二氧化硅负载磷钼钒酸铯选择性催化硝化苯酚为邻硝基苯酚

采用溶胶-凝胶法制备了二氧化硅负载磷钼钒酸铯催化剂,利用XRD、红外、SEM以及物理吸附等技术手段对催化剂进行了表征分析,并以稀硝酸（30%）为硝化剂,考察了该催化剂对苯酚硝化反应的催化性能,系统研究了反应时间、催化剂用量、硝酸与苯酚用量以及催化剂重复利用等对催化反应的影响。 结果表明,制备的负载磷钼钒酸铯催化剂具有典型的Keggin结构,在温和的苯酚硝化反应条件下,表现出优良的催化活性和高的邻硝基苯酚选择性,在实验优化条件下,邻硝基苯酚收率达到88%,催化剂回收方便可多次重复使用。 负载磷钼钒酸铯催化苯酚硝化反应结合水蒸汽蒸馏提供了一种简单可行的制备邻硝基苯酚的方法。     

Cu-Mn spinel oxide catalyzed regioselective halogenation of phenols and N-heteroarenes

A novel simple, mild chemo- and regioselective method has been developed for the halogenation of phenols using Cu-Mn spinel oxide as a catalyst and N-halosuccinimide as halogenating agent. In the presence of Cu-Mn spinel oxide B, both electron-withdrawing and electron-donating groups bearing phenols gave monohalogenated products in good to excellent yields with highest para-selectivity. The para-substituted phenol gave monohalogenated product with good yield and ortho-selectivity. N-Heteroarenes such as indoles and imidazoles also gave monohalogenated products with high selectivity. Unlike the copper-catalyzed halogenation, the present method works well with electron-withdrawing group bearing phenols and gives comparatively better yields and selectivity. The Cu-Mn spinel catalyst is robust and reused three times under optimized conditions without any loss in catalytic activity. Nonphenolics did not undergo this transformation.     

离子液体/季铵盐辅助氯过氧化物酶促氧化合成聚酚

基于氯过氧化物酶(CPO)催化氧化苯酚衍生物单体,建立了一个聚酚的绿色合成体系.以对苯基苯酚、对甲基苯酚、4-乙基苯酚、对羟基肉桂酸、对异丙基苯酚和邻甲基苯酚等6种底物为考察对象,以聚合物的产率、聚合度及热稳定性为评价指标,研究了体系中引入离子液体(ILs)或季铵盐(QAS)以及底物结构和反应微环境等对聚合反应和聚合物性质的影响.结果表明,引入少量咪唑类ILs或QAS可有效提高产物收率,其中ILs/QAS的阳离子基团越大和疏水链越短,越有利于酶催化聚合反应的进行;而ILs/QAS添加量的影响则呈现"钟罩"型规律.同时,苯酚对位取代远比邻位取代有利于聚合反应进行;而对位取代基中烷基类给电子基团比芳香基取代更有优势,所得聚合物的聚合度和热稳定性相对增大,但随着取代基团的增大,其空间位阻不利于聚合物产率的提高;反应体系的p H应控制在弱酸性至近中性,以避免竞争性的副反应的发生;而氧化剂H_2O_2则需要采用间歇式加入以抑制瞬时过浓导致CPO活性中心卟啉环的氧化损伤.基于CPO的活性中心结构分析了聚合机理.     

Late-Stage Direct o-Alkenylation of Phenols by PdII-Catalyzed C−H Functionalization

o-Alkenylation of unprotected phenols has been developed by direct C−H functionalization catalyzed by Pd^II. This work features phenol group as a directing group and realizes highly site-selective C−H bond functionalization of phenols to achieve the corresponding products in moderate to excellent yields at 60 °C. The advantages of this reaction include unprecedented C−H functionalization using phenol as a directing group, high regioselectivity, good substrate scope, mild reaction conditions, and high efficiency. To the best of our knowledge, this is the first example of a regioselective C−H alkenylation of unprotected phenols utilizing phenolic hydroxyl group as a directing group. The alkenylation of unprotected tyrosine and intramolecular cyclization are also successfully carried out under this catalytic system in good yields. Furthermore, this novel method enables a late-stage modification of complex phenol-containing bioactive molecules toward a diversity-oriented drug discovery.     

Regioselective hydroxylation of phenols by simultaneous photochemical generation of phenol cation-radical and hydroxyl radical

Substituted phenols having pendant isoquinoline N-oxide were synthesized and their photochemical and luminiscent properties studied. Photolysis in an acid medium was found to yield the related photohydroxylation products, in a regioselective process, in addition to the isoquinoline deoxygenated precursor. Photoinduced electron transfer from the donor phenols to the protonated form of the first excited singlet state (S₁) of the pendant isoquinoline N-oxide acting as acceptor leads to a red-shifted emissive charge transfer (CT) state that is in fact a radical/cation-radical pair. Homolysis of the N-OH bond restores the aromatic isoquinoline nucleus and produces a hydroxyl radical that can couple to the required ring carbon in the phenol cation-radical to give the photohydroxylation products in a regioselective process controlled by the spin density of the phenol cation-radical. These photohydroxylation processes efficiently compete with the reported tendency to deprotonation in phenol cation-radicals. The photohydroxylation process by itself, and its regioselectivity, exclude a proton-coupled electron transfer mechanism or a consecutive electron transfer/deprotonation reaction. By contrast, the phenol cation-radical exists long enough to undergo the hydroxyl radical coupling reaction that leads to the photohydroxylation products.     

Regiocontrolled nitration of di(tert-butyl)phenols

The nitration of 2,4-di(tert-butyl)phenol and 2,6-di(tert-butyl)phenol is accompanied by oxidative processes, leading to products of the oxidative coupling of the starting di(tert-butyl)phenols. On the other hand, the corresponding nitrophenols are formed in quantitative yield in the substitutive nitration of 6-XCH₂- and 4-XCH₂-di(tert-butyl)phenols (X-OH, OR, NR₂).Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2381–2383, October, 1991.     

Unified mechanistic concept of electrophilic aromatic nitration: convergence of computational results and experimental data

The mechanism of electrophilic aromatic nitration was revisited. Based on the available experimental data and new high-level quantum chemical calculations, a modification of the previous reaction mechanism is proposed involving three separate intermediates on the potential energy diagram of the reaction. The first, originally considered an unoriented pi-complex or electron donor acceptor complex (EDA), involves high electrostatic and charge-transfer interactions between the nitronium ion and the pi-aromatics. It explains the observed low substrate selectivity in nitration with nitronium salts while maintaining high positional selectivity, as well as observed oxygen transfer reactions in the gas phase. The subsequent second intermediate originally considered an oriented "pi-complex" is now best represented by an intimate radical cation-molecule pair, C(6)H(6)(+)(*)()/NO(2), that is, a SET complex, indicative of single-electron transfer from the aromatic pi-system to NO(2)(+). Subsequently, it collapses to afford the final sigma-complex intermediate, that is, an arenium ion. The proposed three discrete intermediates in electrophilic aromatic nitration unify previous mechanistic proposals and also contribute to a better understanding of this fundamentally important reaction. The previously obtained ICR data of oxygen transfer from NO(2)(+) to the aromatic ring are also accommodated by the proposed mechanism. The most stable intermediate of this reaction on its potential energy surface is a complex between phenol and NO(+). The phenol.NO(+) complex decomposes affording C(6)H(6)O(+)(*)/PhOH(+) and NO, in agreement with the ICR results.     

Stereoselective and regioselective reaction of cyclic ortho esters with phenols

Cyclic ortho esters undergo stereoselective and regioselective reaction with phenols when treated with BF(3) x OEt(2) at low temperatures. Attack of the phenol on the ortho ester occurs at an open carbon para to electron-donating groups on the phenol ("C-addition") or at the phenolic hydroxyl group ("O-addition") depending on the nature of the cation formed from reaction of the ortho ester and BF(3) x OEt(2). Products resulting from O-addition undergo reversion to a mixture of starting phenol, C-addition product, and O-addition product if treated with BF(3) x OEt(2) at room temperature, but C-addition products are stable under the same conditions. X-ray structural analysis of the C-addition compound indicates that its stereochemistry is opposite to that observed in reaction of similar ortho esters with chloride from TMSCl. However, the stereochemistry of the reaction can be rationalized by the ability of the ortho ester to isomerize via an intermediate benzylic cation and examination of the preferred trajectory of attack of the nucleophile on the intermediate oxonium ion.     

反相微乳液中苯酚硝化反应选择性的研究

采用气相色谱内标法研究了苯酚在AOT/异辛烷/水、CTAB/正癸醇/异辛烷/水、DBSA/异辛烷/水3种反相微乳液中进行硝化反应的选择性;考察了表面活性剂种类、反应时间、反应温度以及反相微乳液的含水量等因素对反应选择性的影响.研究结果表明,苯酚在微乳液体系中的硝化反应具有明显的邻位选择性,阴离子表面活性剂DB-SA体系的邻位选择性最高,这与它同时具有微乳催化和酸催化作用有关.     

聚苯乙烯基偶氮聚合物的合成研究

改进了聚苯乙烯的硝化、还原、重氮化和偶合反应路线 (NRDC) ,使每步反应都得到很高的产率 ,并利用大分子重氮盐 (MDS)分别与苯胺、N 烃基苯胺和酚等三类化合物偶合 ,得到相应的聚苯乙烯基偶氮聚合物 .核磁共振分析结果证明了产物的高偶联率 .通过对大分子重氮盐热稳定性的研究 ,发现偶合反应之后需要一步加热反应以消除残余重氮基团 .还研究了这些聚合物的紫外 可见吸收光谱性质 ,氨 (胺 )基偶氮产物的水溶液表现出了明显的pH敏感性     

Efficient method for the direct preparation of aryl carboxylates from carboxylic acids using tosyl chloride under solvent-free conditions

A simple, clean and efficient solvent-free procedure for the preparation of aryl carboxylates is described from the direct reaction of carboxylic acids and phenols, in the presence of 1-methylimidazole as base and tosyl chloride (TsCl) as coupling agent. This method can be easily applied for different substituted phenols and carboxylic acids. It can also be applied for the selective acylation when other functional group such as hydroxyl is present on phenol ring.     

固载型季铵盐离子液体催化合成环状碳酸酯:烷基链长及羟基的影响

CO2是造成温室效应的主要原因,同时又是地球上储量最为丰富的可再生C1能源.因此,CO2资源化受到了广泛关注.CO2与环氧化物反应可合成环状碳酸酯,后者广泛用作极性溶剂、锂离子电池的电解液和聚碳酸酯中间体等.但是,由于CO2的化学惰性,其反应需要高活性的催化剂.近年来,碱性金属、金属配合物及离子液体等均相催化剂被用于催化CO2与环氧化物加成反应.其中,离子液体具有高热稳定性、低挥发性和结构可调性,得到了广泛研究.季铵盐、咪唑盐和季鏻盐等离子液体已经被证实具有较高的催化活性.然而,均相催化剂回收困难,而且产物需要进一步纯化.将离子液体固载化制备成非均相催化剂,可以实现简单的固/液分离.聚合物、SiO2、SBA-15、氧化石墨烯和羧甲基纤维素等固载化催化剂已经广泛用于CO2和环氧化物的环加成反应.虽然非均相催化剂显示了潜在的优势,但是催化活性较低的问题仍然亟待解决,尤其是在较温和的反应条件下.因此,通过催化剂分子结构设计以提高催化性能,成为目前的研究热点.本文提出在催化活性基团和载体之间引入长烷基链,增加催化活性位点与反应物的接触面积,同时引入助催化的羟基,通过长链与羟基的协同作用,提高非均相催化剂活性.本文合成了羟基功能化长柔性链季铵化聚苯乙烯微球非均相催化剂([AHTAPC-PS]X,X=Cl,Br,I),用于催化CO2与环氧化物的环加成反应,并与不含羟基的长烷基链季铵盐离子液体非均相催化剂([TAPB-PS]Br)及短烷基链季铵盐离子液体非均相催化剂([TMA-PS]X)的催化性能进行了对比.考察了固载后的离子液体烷基链长及侧链羟基对催化性能的影响,并通过实验和密度泛函理论计算研究了催化机理.红外光谱、扫描电镜和能量散射谱结果充分证明了季铵盐非均相催化剂的成功合成;热重测试表明,此类催化剂具有可以满足反应需求的热稳定性.密度泛函理论计算结果显示,与短烷基链非均相催化剂相比,长烷基链非均相催化剂的阴离子负电性更强,同时羟基与环氧化合物的氧原子之间存在强的氢键作用.羟基形成的氢键可以增加环氧化物的C–O键长,同时强负电的阴离子更加容易攻击β-碳原子,促进环氧化物开环.另外,长烷基链结构使得卤素阴离子具有与反应物更大的接触范围,因此提高了反应活性.当采用短烷基链季铵盐非均相催化剂时,环氧丙烷(PO)与CO2环加成反应生成碳酸丙烯酯(PC)的产率仅为70.9%,而采用长烷基链季铵盐非均相催化剂时产率可达91.4%(135°C,1.5MPa,3h),进一步加入助催化的羟基,则PC产率可提高到98.5%.此外,含羟基的长烷基季铵盐非均相催化剂在温和条件下也具有较高的催化活性(100°C,1.5 MPa,3 h,PC产率78.4%),该催化剂同时具有较高的循环稳定性(10次循环后,PC产率≥96%,选择性≥99%).综上所述,该催化剂具有优异的综合性能,展现了良好的工业应用前景.     

Rapid and efficient chemoselective and multiple sulfations of phenols using sulfuryl imidazolium salts

Phenolic sulfates protected with a trichloroethyl or trifluoroethyl group were rapidly and efficiently obtained by reacting phenols with sulfuryl imidazolium salts in the presence of DBU. Phenolic hydroxyl groups could be sulfated in good yield in the presence of aliphatic hydroxyl groups and multiple sulfations were also readily achieved.     

Kinetics of the Anaerobic Reaction of para‐Substituted Phenols with Nitrogen Dioxide

para‐Substituted phenols in aqueous solution under anaerobic conditions readily react with nitrogen dioxide (NO₂^●) over a wide range of experimental conditions. The rate and rate law of the process were dependent on phenol concentration and solution pH. The kinetic order in phenol changed from one (low concentration) to zero (high concentration), a result attributable to total NO₂^● capture. Initial consumption rate (r ₀) of phenols versus pH plots showed parabolic behavior with a minimum rate at pH ca. 5. On the other hand, the maximum rate took place at high pH (pH>10) and involved the protonated phenols. The reaction rate of para‐substituted phenols with NO₂^● correlated with the bond dissociation energy and with Hammett's parameter. Based on such results and also supported by analysis of products carried out by HPLC‐MS/MS, our data conclusively show that, in spite of the fast acid–base interchanges of phenols and the interconversion of the different nitrogen oxides, the mechanisms of phenols nitration mediated by NO₂^● or HONO are clearly different.     

由O-苄基异脲合成苄基醚的新方法

以BF3·Et2O为催化剂、O-苄基异脲和醇(酚)为反应原料,在中性、温和的条件下合成苄基醚,可得产率从57.5％到91％.这为有机合成中用苄基醚保护醇、酚羟基提供了一条新途径.     

1-oxo-2,2,6,6-tetramethyl-4-chloropiperidinium perchlorate. A new facile oxidant for phenol coupling

The title compound (1) oxidizes 2,6-di-tert-butylphenol (2), 2,6-di-tert-butyl-4-methylphenol (3), 2,6-di-tert-butyl-4-(dipnenylmethyl)phenol (4), and p-naphthol (5), to quinones in good yield under mild conditions in acetonitrile. For unsubstituted phenols the reaction takes place in two ways, phenol (6) is oxidized to quinhydrone (7), while the oxidation products of the phenols, α-naphthol, catechol and 2,4-dihydroxyl-naphthol were only polymers.     

The aqueous phase nitration of phenol and benzoic acid studied through flow-gated capillary electrophoresis

The aqueous phase nitration of benzoic acid and phenol was investigated via on-line capillary electrophoresis (CE). The presence of nitrated benzoic acid and phenol was supported through appearance of corresponding molecular ion peaks in ESI-MS measurements, and speciation of the nitrated isomers is achieved via the on-line CE method. The nitrated isomers produced in both reactions were successfully separated in <4?min by addition of 15?mM β-cyclodextrin to the electrophoresis buffer. Sequential separations (on-line analysis) allowed the reaction kinetics to be described. For benzoic acid, reaction yields were low (2–3%) however, results suggest both 3- and 2-nitrobenzoic acid form in a 1–1.4 concentration ratio. In addition, 3-hydroxybenzoic acid also forms in significant quantity under our reaction conditions. For the nitration of phenol, the reaction occurred more rapidly with observed yields between ≈10–30% for individual isomers. The yield of 2-nitrophenol was higher than 4-nitrophenol by a ratio of ≈?1.7–2, but 3-nitrophenol was not detected. For both reactions, nitrated and hydroxylated aromatics were the major products and formation of higher molecular weight oligomers was not observed.     

Vitamin E chemistry. Nitration of non-alpha-tocopherols: products and mechanistic considerations

In contrast to the alpha-form permethylated at the aromatic ring, non-alpha-tocopherols possess free aromatic ring positions which enable them to act as potent scavengers of electrophiles in vivo and in vitro. In preparation of enzymatic studies involving peroxynitrite and other nitrating systems, the behavior of non-alpha-tocopherols under nitration conditions was studied. The nitration products of beta-, gamma-, and delta-tocopherol were identified, comprehensively analytically characterized, and their structure was supported by X-ray crystal structure analysis on truncated model compounds. Even under more drastic nitration conditions, no erosion of the stereochemistry at 2-C occurred. The nitrosation of gamma-tocopherol and delta-tocopherol was re-examined, showing the slow oxidation of the initial nitroso products to the corresponding nitro derivatives by air to be superimposed by a fast equilibrium with the tautomeric ortho-quinone monoxime, which only in the case of gamma-tocopherol released hydroxyl amine at elevated temperatures to afford the stable ortho-quinone. Mononitration of delta-tocopherol selectively proceeded at position 5. This selectivity can be explained by the theory of strain-induced bond localization (SIBL) to the quinoid nitration intermediates. Bisnitration was only insignificantly disfavored by the first nitro group, so that under normal nitration conditions offering an excess of nitrating species only the bisnitration product was found.     

tert-Buyldiphenylsilylethyl ("TBDPSE"): a practical protecting group for phenols

[reaction: see text] A new protection group for phenols, the 2-(tert-butyldiphenylsilyl)ethyl (TBDPSE) group, has been prepared and investigated. Protection of a variety of substituted phenols proceeds in good to excellent yield. The group is stable to mild acid, base, hydrogenolysis conditions, and lithium/halogen exchange on the protected phenol. Removal is achieved with strong acid or standard fluoride treatment.     

Reaction of elemental phosphorus with phenols

Conclusions The composition and yield of the products formed upon the reaction of elemental phosphorus with phenols depends on the acidity of the phenol and the nature of the ring substituent. The phenol pK_a range, in which the reaction of elemental phosphorus with phenols is possible, is 9–11.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2632–2634, November, 1988.