Oxone/CaCl_2/TEMPO体系在温和条件下对醇的氧化反应

Oxone/TEMPO/CaCl_2(TEMPO=2,2,6,6-Tetramethyl-1-piperidinyloxy)是一种稳定安全和易得的氧化催化体系,在室温条件下,可以氧化苄基或烷基醇生成醛或酮.苄基伯醇很容易被氧化成相应的醛,有较高的反应收率(90%～96%),仲醇氧化成相应的酮,收率在81%～85%之间,1,4-丁二醇环氧化生成γ-丁内酯得到了94%的收率.     

将醇控制氧化成醛或酮的催化体系

介绍一种有效催化醇氧化成醛或酮反应的新型催化剂(TEMPO/CuCl),涉及醇的氧化、配位、电负性等高中化学知识,供一线教师用于新课标高中“有机化学基础”模块课程教学。     

Oxone/CaCl2/TEMPO体系在温和条件下对醇的氧化反应

Oxone/TEMPO/CaCl₂ (TEMPO＝2,2,6,6-Tetramethyl-1-piperidinyloxy)是一种稳定安全和易得的氧化催化体系, 在室温条件下, 可以氧化苄基或烷基醇生成醛或酮. 苄基伯醇很容易被氧化成相应的醛, 有较高的反应收率(90%～96%), 仲醇氧化成相应的酮, 收率在81%～85%之间, 1,4-丁二醇环氧化生成γ-丁内酯得到了94%的收率.     

离子液体-水介质中离子液体负载TEMPO催化选择氧化合成脂肪醇羟基芳香醛和酮

由于脂肪醇羟基和苄醇羟基具有相同的氧化反应活性,所以当分子内同时含有脂肪醇羟基和苄醇羟基时,很难选择氧化苄醇羟基合成含脂肪醇羟基的芳香醛或酮。本文报道了在离子液体-水介质中,NCS/NaBr/IL-TEMPO（离子液体负载TEMPO）催化氧化合成含有脂肪醇羟基的芳香醛、酮的方法,反应条件温和,选择性好,收率高,且离子液体和催化剂可以循环使用。     

以Saccharin/TEMPO高效催化氧化醇制备醛酮的研究

采用Saccharin/TEMPO共催化剂并在次氯酸钠NaClO作用下高效地催化氧化醇合成了醛或酮。筛选了溶剂及SAC/TEMPO用量等条件获得了最优工艺。以一系列的醇作为底物进行了研究,结果表明,高效地实现了对醇的氧化转化,产率可达95%,并且有良好的选择性。应用此共催化体系对醛或酮的制备具有广泛的适用性,是一种较好的方法。     

CuBr/1,8-二氮杂双环[5.4.0]十一碳-7-烯催化苄醇的选择性空气氧化反应（英文）

发展了一种新型、实用性的以溴化亚铜为催化剂,以1,8-二氮杂双环[5.4.0]十一碳-7-烯(DBU)为添加剂,在空气条件下进行氧气氧化苄醇的催化体系.各种一级或二级苄醇及烯丙醇可以以高的产率及选择性转换为相应的醛和酮.该过程为无溶剂反应,同时不需要使用四甲基哌啶氧化物(TEMPO)类助氧化剂.     

有机碲氧化物催化合成α,β-不饱和酮和2,4-二烯酮

α,β-不饱和酮是重要的有机合成中间体,常用醇钠或氢氧化钠作催化剂由醛酮缩合合成,这时常由于强碱而发生副反应。Cava曾报道双对-甲氧苯基氧化碲(BMPTO)对醇醛缩合有一定催化作用。本文以BMPTO为催化剂,通过Claisen-Schmidt反应合成了一系列α,β-不饱和酮和2,4-二烯酮。所得产物及其结构表征结果列于表1。     

聚合物微球固载的催化剂TEMPO在分子氧氧化环己醇过程中的催化特性

醇氧化为羰基化合物是有机合成工业中最重要的化学转变之一,在实验室研究和精细化工生产中都占有非常重要的地位.使用传统的化学计量强氧化剂(如CrO3, KMnO4, MnO2等),不但成本高及反应条件苛刻,还会产生大量污染环境的废弃物.因此,需要大力发展高效、绿色化的醇转变为羰基化合物的氧化途径.以2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)为催化剂,分子氧为氧化剂,可在温和条件下绿色化地实现醇的氧化转变.该催化氧化作用的实质是TEMPO经过单电子氧化过程转化为相应的氮羰基阳离子,该阳离子是一个具有强氧化性的氧化剂,可将伯醇和仲醇分别快速地、高转化率、高选择性地氧化为对应的醛或酮.然而,目前使用的TEMPO大多为均相催化剂,虽然表现出良好的催化活性和选择性,但反应后难以分离回收,不能再循环使用,严重制约着这一催化体系的发展.本文将TEMPO化学键合在聚合物载体上,在非均相催化剂的作用下,以期实现环已醇的分子氧氧化,将其转变为环已酮.首先采用悬浮聚合法,制备了交联聚甲基丙烯酸缩水甘油酯(CPGMA)微球,该聚合物微球表面含有大量环氧基团,为实现TEMPO的固载化提供了条件.以4-羟基-2,2,6,6-四甲基哌啶氮氧自由基(4-OH-TEMPO)为试剂,使CPGMA微球表面的环氧基团发生开环反应,从而将TEMPO键合于微球表面,制得了固载有TEMPO的聚合物微球TEMPO/CPGMA.将此非均相催化剂与Fe(NO3)3组成共催化体系,应用于分子氧氧化环己醇的催化氧化过程,深入考察了该共催化体系的催化性能,并探索研究了催化氧化机理,考察了主要条件对催化氧化反应的影响.结果表明,共催化体系TEMPO/CPGMA+Fe(NO3)3可以有效地催化分子氧氧化环己醇的氧化过程,将环己醇转化为唯一的产物环己酮,显示出良好的催化选择性.助催化剂Fe(NO3)3化学结构中的Fe3+离子和NO3–离子两种物种均参与催化过程,共同发挥助催化剂的作用,伴随着两种价态铁物种Fe(Ⅱ)与Fe(Ⅲ)的转变以及NO3–与NO2–之间的转变,固载化的氮氧自由基TEMPO不断地转变为氮羰基阳离子,该氧化剂物种使环己醇的氧化反应不断地循环进行.对于共催化体系TEMPO/CPGMA+Fe(NO3)3的使用,适宜的反应条件为TEMPO与Fe(NO3)3的摩尔比为1：1,55°C,通入常压O2.反应35 h,环己酮的转化率可达到44.1%.因此,在温和条件下,使用固载化的TEMPO,有效地实现了环己醇向环己酮的转化.此外,固载化催化剂TEMPO/CPGMA在循环使用过程中表现出良好的重复使用性能.     

聚合物微球固载的催化剂TEMPO在分子氧氧化环己醇过程中的催化特性（英文）

醇氧化为羰基化合物是有机合成工业中最重要的化学转变之一,在实验室研究和精细化工生产中都占有非常重要的地位.使用传统的化学计量强氧化剂(如Cr O3,KMnO4,MnO2等),不但成本高及反应条件苛刻,还会产生大量污染环境的废弃物.因此,需要大力发展高效、绿色化的醇转变为羰基化合物的氧化途径.以2,2,6,6-四甲基哌啶氮氧自由基(TEMPO)为催化剂,分子氧为氧化剂,可在温和条件下绿色化地实现醇的氧化转变.该催化氧化作用的实质是TEMPO经过单电子氧化过程转化为相应的氮羰基阳离子,该阳离子是一个具有强氧化性的氧化剂,可将伯醇和仲醇分别快速地、高转化率、高选择性地氧化为对应的醛或酮.然而,目前使用的TEMPO大多为均相催化剂,虽然表现出良好的催化活性和选择性,但反应后难以分离回收,不能再循环使用,严重制约着这一催化体系的发展.本文将TEMPO化学键合在聚合物载体上,在非均相催化剂的作用下,以期实现环已醇的分子氧氧化,将其转变为环已酮.首先采用悬浮聚合法,制备了交联聚甲基丙烯酸缩水甘油酯(CPGMA)微球,该聚合物微球表面含有大量环氧基团,为实现TEMPO的固载化提供了条件.以4-羟基-2,2,6,6-四甲基哌啶氮氧自由基(4-OH-TEMPO)为试剂,使CPGMA微球表面的环氧基团发生开环反应,从而将TEMPO键合于微球表面,制得了固载有TEMPO的聚合物微球TEMPO/CPGMA.将此非均相催化剂与Fe(NO3)3组成共催化体系,应用于分子氧氧化环己醇的催化氧化过程,深入考察了该共催化体系的催化性能,并探索研究了催化氧化机理,考察了主要条件对催化氧化反应的影响.结果表明,共催化体系TEMPO/CPGMA+Fe(NO3)3可以有效地催化分子氧氧化环己醇的氧化过程,将环己醇转化为唯一的产物环己酮,显示出良好的催化选择性.助催化剂Fe(NO3)3化学结构中的Fe3+离子和NO3–离子两种物种均参与催化过程,共同发挥助催化剂的作用,伴随着两种价态铁物种Fe(Ⅱ)与Fe(Ⅲ)的转变以及NO3–与NO2–之间的转变,固载化的氮氧自由基TEMPO不断地转变为氮羰基阳离子,该氧化剂物种使环己醇的氧化反应不断地循环进行.对于共催化体系TEMPO/CPGMA+Fe(NO3)3的使用,适宜的反应条件为TEMPO与Fe(NO3)3的摩尔比为1:1,55°C,通入常压O2.反应35 h,环己酮的转化率可达到44.1%.因此,在温和条件下,使用固载化的TEMPO,有效地实现了环己醇向环己酮的转化.此外,固载化催化剂TEMPO/CPGMA在循环使用过程中表现出良好的重复使用性能.     

纳米尺度氧化石墨烯层作为高效碳催化剂用于苄醇与芳香醛的绿色氧化

合成了纳米尺度氧化石墨烯(NGO)层,用作碳催化剂高效催化苄醇与芳香醛的氧化反应.对于醇氧化反应,当80℃时H2O2存在下,NGOs(20 wt％)可高效催化醇选择性生成醛,其反应速率和产率取决于醇上取代基的性质.对于4-硝基苄醇,反应24 h后,只有10％可转换为相应羧酸.相反,4-甲氧基苄醇和二苯基甲醇分别反应仅9和3h则可完全转化为对应的羧酸和酮.NGO碳催化剂上芳香醛氧化速率高于醇氧化速率.对于所有的醛,采用7 wt％ NGO作催化剂,在70℃反应2-3 h后,就可完全转化为相应羧酸.我们讨论了NGO催化剂结构对苄醇和芳香醛氧化反应影响的可能机理.     

Mild and selective oxidation of alcohols to aldehydes and ketones using NaIO4/TEMPO/NaBr system under acidic conditions

A TEMPO-catalyzed selective oxidation of alcohols to the corresponding aldehydes and ketones using NaIO₄ as the terminal oxidant is reported. The NaIO₄/TEMPO/NaBr system provides a mild and efficient method for the oxidation of alcohols that are sensitive to basic conditions. Furthermore, the recoverable ionic liquid immobilized TEMPO-catalyzed oxidation of benzyl alcohol in ionic liquid-H₂O medium is also developed.     

Efficient NO equivalent for activation of molecular oxygen and its applications in transition-metal-free catalytic aerobic alcohol oxidation

tert-Butyl nitrite (TBN) was identified as an efficient NO equivalent for the activation of molecular oxygen. The unique property of TBN enabled TEMPO-catalyzed aerobic alcohol oxidation to be performed in high-volume efficiency. Up to a 16,000 turnover number was achieved in this transition-metal-free aerobic catalytic system. Under the optimal reaction conditions, various alcohols were converted into their corresponding carbonyl compounds with TEMPO/HBr/TBN as catalyst. The newly developed method was suitable for the oxidation of solid substrate alcohols with high melting point and/or low solubility under the help of minimum solvent to form a slurry.     

Cu(bipy)2+/TEMPO-catalyzed oxidation of alcohols: radical or nonradical mechanism?

In the oxidation of alcohols with TEMPO as catalyst, the substrate has alternatively been postulated to be oxidized but uncoordinated TEMPO(+) (Semmelhack) or Cu-coordinated TEMPO(?) radical (Sheldon). The reaction with the Cu(bipy)(2+)/TEMPO cocatalyst system has recently been claimed, on the basis of DFT calculations, to not be a radical reaction but to be best viewed as electrophilic attack on the alcohol C-H(α) bond by coordinated TEMPO(+). This mechanism combines elements of the Semmelhack mechanism (oxidation of TEMPO to TEMPO(+)) and the Sheldon proposal ("in the coordination sphere of Cu"). The recent proposal has been challenged on the basis of DFT calculations with a different functional, which were reported to lead to a radical mechanism. We carefully examine the results for the two functionals and conclude from both the calculated energetics and from an electronic structure analysis that the results of the two DFT functionals are consistent and that both lead to the proposed mechanism with TEMPO not acting as radical but as (coordinated) positive ion.     

含环氧基团的聚合物微球固载2,2,6,6-四甲基哌啶氮氧自由基催化剂的制备及其催化分子氧氧化苯甲醇

以甲基丙烯酸缩水甘油酯(GMA)为单体, 以乙二醇二甲基丙烯酸酯(EGDMA)为交联剂, 采用悬浮聚合法制得交联聚甲基丙烯酸缩水甘油酯(CPGMA)微球, 然后以4-羟基-2,2,6,6-四甲基哌啶氮氧自由基(4-OH-TEMPO)为试剂, 使CPGMA微球表面的环氧基团发生开环反应, 从而制得了TEMPO固载化微球TEMPO/CPGMA, 考察了制备条件对固载化反应的影响, 并采用多种方法对微球TEMPO/CPGMA进行了表征. 将微球TEMPO/CPGMA与CuCl组成共催化体系, 用于分子氧氧化苯甲醇, 考察了反应条件对催化体系性能的影响. 结果表明, 以含环氧基团的聚合物微球CPGMA为载体, 通过开环反应, 可成功地实现TEMPO的固载化, 开环反应属S_N2亲核取代反应, 适宜采用溶剂N,N''-二甲基甲酰胺和反应温度85℃. 非均相催化剂TEMPO/CPGMA与助催化剂CuCl构成共催化体系, 在室温、常压O₂条件下可高效地将苯甲醇氧化为苯甲醛, 产物选择性和产率分别为100%和90%. 主催化剂TEMPO与助催化剂CuCl适宜的摩尔比为1:1.2; 主催化剂适宜用量为0.90 g. 此外, TEMPO/CPGMA固体催化剂具有良好的循环使用性能.     

Aerobic Oxidation of Benzyl Alcohol Catalyzed by Cu-Mn Mixed Oxides and 2,2,6,6-Tetramethyl-piperidyl- 1-oxy1

Heterogeneous Cu-Mn mixed oxides can mediate TEMPO-catalyzed selective oxidation of benzyl alcohol by molecular oxygen under neutral condition, and is recyclable. In the case of the molar ratio of Cu and Mn over 1, the highly-dispersed CuO inside the Cu-Mn mixed oxides is responsible for the good performances in catalytic oxidation.     

Laccase-catalyzed mediated oxidation of benzyl alcohol: the role of TEMPO and formation of products including benzonitrile studied by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry

Substituted benzyl alcohol was oxidized enzymatically with a laccase-mediator system and the products were investigated as a function of time by nanoelectrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (nanoESI-FTICRMS). With Trametes versicolor laccase (TVL), the mediator, 2,2',6,6'-tetramethylpiperidine-N-oxyl radical (TEMPO), undergoes oxidation and forms oxoammonium ion. Oxidized TEMPO oxidizes the alcohol and is simultaneously reduced to the N-OH form. The laccase then restores TEMPO back to the normal radical form and the oxidation cycle starts again. The role of TEMPO and the structures of its oxidized and reduced forms in the enzymatic oxidation process were clarified in collision-induced dissociation experiments and gas-phase hydrogen/deuterium (H/D) exchange reactions. The amounts of enzyme and mediator were significant for product formation: with greater amounts overoxidation products, the corresponding benzoic acid and benzonitrile were formed. Smaller amounts of laccase and mediator generated benzaldehyde in high yield. The reaction pathway for benzonitrile formation is discussed and it is suggested to start from benzaldehyde and the ammonia in the ammonium acetate buffer.     

2,2,6,6-四甲基哌啶氧自由基氧化糖类物质伯羟基研究进展

2,2,6,6-四甲基哌啶氧自由基(TEMPO)属于亚硝酰自由基类,能选择性氧化糖类物质的伯羟基,氧化产物的应用非常广泛。本文对TEMPO氧化糖类物质伯羟基的研究进展作一综述。     

Aerobic Oxidation of Benzyl Alcohol Catalyzed by Cu-Mn Mixed Oxides and 2,2,6,6-Tetramethyl-piperidyl-1-oxyl

Heterogeneous Cu-Mn mixed oxides can mediate TEMPO-catalyzed selective oxidation of benzyl alcohol by molecular oxygen under neutral condition, and is recyclable. In the case of the molar ratio of Cu and Mn over 1, the highly-dispersed CuO inside the Cu-Mn mixed oxides is responsible for the good performances in catalytic oxidation.     

TEMPO/HCl/NaNO2 catalyst: a transition-metal-free approach to efficient aerobic oxidation of alcohols to aldehydes and ketones under mild conditions

Hydrochloric acid, a very inexpensive and readily available inorganic acid, has been found to cooperate exquisitely with NaNO(2)/TEMPO in catalyzing the molecular-oxygen-driven oxidation of a broad range of alcohol substrates to the corresponding aldehydes and ketones. This transition-metal-free catalytic oxidative conversion is novel and represents an interesting alternative route to the corresponding carbonyl compounds to the metal-catalyzed aerobic oxidation of alcohols. The reaction is highly selective with respect to the desired product when carried out at room temperature in air at atmospheric pressure. Notably, the use of very inexpensive NaNO(2) and HCl in combination with TEMPO for this highly selective aerobic oxidation of alcohols in air at ambient temperature makes the reaction operationally and economically very attractive. The results of mechanistic studies, performed with the aid of electrospray ionization mass spectrometry (ESI-MS), are presented and discussed. TEMPO, TEMPOH, and TEMPO(+) were observed in the redox cycle by means of ESI-MS. On the basis of these observations, a mechanism is proposed that may provide an insight into the newly developed aerobic alcohol oxidation.     

A TEMPO‐Free Copper‐Catalyzed Aerobic Oxidation of Alcohols

The copper‐catalyzed aerobic oxidation of primary and secondary alcohols without an external N‐oxide co‐oxidant is described. The catalyst system is composed of a Cu/diamine complex inspired by the enzyme tyrosinase, along with dimethylaminopyridine (DMAP) or N‐methylimidazole (NMI). The Cu catalyst system works without 2,2,6,6‐tetramethyl‐l‐piperidinoxyl (TEMPO) at ambient pressure and temperature, and displays activity for un‐activated secondary alcohols, which remain a challenging substrate for catalytic aerobic systems. Our work underscores the importance of finding alternative mechanistic pathways for alcohol oxidation, which complement Cu/TEMPO systems, and demonstrate, in this case, a preference for the oxidation of activated secondary over primary alcohols.