℃的反应条件下,用GC-MS和GC-IR跟踪分析了反应物和反应产物。根据其含量随反应时间的变化关系,提出了苯乙烯氧化为苯甲酸可能经过两条途径的反应机理。     

Reactivity and Operational Stability of N‐Tailed TAMLs through Kinetic Studies of the Catalyzed Oxidation of Orange II by H2O2: Synthesis and X‐ray Structure of an N‐Phenyl TAML

The catalytic activity of the N‐tailed (“biuret”) TAML (tetraamido macrocyclic ligand) activators [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂NR}Cl]^2? ( 3 ; N atoms in boldface are coordinated to the central iron atom; the same nomenclature is used in for compounds 1 and 2 below), [X, R=H, Me ( a ); NO₂, Me ( b ); H, Ph ( c )] in the oxidative bleaching of Orange II dye by H₂O₂ in aqueous solution is mechanistically compared with the previously investigated activator [Fe{4‐XC₆H₃‐1,2‐( N COCMe₂ N CO)₂CMe₂}OH₂]^? ( 1 ) and the more aggressive analogue [Fe(Me₂C{CON(1,2‐C₆H₃‐4‐X) N CO}₂)OH₂]^? ( 2 ). Catalysis by 3 of the reaction between H₂O₂ and Orange II (S) occurs according to the rate law found generally for TAML activators (v=k_Ik_II[Fe^III][S][H₂O₂]/(k_I[H₂O₂]+k_II[S]) and the rate constants k_I and k_II at pH 7 both decrease within the series 3 b > 3 a > 3 c . The pH dependency of k_I and k_II was investigated for 3 a . As with all TAML activators studied to‐date, bell‐shaped profiles were found for both rate constants. For k_I, the maximal activity was found at pH 10.7 marking it as having similar reactivity to 1 a . For k_II, the broad bell pH profile exhibits a maximum at pH about 10.5. The condition k_I?k_II holds across the entire pH range studied. Activator 3 b exhibits pronounced activity in neutral to slightly basic aqueous solutions making it worthy of consideration on a technical performance basis for water treatment. The rate constants k_i for suicidal inactivation of the active forms of complexes 3 a – c were calculated using the general formula ln([S₀]/[S_∞])=(k_II/k_i)[Fe^III]; here [Fe^III], [S₀], and [S_∞] are the total catalyst concentration and substrate concentration at time zero and infinity, respectively. The synthesis and X‐ray characterization of 3 c are also described.     

Iron‐Promoted ortho‐ and/or ipso‐Hydroxylation of Benzoic Acids with H2O2

Regioselective hydroxylation of aromatic acids with hydrogen peroxide proceeds readily in the presence of iron(II) complexes with tetradentate aminopyridine ligands [Fe^II(BPMEN)(CH₃CN)₂](ClO₄)₂ ( 1 ) and [Fe^II(TPA)(CH₃CN)₂](OTf)₂ ( 2 ), where BPMEN=N,N′‐dimethyl‐N,N′‐bis(2‐pyridylmethyl)‐1,2‐ethylenediamine, TPA=tris‐(2‐pyridylmethyl)amine. Two cis‐sites, which are occupied by labile acetonitrile molecules in 1 and 2 , are available for coordination of H₂O₂ and substituted benzoic acids. The hydroxylation of the aromatic ring occurs exclusively in the vicinity of the anchoring carboxylate functional group: ortho‐hydroxylation affords salicylates, whereas ipso‐hydroxylation with concomitant decarboxylation yields phenolates. The outcome of the substituent‐directed hydroxylation depends on the electronic properties and the position of substituents in the molecules of substrates: 3‐substituted benzoic acids are preferentially ortho‐hydroxylated, whereas 2‐ and, to a lesser extent, 4‐substituted substrates tend to undergo ipso‐hydroxylation/decarboxylation. These two pathways are not mutually exclusive and likely proceed via a common intermediate. Electron‐withdrawing substituents on the aromatic ring of the carboxylic acids disfavor hydroxylation, indicating an electrophilic nature for the active oxidant. Complexes 1 and 2 exhibit similar reactivity patterns, but 1 generates a more powerful oxidant than 2 . Spectroscopic and labeling studies exclude acylperoxoiron(III) and Fe^IV?O species as potential reaction intermediates, but strongly indicate the involvement of an Fe^III? OOH intermediate that undergoes intramolecular acid‐promoted heterolytic O? O bond cleavage, producing a transient iron(V) oxidant.     

二氧化硅包覆的杂多酸在双氧水存在条件下催化氧化甘油

催化剂的酸性和氧化还原性在催化生物质平台分子转化过程中起着非常重要的作用,杂多酸具有较强的酸性以及优良的氧化还原性,因而杂多酸在生物质催化转化领域备受关注。本文利用溶胶-凝胶法和硅烷化方法将杂多酸催化剂封装在二氧化硅载体内部,随后以傅立叶红外光谱、X-射线衍射仪、热重分析仪、透射电子显微镜、扫描电镜等手段对合成的材料进行了表征。红外光谱表明杂多酸在催化剂中保持了其完整结构,X-射线衍射表明杂多酸高度分散在二氧化硅载体上,电镜表征显示催化剂呈球形纳米颗粒形貌。基于以上表征结果,我们将包覆的杂多酸催化剂应用于甘油氧化,在以过氧化氢为氧化剂,温和反应条件下,合成的材料对甘油氧化具有良好的催化活性,其中对甲酸的选择性大约为70%,对乙醇酸的选择性大约为27%。硅烷化过程对于催化剂循环起着重要的作用,单纯二氧化硅的比表面积为287 m²·g^-1,二氧化硅包覆杂多酸经过硅烷化后,其比表面积降为245 m²·g^-1,而且孔径也有所降低。单纯二氧化硅与水的接触角为0°,而二氧化硅包覆的杂多酸在硅烷化之后的催化剂具有很强的疏水性,与水的接触角为137°。根据这些催化剂表征数据说明硅烷化过程不仅可以显著提高催化剂的疏水性,而且同时限制了载体孔径,阻止杂多酸流失到反应体系中,与传统的浸渍法将杂多酸负载在二氧化硅载体上得到的催化剂相比,催化剂的循环利用性显著提高。反应后的催化剂结构与新鲜催化剂相比,并没有发生明显变化。催化剂经过一次循环后,表面暴露了更多的活性中心,活性稍有提高。催化剂在反应体系中加入强质子酸可以显著提高反应的催化性能,揭示了Bronsted酸在甘油氧化过程中对甘油分子的活化起着重要的作用。     

Photothermal Oxidation of Cinnamyl Alcohol with Hydrogen Peroxide Catalyzed by Gold Nanoparticle/Antimony-Doped Tin Oxide Nanocrystals

Gold nanoparticles with different mean sizes were formed on antimony-doped tin oxide nanocrystals by the temperature-varied deposition-precipitation method (Au/ATO NCs). Au/ATO NCs possess strong absorption in the near-infrared region due to Drude excitation in addition to the localized surface plasmon resonance (LSPR) of AuNPs around 530 nm. Au/ATO NCs show thermally activated catalytic activity for the oxidation of cinnamyl alcohol to cinnamaldehyde by hydrogen peroxide. The catalytic activity increases with a decrease in the mean Au particle size (d_Au) at 5.3 nm≤d_Au≤8.2 nm. Light irradiation (λ_ex >660 nm, ∼0.5 sun) of Au/ATO NCs increases the rate of reaction by more than twice with ∼95 % selectivity. Kinetic analyses indicated that the striking enhancement of the reaction stems from the rise in the temperature near the catalyst surface of ∼30 K due to the photothermal effect of the ATO NCs.