负载型杂多酸催化下N2O5对氯苯的选择性硝化研究

使用负载型杂多酸为催化剂,N2O5为硝化剂的新型硝化体系,对氯苯的硝化反应进行研究。文章分别考察了杂多酸类型、载体种类、杂多酸负载量及催化剂循环使用次数等因素对硝化反应的影响。结果证明,N2O5硝化反应属于酸催化反应,负载型杂多酸能显著提高N2O5的硝化能力;催化剂回收后可直接重复使用,催化活性没有明显的降低。在优化条件下,氯苯硝化反应得率为26%,对位选择性达到68.8%,表明N2O5是一种具有应用前景的硝化试剂,可取代传统的硝硫混酸硝化法,减少废酸处理,符合绿色环保要求。     

负载型杂多酸催化下N2O5对氯苯的选择性硝化

使用负载型杂多酸为催化剂,N2O5为硝化剂的新型硝化体系,对氯苯的硝化反应进行研究. 分别考察了杂多酸类型、载体种类、杂多酸负载量及催化剂循环使用次数等因素对硝化反应的影响. 结果表明,N2O5硝化反应属于酸催化反应,负载型杂多酸能显著提高N2O5的硝化能力;催化剂回收后可直接重复使用,催化活性没有明显的降低. 在优化条件下,氯苯硝化反应得率为26%,对位选择性达68.8%. 结果表明,N2O5是一种具有应用前景的硝化试剂,可取代传统的硝硫混酸硝化法,减少废酸处理,符合绿色环保要求.     

十二烷基苯的硝化选择性

借助气相色谱发现正十二烷基苯在硝硫混酸和硝磷混酸中硝化时，一硝化产物中对位异构体可达６０％，较在硝酸乙酸酐中硝化时的对位选择性高１０％，利用１ＨＮＭＲ测定了工业十二烷基苯和正十二烷基苯在高浓度硫酸（９８％）的硝硫混酸中的硝化选择性，发现前者的硝化中对位异构体的高达８０％。     

硫酸氢钠催化下甲苯的硝化

研究了硫酸氢钠催化下甲苯用硝酸的硝化.结果表明,在醋酐存在条件下,以CCl4为溶剂,以质量分数为95%的硝酸为硝化剂,反应温度控制在45℃,反应进行60 min,选用硫酸氢钠催化剂.对甲苯表现出了强的区域选择性,甲苯硝化产物邻对位比达1.09,较硝酸硫酸混酸的1.67显著降低.硝化产物收率达到99.9%.催化剂可循环使用5次,催化活性基本不变,是一种极具工业化开发价值的硝化反应催化剂.     

负载型杂多酸催化下N2O5对甲苯的选择性硝化

用负载型杂多酸为催化剂,N2O5为硝化剂的新型硝化体系,对甲苯的硝化反应进行研究. 分别考察了杂多酸类型、载体种类、杂多酸负载量及催化剂循环使用次数等因素对硝化反应的影响. 结果证明,负载型杂多酸能显著提高N2O5的硝化能力;催化剂回收后可直接重复使用,甲苯硝化反应得率为34%,对位选择性达到58.9%,表明N2O5是一种具有应用前景的硝化试剂.     

一硝基氯苯的区域选择性合成研究(Ⅱ)NO2硝化

催化硝化;固体强酸;O3活化;一硝基氯苯的区域选择性合成研究(Ⅱ)NO2硝化     

2-甲基-N-[4-硝基-3-三氟(甲基)苯基]丙酰胺的改进合成

以3－三氟里基苯为原料,在吸酸剂碳酸氢钠作用下与2－甲基丙酰氯反应得到2－甲基－N－[4－硝基－3－三氟（甲基）苯基]丙酰胺,再进行混酸硝化得到目标化合物。     

邻氯甲苯直接硝化法合成6-氯-3-氨基甲苯-4-磺酸

邻氯甲苯混酸硝化合成6-氯-3-氨基甲苯-4-磺酸(CLT酸)因其产率低及选择性差而未能实现工业生产,本文对该工艺进行了改进,采用酸性β沸石和乙酰硝酸酯作为催化剂和硝化剂,提高了硝化选择性和收率,分别为72％和97％;并改进了还原、异构体分离和磺化操作;CLT酸总收率提高到61％.     

单取代芳烃的硝化

以甲苯、乙苯、异丙苯、叔丁基苯、氟苯等为硝化底物,通过混酸硝化得到这些单取代芳烃转化率最大时的混酸硝化强度φ。 运用密度泛涵理论,在B3LYP/6-311G**水平上优化了9种单元芳烃的几何构型,计算苯环上C原子电荷分布。 讨论了9种取代基的定位效应,以苯环取代基以外环上C原子总净电荷QRΣC(2~6)表示单取代苯的硝化反应活性与硝化强度φ之间的关系。 实验结果表明,烷基苯、卤苯、硝基苯的硝化反应活性与其混酸硝化转化率达最大时的混酸硝化强度φ呈良好的线性关系。     

蛋白质酪氨酸硝化的研究

蛋白质酪氨酸硝基化是一种重要的蛋白质翻译后修饰,与多种病症相关。经由过氧亚硝酸根(ONOO-)和NO2-/H2O2/血红素过氧化物酶体系是促使蛋白质硝化最主要的两种途径,其反应为自由基机理。本文对体内蛋白质硝基化的途径、机制及其生物学意义作了综述,指出蛋白质的硝化具有选择性,特定酪氨酸残基发生硝化能够改变蛋白质的结构和功能,影响其免疫应答和可能涉及的信号转导过程,从而具有重要的生物学意义。     

15N CIDNP investigations of the peroxynitric acid nitration of L-tyrosine and of related compounds

Peroxynitric acid (O2NOOH) nitrates L-tyrosine and related compounds at pH 2-5. During reaction with O2(15)NOOH in the probe of a 15N NMR spectrometer, the NMR signals of the nitration products of L-tyrosine, N-acetyl-L-tyrosine, 4-fluorophenol and 4-methoxyphenylacetic acid appear in emission indicating a nitration via free radicals. Nuclear polarizations are built up in radical pairs [15NO2* , PhO*]F or [15NO2* , ArH*+]F formed by diffusive encounters of 15NO2 with phenoxyl-type radicals PhO or with aromatic radical cations ArH*+. Quantitative 15N CIDNP investigations with N-acetyl-L-tyrosine and 4-fluorophenol show that the radical-dependent nitration is the only reaction pathway. During the nitration reaction, the 15N NMR signal of 15NO3- also appears in emission. This is explained by singlet-triplet transitions in radical pairs [15NO2* , 15NO3*]S generated by electron transfer between O2(15)NOOH and H15NO2 formed as a reaction intermediate. During reaction of peroxynitric acid with ascorbic acid, 15N CIDNP is again observed in the 15N NMR signal of 15NO3- showing that ascorbic acid is oxidized by free radicals. In contrast to this, O2(15)NOOH reacts with glutathione and cysteine without the appearance of 15N CIDNP, indicating a direct oxidation without participation of free radicals.     

Easy oxidation and nitration of human myoglobin by nitrite and hydrogen peroxide

The modification of human myoglobin (HMb) by reaction with nitrite and hydrogen peroxide has been investigated. This reaction is important because NO(2) (-) and H(2)O(2) are formed in vivo under conditions of oxidative and nitrative stress, where protein derivatization has been often observed. The abundance of HMb in tissues and in the heart makes it a potential source and target of reactive species generated in the body. The oxidant and nitrating species produced by HMb/H(2)O(2)/NO(2) (-) are nitrogen dioxide and peroxynitrite, which can react with exogenous substrates and endogenous protein residues. Tandem mass analysis of HMb modified by stoichiometric amounts of H(2)O(2) and NO(2) (-) indicated the presence of two endogenous derivatizations: oxidation of C110 to sulfinic acid (76 %) and nitration of Y103 to 3-nitrotyrosine (44 %). When higher concentrations of NO(2) (-) and H(2)O(2) were used, nitration of Y146 and of the heme were also observed. The two-dimensional gel-electrophoretic analysis of the modified HMbs showed spots more acidic than that of wild-type HMb, a result in agreement with the formation of sulfinic acid and nitrotyrosine residues. By contrast, the reaction showed no evidence for the formation of protein homodimers, as observed in the reaction of HMb with H(2)O(2) alone. Both HMb and the modified HMb are active in the H(2)O(2)/NO(2) (-)-dependent nitration of exogenous phenols. Their catalytic activity is quite similar and the endogenous modifications of HMb therefore have little effect on the reactivity of the protein intermediates.     

Aromatic hydrocarbon nitration under tropospheric and combustion conditions. A theoretical mechanistic study

The viability of some nitration pathways is explored for benzene (B), naphthalene (N), and in part pyrene (P). In principle, functionalization can either take place by direct nitration (NO2 or N2O5 attack) or be initiated by more reactive species, as the nitrate and hydroxyl radicals. The direct attack of the NO2 radical on B and N, followed by abstraction of the H geminal to the nitro group (most likely accomplished by 3O2) could yield the final nitro-derivatives. Nevertheless, the initial step (NO2 attack) involves significant free energy barriers. N2O5 proves to be an even worst nitrating agent. These results rule out direct nitration at room temperature. Instead, NO3 and, even more easily, HO can form pi-delocalized nitroxy- or hydroxycyclohexadienyl radicals. A subsequent NO2 attack can produce several regio- and diastereoisomers of nitroxy-nitro or hydroxy-nitro cyclohexadienes. In this respect, the competition between NO2 and O2 is considered: the rate ratios are such to indicate that the NO3 and HO initiated pathways are the major source of nitroarenes. Finally, if the two substituents are 1,2-trans, either a HNO3 or a H2O concerted elimination can give the nitro-derivatives. Whereas HNO3 elimination is feasible, H2O elimination presents, by contrast, a high barrier. Under combustion conditions the NO2 direct nitration pathway is more feasible, but remains a minor channel.     

Electrophilic nitration of aromatics in ionic liquid solvents.

Potential utility of a series of 1-ethyl-3-methylimidazolium salts [emim][X] with X = OTf-, CF3COO-, and NO3- as well as [HNEtPri2][CF3COO] (protonated Hünig's base) ionic liquids were explored as solvent for electrophilic nitration of aromatics using a variety of nitrating systems, namely NH4NO3/TFAA, isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH, Cu(NO3)/TFAA, and AgNO3/Tf2O. Among these, NH4NO3/TFAA (with [emim][CF3COO], [emim][NO3]) and isoamyl nitrate/BF3.Et2O, isoamyl nitrate/TfOH (with [emim][OTf]) provided the best overall systems both in terms of nitration efficiency and recycling/reuse of the ionic liquids. For [NO2][BF4] nitration, the commonly used ionic liquids [emim][AlCl4] and [emim][Al2Cl7] are unsuitable, as counterion exchange and arene nitration compete. [Emim][BF4] is ring nitrated with [NO2][BF4] producing [NO2-emim][BF4] salt, which is of limited utility due to its increased viscosity. Nitration in ionic liquids is surveyed using a host of aromatic substrates with varied reactivities. The preparative scope of the ionic liquids was also extended. Counterion dependency of the NMR spectra of the [emim][X] liquids can be used to gauge counterion exchange (metathesis) during nitration. Ionic liquid nitration is a useful alternative to classical nitration routes due to easier product isolation and recovery of the ionic liquid solvent, and because it avoids problems associated with neutralization of large quantities of strong acid.     

Metmyoglobin-catalyzed exogenous and endogenous tyrosine nitration by nitrite and hydrogen peroxide

Metmyoglobin catalyzes the nitration of various phenolic compounds in the presence of nitrite and hydrogen peroxide. The reaction rate depends on the reactant concentrations and shows saturation behavior. Two competing paths are responsible for the reaction. In the first, myoglobin reacts according to a peroxidase-like cycle forming two active intermediates, which can induce one-electron oxidation of the substrates. The MbFe(IV)==O intermediate oxidizes nitrite to nitrogen dioxide, which, after reaction with the phenol or with a phenoxy radical, yields the nitrophenol. In the second mechanism, hydrogen peroxide reacts with iron-bound nitrite to produce an active nitrating species, which we assume to be a protein-bound peroxynitrite species, MbFe(III)--N(O)OO. The high nitrating power of the active species is shown by the fact that the catalytic rate constant is essentially independent of the redox properties of the phenol. The occurrence of one or other of these mechanisms depends on the nitrite concentration: at low [NO(2) (-)] the nitrating agent is nitrogen dioxide, whereas at high [NO(2) (-)] the peroxynitrite path is dominant. The myoglobin derivative that accumulates during turnover depends on the mechanism. When the path involving NO(2) (.) is dominant, the spectrum of the MbFe(IV)==O intermediate is observed. At high nitrite concentration, the Soret band appears at 416 nm, which we attribute to an iron-peroxynitrite species. The metMb/NO(2) (-)/H(2)O(2) system competitively nitrates the heme and the endogenous tyrosine at position 146 of the protein. Phenolic substrates protect Tyr146 from nitration by scavenging the active nitrating species. The exposed Tyr103 residue is not nitrated under the same conditions.     

Highly efficient nitration of phenolic compounds in solid phase or solution using Bi(NO3)3.5H2O as nitrating reagent

[reaction: see text] Bi(NO(3))(3).5H(2)O was used as an efficient nitrating reagent in the nitration of phenolic compounds to give nitrated phenols in good to high yields. The nitration reaction proceeded smoothly by grinding 1 equiv of phenol, 2-methylphenol, 4-methylphenol, or 4-chlorophenol and Bi(NO(3))(3).5H(2)O, and the nitration of other phenolic compounds could be performed in acetone at ambient temperature (22-30 degrees C).     

Mn对异丁烯选择氧化制甲基丙烯醛Mo-Bi-Fe-Co-Cs-K复合氧化物催化剂的促进作用及其机理

采用共沉淀法制备了系列异丁烯选择氧化制甲基丙烯醛（MAL）Mo-Bi基复合氧化物催化剂,在常压固定床流动反应体系上考察了Mn助剂及其添加方式对催化剂性能的影响,并结合对相关催化剂物相结构的表征,探讨了Mn的作用机理.研究表明,以Mn（NO3）2为前驱体将Mn引入Mo-Bi-Fe-Co-Cs-K复合氧化物可显著提高催化剂...     

Structural investigation of Pd(II) in concentrated nitric and perchloric acid solutions by XAFS

XAFS spectra of palladium(II) in concentrated HNO3/HClO4 acid mixtures have been recorded and analyzed. Structural parameters of the Pd(H2O)4(2+) complex and the mixed nitric Pd(NO3)2(H2O)2 complex, for the first time, were determined by the XAFS method. For pure 5 M HClO4 and for mixtures (0-0.3 M HNO3), the XAFS spectra of the 0.02 M Pd solutions are indeed very similar and originated from four Pd-O(w) equivalent distances. For the Pd(H2O)4(2+) square-planar aqua ion in strong perchloric acid, the use of an FEFF6 theoretical approach led to a first-shell Pd-O(w) distance of 2.00 (1) A and a Debye-Waller (DW) factor of sigma2 = 0.0030 (3) A2. Four water molecules are tightly bound to the Pd2+ ion in the equatorial plane, while two (or one) axial water molecules are weakly bound to the metal ion at 2.5 A with a DW factor of 0.015 (5) A2. For highly concentrated mixtures (4-6 M HNO3) and for pure concentrated (4-6 M) nitric acid as well as for crystalline powder Pd(NO3)2(H2O)2, the XAFS spectra are very similar and are determined by the mixed nitric complex Pd(NO3)2(H2O)2: four Pd-O near-equivalent distances of 2.01 (1) A from two H2O and two NO3 molecules with a total DW factor of sigma2 = 0.0037 (3) A2. Moreover, two Pd---N distances of 2.8-2.9 A were determined in the second coordination shell. Finally, for intermediate mixtures (1-3 M HNO3 in 5 M HClO4), the XAFS spectra are a superposition of the XAFS of Pd(H2O)4(2+) and Pd(NO3)2(H2O)2 complexes. The mean ligand number NO3(-) around Pd2+ has been calculated, and the XAFS results at pH close to zero confirm the spectrophotometric results previously published.     

Theoretical investigation of nitration and nitrosation of dimethylamine by N2O4

Reactive nitrogen oxygen species (RNOS) contribute to the deleterious effects attributed to reacting with biomolecules. The mechanisms of the nitration and nitrosation of dimethylamine (DMA), which is the simplest secondary amine by N2O4, a member of RNOS, have been investigated at the CBS-QB3 level of theory. The nitration and nitrosation proceed via different pathways. The nitration of DMA follows three pathways. The first is the abstraction of the hydrogen atom of the amino group of DMA by the NO2 radical followed by a recombination reaction of the resulting aminyl radical with another NO2 radical. The second is DMA directly reacting with symmetrical O2NNO2 leading to dimethylnitramine via a concerted and a stepwise mechanism. The third is the reaction of DMA with asymmetrical ONONO2. By computation, the main pathway for the formation of dimethylnitramine in the gas phase is by DMA directly reacting with asymmetrical ONONO2. As to the nitrosation, a concerted mechanism for the reaction of DMA with asymmetrical ONONO2 plays a major role in nitrosodimethylamine (NDMA) formation. In addition, the solvent effect on these nitration and nitrosation reactions has been also studied by using the implicit polarizable continuum model. Two major pathways of the formation of dimethylnitramine in water were found, and they are the radical process involving NO2 and the concerted mechanism starting from symmetrical O2NNO2. The result of the nitrosation of DMA in water is consistent with that in the gas phase. Comparison of the energy barriers of each mechanism leads to the conclusion that the nitrosation is more favorable than the nitration in the reaction of DMA with N2O4. This conclusion is in good agreement with the experimental results. The results obtained here will help elucidate the mechanism of the lesions of biomolecules by RNOS.