Cu催化羟基自由基氧化断裂纤维二糖分子糖苷键反应及其在纤维素低温解聚中的应用（英文）

纤维素是葡萄糖通过β-1,4-糖苷键链接而成的高聚物,在木质纤维素中含量最高,结构稳定,较难水解.糖苷键的解聚主要有三种方式:酶水解、酸水解以及碱降解.酶解的优点是反应条件温和、副产物少,但存在成本高、活性低等缺点,限制了其大规模的工业化生产.碱水解纤维素的同时伴随着葡萄糖的peeling-off反应得到异变糖酸,需要消耗大量的碱,并且强碱也存在腐蚀性强和回收难等问题.酸水解是目前工业上常用的纤维素水解方法,在保持较高葡萄糖选择性的同时,通过对反应条件的控制(提高反应温度和酸浓度)来提高纤维素的水解效率,但是硫酸对设备的腐蚀性强,也难以回收,不符合绿色化学的发展要求.固体酸是近年来研究较多的纤维素水解催化剂.固体酸虽然腐蚀性弱、易回收,但是其活性低,水热稳定性较差,目前还不具备大规模生产的条件.本文发展了一种羟基自由基活化断裂糖苷键的方法,利用羟基自由基的高活性在低温下实现糖苷键的选择性断裂,同时羟基自由基与糖苷键作用后转化为无毒无害的水和氧气,将不会对环境造成污染.我们首先以纤维二糖作为纤维素的模型分子,通过羟基自由基能够优先与糖苷键反应得到葡萄糖和葡萄糖酸的实验证实所提出的方法的可...     

N-羟基邻苯二甲酰亚胺及其类似物催化下的分子氧氧化反应

本文综述了近年来N-羟基邻苯二甲酰亚胺（NHPI）及其类似物催化下分子氧氧化的各种反应,并对它们的催化机理作了简要介绍。NHPI与过渡金属离子组成的催化体系能高效的催化乙烷氧化为乙酸、环烷烃氧化为二元羧酸、甲苯氧化为苯甲酸、烯烃氧化为环氧化物、炔烃氧化为炔酮、酰胺氧化为酰亚胺;NHPI单独使用能催化金刚烷发生氧化羰基化反应、催化氧化醇制取过氧化氢;NHPI与有机助催化剂如：偶氮二异丁腈、溴化季铵盐、蒽醌、醇等也能催化分子氧氧化反应。     

二氟甲基自由基反应及其在18F标记中的应用

随着正电子发射断层扫描(PET)技术的进步, 高效¹⁸F标记反应显现出重大的研究价值. 同时, 在有机氟化学的快速发展下, 研究人员已开发出一系列产生二氟甲基自由基(·CHF₂)的一碳合成子, 得以被引入到¹⁸F标记反应中. 本文从化学原理出发, 总结了近年来·CHF₂合成子、 碳氢键活化反应及¹⁸F标记的研究, 并展望了未来的研究趋势.     

Cr-HMS合成、表征及其在催化氧化反应中的应用

合成了一系列不同Cr含量的CrHMS介孔分子筛,并对其物化性质进行了表征.结果表明,Cr的引入降低了介孔分子筛骨架结构的规整度和孔径的均一程度.CrHMS对苯羟基化和环己烷氧化反应均表现出良好的催化活性,并且随Cr含量的增加,催化活性呈火山型分布.对于较易进行的环己烷氧化反应,将CrHMS在H₂气氛中预先还原处理,可使催化剂既能保持较高的催化氧化活性,又能获得较好的稳定性.     

固载化N-羟基邻苯二甲酰亚胺在分子氧氧化二苯甲醇为二苯甲酮反应过程中的催化特性

采用简捷高效的方法在交联聚苯乙烯(CPS)微球表面同步合成与固载了N-羟基邻苯二甲酰亚胺(NHPI),制备了非均相催化剂CPS-NHPI微球,我们将其用于分子氧对二苯甲醇的氧化过程,探索研究了其催化性能与催化氧化机理,并考察了主要因素对其催化性能的影响.研究结果表明,将固体催化剂微球CPS-NHPI与过渡金属盐组合形成复合催化剂,可有效地催化分子氧对二苯甲醇的氧化过程.在几种过渡金属盐中,助催化效果的顺序是VO(acac)2Co(OAc)2Co Cl2Mn(OAc)2.显然,乙酰丙酮氧钒盐的助催化效果最好.共催化体系CPS-NHPI+VO(acac)2可在温和条件(75℃、常压的氧气)下高效地将二苯甲醇催化氧化转变为二苯甲酮(二苯甲醇转化率为35.8%,且二苯甲酮是唯一产物),显示出良好的催化活性与优良的催化选择性,催化氧化反应遵循自由基链式反应的机理.体积比为7∶3的乙腈与乙酸乙酯的混合液为适宜的反应溶剂;VO(acac)2与固载NHPI的摩尔比为1∶15时,助催化剂的投加量较为适宜.固体催化剂CPS-NHPI还具有良好的再循环使用性能.     

N-羟基邻苯二甲酰亚胺(NHPI)用于有机氧化反应的研究进展

综述了N-羟基邻苯二甲酰亚胺(NHPI)及其类似物作为电化学氧化基质和催化剂用在有机氧化反应中的研究进展。对它们的合成,在催化体系中的作用和催化氧化反应机理作了重点评述。     

自然氧化偶联及其在碳氢功能化反应中的应用

氧化偶联作为一种经济、高效的化学键构建模式,在有机合成化学中得到了广泛的应用.近年来, Klussmann、焦宁和霍聪德等课题组通过发展简单、直接的自然氧化偶联反应,成功实现了一些Csp³-H和Csp²-H功能化反应,在该领域中取得了重要进展.我们就他们近年来在该领域的研究进展作一亮点评述.     

聚合物微球固载的N-羟基邻苯二甲酰亚胺在分子氧氧化甲苯过程中的催化性能

以交联聚苯乙烯(CPS)微球为基质,经过几步大分子反应在微球表面合成与固载了N-羟基邻苯二甲酰亚胺(NHPI),形成固载有NHPI的聚合物微球CPS-NHPI。本文主要将CPS-NHPI与过渡金属盐组成共催化体系,用于分子氧氧化甲苯的反应,考察了该非均相催化剂的催化特性与催化氧化机理。结果表明,几种过渡金属盐中,Co(OAc)2的助催化效果最好;微球CPS-NHPI与Co(OAc)2所构成的共催化体系,在温和条件(80℃和常压氧气)下可有效地将甲苯深度氧化为苯甲酸,显现出高的催化活性(甲苯转化率达到57%)与优良的选择性(苯甲酸的选择性达到84%)。催化氧化反应遵循自由基链式反应机理。主催化剂CPS-NHPI固载的NHPI与助催化剂Co(OAc)2适宜的摩尔比为14∶1,主催化剂所含NHPI为底物的12(mol)%时,催化剂用量较为合适。固体催化剂CPS-NHPI具有良好的再循环使用性能。     

N-羟基邻苯二甲酰亚胺与8-羟基喹啉氧钒(Ⅳ)配合物协同催化分子氧氧化乙苯

研究了钒化合物对N-羟基邻苯二甲酰亚胺(NHPI)催化分子氧氧化乙苯反应中的调变效应.结果表明,由8-羟基喹啉及其衍生物与乙酰丙酮氧钒(Ⅳ)配位制得的8-羟基喹啉氧钒(Ⅳ)配合物的催化活性比乙酰丙酮氧钒(Ⅳ),NH4VO3和V2O5的高.在优化的反应条件下,乙苯转化率和苯乙酮选择性可分别达60％～69％和97％.基于液...     

Study of depolymerization of cotton cellulose by Pb/PbO2 anode electrochemical catalysis in sulfuric acid solution

A novel method of cotton cellulose depolymerization is investigated in this paper. In this work, a three-electrode system, which contains a Pb/PbO₂ anode, two copper cathodes and a reference saturated calomel electrode (SCE), is applied to electrocatalytic depolymerization of cotton cellulose. After electrocatalytic depolymerization of cotton cellulose in 0.5M sulfuric acid solution using Pb/PbO₂ anode at room temperature (25 °C), the average degree of polymerization (DP) can be reduced to the minimum 367 from 1100. The effects of operating parameters, such as supporting electrolyte, current density and reaction time are investigated as well. The composition of the products in filtrate is characterized by phenol-sulfuric acid method, extraction, NMR, GC-MS and High Performance Liquid Chromatography (HPLC). In addition, the solid sample is analyzed via SEM images, XRD diffractogram, Ubbelohde capillary viscometer and FT-IR spectra. The results suggest that it is effective to convert cotton cellulose to soluble sugar, 5-hydroxymethylfurfural (5-HMF) and other products by electrocatalytic methods. However, the yield of products is low and needs further study. A novel method to significantly convert cotton cellulose to biofuels and biomaterials can be hopefully developed if the selectivity of cotton cellulose electrocatalytic depolymerization is improved in the future.     

Alkyne and ketone induced novel cleavage of a CC bond and a CSi bond in zirconacyclobutene-silacyclobutene fused ring compounds

Novel cleavage patterns of CC bonds and CSi bonds were achieved via alkyne- or ketone-induced reactions of zirconacyclobutene-silacyclobutene fused ring compounds; thermodynamically favored six-membered zirconacyclohexadiene derivatives were formed in excellent yields from the four-membered zirconacyclobutenes via this unprecedented alkyne-induced CC bond and CSi bond cleavage process.     

Photoreaction of anthracenyl phosphine oxides: Usual reversible photo- and heat-induced emission switching,and unusual oxidative PC bond cleavage

Anthracenyl(diphenyl)phosphine oxide and dianthracenylphenylphosphine oxide as photoactive compounds have been synthesized. Anthracenyl group of these compounds indicate the multi-functional roles such as an emission component, a photodimerization component, and a leaving group. When the light irradiation was performed under an oxygen atmosphere, photo-oxidative PC bond cleavage to leave the antharacenyl group was observed. Moreover, phosphonyl radical was produced and then PP bond formation to form diphosphane was observed.     

Cationic iridium-BINAP complex-catalyzed addition of aryl ketones to alkynes and alkenes via directed C-H bond cleavage

Cationic Ir complex ([Ir(cod)₂]BF₄ + BINAP) catalyzed the addition of ortho-C-H bonds in aryl ketones to alkynes, which gave alkenylated products in good to high yield. Styrene derivatives were good substrates, and the enantioselective addition to norbornene was also described.     

Chlorodimethylaluminum-promoted nucleophilic addition of lithium pentamethylcyclopentadienide to aliphatic aldehydes and DDQ-mediated carbon-carbon bond cleavage of the adducts providing the parent aldehydes

Treatment of aliphatic aldehyde with lithium pentamethylcyclopentadienide in the presence of chlorodimethylaluminum provided the corresponding carbinol in excellent yield. The carbinol returns to the parent aldehyde and pentamethylcyclopentadiene by the action of a catalytic amount of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ).     

Selective cleavage of the linear ether bond in benzyl glycidyl ether and triphenylmethyl glycidyl ether by potassium alkalide as two-electron-transfer reagent

The linear ether bond was exclusively cleaved in benzyl glycidyl ether and triphenylmethyl glycidyl ether under the influence of K⁻, K⁺(15-crown-5)₂ (1), whereas the strongly strained three-membered oxacyclic ring remained undisturbed. Potassium glycidoxide and benzylpotassium were found as the primary reaction products of benzyl glycidyl ether with 1. Subsequently, benzylpotassium reacted with benzyl glycidyl ether giving the next potassium glycidoxide molecule and bibenzyl. Benzyl phenyl ether was used as a model compound to explain the mechanism of bibenzyl formation. The reaction of triphenylmethyl glycidyl ether with 1 resulted in potassium glycidoxide and stable triphenylmethylpotassium. After treating with a quenching agent a new glycidyl ether or glycidyl ester was obtained from potassium glycidoxide. These results were found when the reaction occurred at the excess of glycidyl ether. In another case, i.e. at the excess of 1 further reactions took place with the participation of potassium anions and various new compounds were observed in the reaction mixture after benzylation or methylation. Thus, the method of substrates delivery influences the course of studied processes in a decisive way.     

Oxidative DNA cleavage by copper ternary complexes of 1,10-phenanthroline and ethylenediamine-sulfonamide derivatives

Ternary copper(II) complexes (1–3) of 1,10-phenanthroline and ethylenediamine-R-sulfonamide derivatives (R = benzene, toluene and naphthalene rings) have been synthesized and characterized with the aid of X-ray diffraction and spectroscopic and electrochemical techniques. The crystal structures of the complexes show that the coordination polyhedron around copper(II) is distorted square planar. Both 1,10-phenanthroline and ethylenediamine-R-sulfonamide act as bidentate ligands. The three structures are stabilized by π–π stacking interactions. The interaction of the complexes with calf thymus DNA has been investigated by thermal denaturation studies which indicated that DNA was stabilized in the presence of the compounds. The increase in DNA stability induced by the complexes follows the order: 3 > 2 > 1. All three complexes were found to be very efficient agents of plasmid DNA cleavage in the presence of ascorbate as reducing agent. Mechanistic studies of the DNA cleavage process performed with radical scavengers show that the reactive oxygen species involved in the DNA damage are the hydroxyl radical, singlet oxygen-like species, the superoxide* and hydrogen peroxide.     

Pentamethylcyclopentadienide in organic synthesis: nucleophilic addition of lithium pentamethylcyclopentadienide to aromatic aldehydes and carbon-carbon bond cleavage of the adducts affording the parent aldehydes

Treatment of aromatic aldehyde with lithium pentamethylcyclopentadienide provided the corresponding carbinol in excellent yield. The carbinol returns to the parent aldehyde and pentamethylcyclopentadiene upon exposure to an acid or due to heating. The combination of the two reactions can represent a protection of aromatic aldehyde.     

Pentamethylcyclopentadienide in organic synthesis: nucleophilic addition of lithium pentamethylcyclopentadienide to carbonyl compounds and carbon-carbon bond cleavage of the adducts yielding the parent carbonyl compounds

Lithium pentamethylcyclopentadienide (C₅Me₅Li, Cp*Li) reacted with aromatic aldehyde to provide the corresponding carbinol in excellent yield. The carbinol returns to the parent aldehyde and pentamethylcyclopentadiene upon exposure to acid or due to heating. Chlorodimethylaluminum is essential as an additive to attain the nucleophilic addition of Cp*Li to aliphatic aldehyde. The carbinol derived from aliphatic aldehyde returns to the parent aldehyde and pentamethylcyclopentadiene by the action of a catalytic amount of 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ). The reversible addition/elimination of the Cp* group can represent a protection of aldehyde. Mechanistic details of the carbon-carbon bond cleavage are also disclosed.