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wj621798

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Selective catalytic oxidation of toluene by molecular oxygen to benzaldehyde, benzyl alcohol and benzoic acid is an important transformation in chemical industry. However, improving the conversion of toluene and selectivity of value-added intermediates remains a challenge . The SINA process is a very important industrial process for preparation of caprolactam, Among them, liquid-phase oxidation of toluene is catalyzed by cobaltous salts at 165℃and 1.0 MPa with toluene conversion of 14–15 % and benzoic acid selectivity of 92–93 %, but only small amounts of benzaldehyde and benzyl alcohol are obtained as by-products. Benzaldehyde and benzyl alcohol are essential intermediates in the manufacture of various chemicals, such as pharmaceuticals, food stuff, dyes, perfume, and resins. Currently, benzaldehyde and benzyl alcohol are produced mainly by hydrolysis of benzal chloride [5, 6]. However, the above process inevitably produces a trace amount of chlorine, and thus, its use is prohibited in the pharmaceuticals and food stuff industries. For this reason, much attention has been paid to find outfind out new eco-friendly methods for production of benzaldehyde and benzyl alcohol via controlled toluene oxidation with molecular oxygen. Moreover, benzaldehyde and benzyl alcohol are more susceptible to secondary oxidation to benzoic acid, thus resulting in lower selectivity. Hence,many efforts have been made to develop some efficient and selective catalytic systems for controlled oxidation of toluene with molecular oxygen, including copper (II) complexes, Mnsalen complex, and manganese or cobalt tetraphenylporphyrin.
N-Hydroxyphthalimide (NHPI) is widely recognized as a carbon-radical-producing catalyst for various free-radical-mediated reactions . Ishii and his group developed an oxidizing system NHPI/O2/Co(II), which is able to efficiently catalyze the oxidation of a large variety of organic compounds under mild conditions at moderate oxygen pressure and temperature. The oxidation of toluene was carried out in the presence of NHPI (10 mol%) and Co(OAc)2 (0.5 mol%) in acetic acid solution for 20 h under ambient conditions produced benzoic acid in 81 % yield . Jiang et al. also prepared Benzoic acid from aerobic oxidation of toluene using manganese dioxide (MnO2) and NHPI as catalysts. In order to improve the selectivity of benzaldehyde and benzyl alcohol among the products, our team has investigated liquid-phase solventfree oxidation of toluene using an SBA-15-immobilized N,N-bis(salicylidene) ethylenediiminocobalt (Cosalen) complex and NHPI as catalyst . Among the NHPIcatalyzed oxidation systems combined with metal salt and complex, the immobilization and recycle of metals was already investigated. A silica gel supported cobalt(II) Schiff base complex was used as an effective and reusable catalyst into selective oxidation of alkyl aromatics in combination with NHPI under oxygen at atmospheric pressure. However, a major problem is that NHPI as a main catalyst can decompose to phthalimide and phthalic anhydride, or form inactive trimers, thus requiring a larger amount of NHPI for the reaction. Recovery and recycle of NHPI remains a significant limitation that restricts the application of NHPI. To our knowledge, little work has been done regarding the reuse of NHPI. The use of a novel supported NHPI promoter by a coupling reaction was reported, but in acetic acid as a solvent. In the aerobic oxidation of cumene, Melone et al. recovered the catalyst NHPI at the end of the oxidation process by removal of polar co-solvent, with consequent precipitation of NHPI. The resulting filtered mixture is treated with nonbasic supports, the adsorbing solids can be regenerated by washing with a polar solvent, allowing the recovery of residual catalyst. Immobilization of NHPI on silica has been achieved by impregnation in the oxidation of cycloalkanes with favorable results, but the loss of the active site NHPI was unavoidable.
SBA-15 mesoporous silica is a useful heterogenous carrier with high thermal stability, contains regular arrays of uniformly-sized channels . The amorphism of the pore walls gives rise to a substantial number of silanol groups, thus facilitating the grafting of catalytically active groups. N,N-dihydroxypyromellitimide (NDHPI), an analogue of NHPI, involves two hydroxyimide moieties. As reported, the catalytic activity of a hyroxyimide moiety of NDHPI is comparable to that of NHPI . In this work, SBA-15-immobilized NHPI through normal impregnation method and SBA-15-immobilized NDHPI through covalent bonding with Si–OH groups of SBA-15 by a new method were prepared and comparatively used as catalysts into toluene oxidation.

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jiangguofeng

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wj621798: 金币+5, 翻译EPI+1, ★★★★★最佳答案, 谢谢！ 2016-07-16 11:03:14

在化学工业上，通过分子氧对甲苯至苯甲醛、苯甲醇和苯甲酸的选择性催化氧化是一种重要的转化作用。然而,提高甲苯的转化率和对高附加值中间体的选择性仍然是一个挑战。 SINA工艺是用于制备己内酰胺的一种非常重要的工业生产方法。其中甲苯的液相氧化是于165℃和1.0 MPa由钴盐催化的，甲苯转化率14-15 %以及苯甲酸选择性92-93 %，但仅得到少量的苯甲醛和苯甲醇副产品。苯甲醛和苯甲醇是药物、食品、染料、香料和树脂一类多种化学品制造中的重要中间体。目前，苯甲醛和苯甲醇主要是通过苄叉二氯的水解生产的[5, 6]。然而上述方法不可避免地产生微量的氯，因此,在药物和食品工业中它的使用是被禁止的。因此、找到通过用分子氧控制的甲苯氧化生产苯甲醛和苯甲醇的新型环保的方法已受到更多关注。此外,苯甲醛和苯甲醇对次生氧化至苯甲酸更敏感,因而导致选择性更低。因此,已作出许多努力去开发一些有效的选择性催化系统用于由分子氧进行的甲苯受控氧化，其中包括铜络合物(II)、水杨醛缩乙二胺合锰络合物和四苯基锰卟啉或四苯基钴卟啉。
N -羟基邻苯二甲酰亚胺(NHPI)催化剂被普遍认为是一种用于各种自由基介导反应的碳自由基产生催化剂。石井及其团队开发了一种氧化系统，NHPI/O2/Co(II),这个系统能够在中等氧气压力和温度等温和条件下有效地催化多种有机化合物的氧化。环境条件下在NHPI(10 mol%)和Co(OAc)2 (0.5 mol%)存在下于乙酸溶液中进行20小时的甲苯氧化产生81 %收率的苯甲酸Jiang等人还使用二氧化锰(MnO2)和NHPI作为催化剂由甲苯的需氧氧化制备了苯甲酸。ysts. 为了提高这类产物的苯甲醛和苯甲醇的选择性,我们的团队已研究了使用SBA-15-固定的N,N -双（邻羟亚苄基）乙二亚胺合钴（共价）络合物和NHPI作为催化剂所进行的甲苯的液相无溶剂氧化作用。在与金属盐和络合物相结合的NHPI催化氧化系统当中金属的固定化和重复利用已经得到研究。一种硅胶负载的钴(II)席夫碱络合物被作为有效的并且可重复使用的催化剂和NHPI共同用于氧常压下烷基芳烃的选择氧化。然而,一个主要的问题是NHPI作为主催化剂能分解成苯邻二甲酰亚胺和邻苯二甲酸酐,或者形成惰性的三聚物,因而这种反应需要大量NHPI。NHPI的回收和重复利用仍然是制约NHPI应用的明显的限制。据我们所知,几乎没有就NHPI的重复使用进行过研究。有报导一种新颖的负载型NHPI助催化剂用于一种偶联反应,但是是于作为溶剂的乙酸中进行的。马龙等人在枯烯的有氧氧化中通过在氧化过程结束时除去极性共溶剂及随后的NHPI沉淀回收NHPI催化剂。得到的过滤后的混合物用非碱性载体处理,这种吸附性固体物可以通过用极性溶剂洗涤进行再生,回收残留的催化剂。通过在环烷烃的氧化过程中浸渗已完成了NHPI于硅石上的固定化并取得良好的效果,但是活性部位NHPI的损失是不可避免的。
SBA - 15中孔二氧化硅是一种具有高热稳定性的有用的异相载体,带有规则排列的大小相同的沟槽。孔壁的无定形性产生大量的硅醇基团,因而有利于催化活性基团的接枝。N,N -二羟基均苯四酰亚胺, NHPI的一种同系物,包含两个羟基亚酰胺部分。据报导，NDHPI的羟基亚酰胺部分的催化活性可与NHPI相媲美。在本研究中, 通过普通浸渍法制备了SBA-15-固定的NHPI并按照新方法通过与SBA-15的Si-OH基团共价键合制备了SBA-15-固定的NDHPI，并且作为催化剂用于甲苯氧化中进行对比。

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