钝化芳环的硝化研究进展*

芳香族化合物的硝化反应是工业生产中重要的单元反应,钝化芳环的硝化反应在医药、农药、染料和炸药合成中有重要地位。本文从硝化试剂角度综述了近年来钝化芳环的硝化反应的进展,包括硝酸盐/硫酸、硝酸酯、硝酸、氮氧化物等硝化方法。简要评述了这些方法的特点,并展望了硝化方法的研究方向。其中,硝酸盐/硫酸体系具有较强的硝化能力,对于钝化芳环,可以在温和条件下以高收率得到硝化产物,在实验室制备或工业应用中具有较高的应用价值;其他硝化方法由于各种原因暂时不能对钝化程度较高的芳环进行硝化,还需进一步研究具有较高活性的硝化体系。     

吡啶的亲电取代反应

介绍了吡啶的硝化、磺化、卤代等亲电取代反应，并对吡啶难以进行亲电取代反应的原因进行了分析讨论。     

苯硝化反应中电子转移反应重组能的计算

提出了重组能的量子化学算法,在用CISD/6-31G基组水平上,得到苯硝化反应中反应物及过渡态的结构.并计算了各自交换电子转移反应以及交叉电子转移反应的重组能,同实验重组能进行了比较.计算用了Gaussian 94程序.从重组能的角度分析了苯硝化反应.结果表明,对于NO2++NO2→NO2+NO2+的自交换电子转移反应,重组能较大,结论为: 在芳烃硝化反应中,存在以NO2+为氧化剂的电子转移步骤的可能性很小,而从动力学的角度上,用NO+作反应的氧化剂更有可能.     

Gaussian量子化学模拟对芳烃硝化机理的探索

芳烃硝化反应是一类重要的亲电取代反应。本文综述了运用Gaussian量子化学模拟方法对芳烃硝化机理探索的进展，提倡在大学化学教学中引入Gaussian，以提高大学化学教学质量。     

铜催化的芳环C—H键直接芳基化反应研究进展

铜催化的芳环C—H键直接芳基化反应已成为一种合成联芳烃化合物的重要手段,近年来一直是有机化学和催化化学的研究热点和难点之一.按照参与反应的底物或成键模式的不同对近年来铜催化的芳环C—H键直接芳基化反应的研究进展进行了综述.     

硅-芳键的断裂反应

利用等摩尔竞争法我们研究了五种芳基三甲基硅烷与氯化氢的非均相断裂反应。用气体色谱法对各竞争反应产物进行定量分析,求出各断裂产物的相对性产率,结果表明其活性顺序是与相应的均相断裂反应相一致的。     

硫醚中碳硫键室温选择性断裂反应的研究

本文研究了在四氟硼酸银存在下, 硫醚与碘甲烷室温下发生碳硫键选择性断裂反应。研究结果表明: 只有当二苄基硫醚的苯环对位连有强的供电子基团甲氧基时, 方可发生碳硫键的断裂。提出了一个离子型反应机理且碳硫键的断裂分三步完成。首先, 硫醚与甲基化试剂反应生成甲基锍盐; 继而, 此锍离子离解成由苄基碳正离子和硫醚组成的离子-偶极集合物; 最后, 甲基化试剂再进攻集合物中的硫醚, 从而导致碳硫键的断裂。     

己内酰胺对甲基苯磺酸离子液体中甲苯的选择性硝化反应

制备了一种低毒性的新型Brφnsted酸性离子液体己内酰胺对甲基苯磺酸([CP]PTSA)作为催化剂和溶剂,用于催化甲苯与等摩尔的体积分数为67%HNO3的硝化反应,用核磁共振、红外光谱对[CP]PTSA的结构进行了表征。考察了不同的反应温度、反应时间及催化剂用量等因素对甲苯硝化反应的产率和对位选择性的影响。得出最佳反应条件为:温度55℃,时间24h,离子液体用量占甲苯摩尔分数的20%,产物硝基甲苯中邻与对位异构体质量比为1.2,较硝-硫混酸硝化的相应比值(1.6)显著降低,硝基甲苯的产率达37.1%。离子液体重复使用4次仍表现出较好的催化活性及对位选择性。用质谱分析对回收的离子液体的结构进行了表征。结果表明,该离子液体的结构稳定。     

一系列烷基对二烷氧基苯在不同硝化体系中反应的研究

２－烷基－１，４－二甲氧基苯１ａ－ｄ（烷基为ＣＨ３，ＣＨ３ＣＨ２，ＰｈＣＨ２，（ＣＨ３）３Ｃ）分别在ＨＮＯ３－ＨＯＡｃ和ＮＨ４ＮＯ３－ＨＯＡｃ中反应后生成占绝对优势的硝化产物２－烷基－５－硝基－１，４－二甲氧基苯４ａ－ｄ，而２－烷基－５－叔丁基－１，４－二甲氧基苯２ａ－ｄ及２，５－二叔丁基－１，４－二苄氧基苯３在上述二种硝化体系中的反应在很大程度上取决于所用的硝化体系的性质及反应物的结构。对上述反     

An Experimentally Established Key Intermediate in Benzene Nitration with Mixed Acid

Experimental evidence is reported for the first intermediate in the classic S_EAr reaction of benzene nitration with mixed acid. The UV/Vis spectroscopic investigation of the reaction showed an intense absorption at 320 nm (appearing as a band shoulder) arising from a reaction intermediate. Our theoretical modeling shows that the interaction between the two principal reactants with solvent (H₂SO₄) molecules significantly affects the structure of the initial complex. In this complex, a larger distance between the aromatic ring and nitronium ion precludes the possibility for electronic charge transfer from the benzene π‐system to the electrophile. The computational modeling of the potential energy surface reveals that the reaction favors a stepwise mechanism with intermediate formation of π‐ and σ‐ (arenium ion) complexes.     

Nitration of Some Aromatic Compounds by Sodium Nitrate in the Presence of Benzyltriphenylphosphonium Peroxodisulfate

A simple, mild, and regioselective method for the nitration of some aromatic compounds using sodium nitrate in the presence of benzyltriphenylphosphonium peroxodisulfate in acetonitrile as solvent is reported. Mild reaction conditions and good to excellent yields of the products are the noteworthy advantages of the method.     

2-Polyfluoroalkylchromones. 5. Nitration and chlorination of 2-trifluoromethylchromones

Electrophilic nitration of 2-trifluoromethylchromone and its 6- and 7-methoxy derivatives affords 6-, 5-, and 8-nitro derivatives, respectively, while 5,7-dimethyl-2-trifluoromethylchromone yields a 6,8-dinitro derivative. Radical chlorination results in 3-chloro derivatives.     

Nitration of Porphyrin Systems: A Toolbox of Synthetic Methods

This review addresses nitration reactions of porphyrin derivatives. Simple porphyrins modifications afford valuable intermediates in this area of chemistry. They are useful materials for further transformations, as the NO₂ group introduced into parent porphyrin system increases its electrophilic character, thus allowing a broad spectrum of subsequent reactions, e. g. reduction of NO₂ to NH₂, subsequent diazotisation, nucleophilic substitution of hydrogen (in ortho-position to NO₂), a variety of cyclizations, etc. Such reactions are often utilized in the first steps of the designed syntheses, leading to attractive and useful target porphyrin molecules. This approach (via nitro-derivatives) allows synthesizing numerous porphyrin-like compounds of a high degree of complexity, and has thus become one of the methods choice. The substitution by NO₂ group can take place at all positions of the porphyrin systems: four meso-positions (5, 10, 15, 20) and eight positions β (2, 3, 7, 8, 12, 13, 17, 18). The third possibility includes the nitration in meso-aryl rings attached to positions 5, 10, 15, and 20. The latter derivatives (meso-aryl substituted ones) are a large, well-known group of synthetic porphyrins. The nitration reactions described herein follow three various mechanisms: (a) radical, (b) via π-cation radicals and π-dications, and (c) electrophilic. All the above cases are discussed in detail. According to our knowledge, this is the first such systematic account concerning these reactions.     

Mild and Efficient Nitration of Aromatic Compounds Mediated by Transition-Metal Complexes

Aromatic compounds were efficiently nitrated under facile reaction conditions by employing 69% nitric acid catalyzed by transition-metal complexes such as [Co(NH₃)₅Cl]Cl₂, [Cu(NH₃)₄]SO₄, Mn(acac)₃, [Ni(NH₃)₆]Cl₂, [Ni(en)₃]S₂O₃, and Hg[Co(SCN)₄]. The reaction was completed smoothly at room temperature and afforded corresponding mono-nitro derivatives in quantitative yield. This new method offers efficient and facile regioselective mononitration of aromatic compounds.

Nitration of Benzo Crown Ethers with Potassium Nitrate in Polyphosphoric Acid

A general method for the nitration of benzo crown ethers with potassium nitrate in polyphosphoric acid has been developed. Mono- and dinitro derivatives of benzo-12-crown-4, benzo-15-crown-5, dibenzo-18-crown-6, and dibenzo-24-crown-8 have been prepared. The role of complex formation in the regioselective tendency for the nitration of dibenzo-18-crown-6 has been demonstrated.     

Nitration of Aromatic Hydrocarbons and Halobenzenes Using NOx Catalyzed by Solid Acid Catalysts

The nitration of aromatics using zeolite as a solid inorganic catalyst and nitric oxides as nitrating agents is a relatively clean process for aromatic nitration.     

Nitration of tert-butyloxycarbonylated aniline and 1,3,5-triaminobenzene by acetyl nitrate

Acetyl nitrate was found to be an effective reagent for aromatic mono- and dinitration of Boc-protected aminobenzenes. The method was used in a new synthesis of 1,3,5-triamino-2,4-dinitrobenzene in two steps with 63% yield.