节点文献
模拟酶催化分子氧对乙苯及其衍生物侧链氧化的研究
The Oxidation of the Side Chain on Ethylbenzene and Its Derivatives Catalyzed by Biomimetic Catalyst
【作者】 李小港；
【导师】 何仁；
【作者基本信息】 大连理工大学 ， 应用化学， 2008， 博士
【摘要】 饱和C-H键的氧化是合成有机含氧化合物的重要方法。随着石油化学工业的发展，许多烃类饱和C-H键的氧化技术已成功地应用到工业生产中，例如环己烷氧化制环已醇／环已酮（俗称KA油）、对二甲苯氧化制对苯二甲酸、甲苯氧化制苯甲酸等。此外，乙苯及其衍生物的侧链亚甲基氧化制备芳酮的反应也具有很广阔的应用前景。芳酮是合成染料、香料及医药等精细化学品的原料，工业上主要通过Friedel-Crafts酰基化来制备。但是，在Friedel-Crafts反应中，催化剂AlCl3在水解过程中产生大量的酸性废水，对环境造成危害。随着催化氧化技术的发展，高转化率、高选择性的氧化饱和C-H键成为可能。乙苯及其衍生物的侧链氧化制备芳酮的方法越来越受到重视。其中最有代表性的是乙苯氧化制苯乙酮。此外，像对硝基苯乙酮、二乙酰基苯等因原料苯环上含有强吸电子基团，很难通过Friedel-Crafts酰基化得到，而通过乙苯及其衍生物侧链氧化就很容易了。细胞色素P-450是生物体内的一种氧化酶，在常温下能高效、高选择性的催化分子氧氧化饱和C-H键，对于开发绿色环保氧化工艺具有重要意义。对P-450活性中心的结构和功能模拟引起了人们的极大兴趣。细胞色素P-450的活性中心为卟啉铁，因此近年来许多金属卟啉配合物被用来催化氧化反应。基于此，本文模拟细胞色素P-450合成了12个过渡金属卟啉配合物，并用它们催化活化分子氧对乙苯及其衍生物侧链氧化。发现四-（五氟苯基）卟啉（TPFPP）过渡金属配合物中心金属的还原电位越高，催化活性也越好，如四-（五氟苯基）卟啉钴（14）的氧化还原电位最高，它的催化活性也最好；在14浓度为1．0×10-3mol／L，氧气压力为1．5 MPa，100℃，反应24 h的最佳反应条件下，乙苯转化率为38．6％，苯乙酮的选择性为94．0％，1-苯基乙醇的选择性为6．0％，是目前文献报道的最好结果；烷基芳烃的苯环上含供电子基团或侧链增长，转化率下降，苯环上有吸电子基团，转化率升高。对14催化分子氧氧化乙苯侧链进行紫外-可见光谱研究发现只有出现435 nm吸收峰时反应才能发生；核磁共振谱确认该435 nm的物种是[TPFPPCo（Ⅲ）]OH。由此推出，14与P-450类似，在反应中它先与分子氧生成TPFPPCoOO·超氧配合物，随后按P-450酶催化机理和自由基两种机理进行反应。在反应中[TPFPPCo（Ⅲ）]OH分子间缩水而生成TPFPPCo（Ⅲ）O（Ⅲ）CoTPFPP从反应体系中沉淀出来，它的催化活性很低。形成μ-O-双核配合物是催化剂失活的主要原因。研究K2Cr2O7对14催化分子氧对乙苯侧链氧化的促进作用。当K2Cr2O7：乙苯（mol）=1：800，14浓度为1．0×10-3 mol／L，氧气压力为1．5 MPa，100℃反应24 h，乙苯转化率就达到55．2％，远高于14催化的结果。苯乙酮选择性达92．4％，1-苯基乙醇的选择性7．6％。K2Cr2O7并非促进形成活性物种而是加速过氧化物分解。本文合成2，6-二[1-（苯基亚胺基）乙基]钴合二氯（22）、2，6-二[1-（苯基亚胺基）乙基]锰合二氯（23）和二{2，6-二[1-（苯基亚胺基）乙基]}钴合四氯化钴（24）等三个配合物并对它们做了单晶结构分析。结果表明22和23中三个氮均与金属配位，并处在同一平面上，形成扭曲的三角双锥型。24是由22在CH2Cl2中岐化得到的六氮配位钴配合物，具有扭曲的八面体构型。研究了这类配合物催化分子氧对乙苯及其衍生物侧链氧化的反应。发现它们的性能与四-（五氟苯基）卟啉过渡金属差不多，也是一类模拟酶氧化催化剂，钴配合物22的催化活性也是最高。在22浓度为1．5×10-3mol／L，氧气压力为1．0 MPa，120℃反应20 h，乙苯转化率为37．8％，苯乙酮的选择性为82．5％，1-苯基乙醇的选择性为13．5％，锰配合物23次之。从钻配合物24的单晶结构可知，中心金属钴与六个氮原子配位，配位数达到饱和，结构比较稳定，所以其催化活性最低。
【Abstract】 The oxidation of saturated C-H bond is an important technical method to obtain oxygenous organic compounds. With the development of petroleum chemical industry, many oxidation technologies have been applied triumphantly. For example, cyclohexane can be oxidized into a mixture of cyclohexanol and cyclohexanone, p-xylene to terephthalic acid and the toluene to benzoic acid and so on. In addition, the oxidation of the side chain on alkybenzene is a promising route to get ketone product.Arocmatic ketones as an important material are mainly gained from the Friedel-Crafts acylation of arene in chimecal industry. During the Friedel-Crafts acylation of arene, much acidic waste water was produced from the hydrolys of AlCl3, which caused the harm to the environment. With the development of the oxidation technologies, saturated C-H bond can be oxidized with high conversion and excellent selectivity. More and more attention has been paid to the oxidation of the side chain on the ethylbenzene and its derivatives. A typical example is the oxidation of ethylbenzene to prepare acetophenone. Furthermore, p-nitroacetophenone and p-diacetylbenzene which can not be obtained through the Friedel-Crafts acylation reaction owing to electron-withdrawing substituent on the phenyl ring. On the contrary, they can be easily prepared by the oxidation of the corresponding alkylbenzene.Cytochromes P-450 as an enzyme can catalyze the oxidation of saturated C-H bond with high conversion and excellent selectivity under mild condition. The active site of cytochromes P-450 is iron porphyrin. In recent years, many metalloporphyrins were synthesized to catalyze the oxidation reaction. Encouraged by these achievements, in this thesis, 12 transitional metalloporphyrins were synthesized in order to mimic the oxidation function of cytochromes P-450. The activation of molecular oxygen and oxidation of the side chain of ethylbenzene or its derivatives catalyzed by these complexes without additive was investigated. The results showed that the higher reduction potential the metalporphyrin has the better catalytic activity. In our case. （5, 10, 15, 20）-tetrakis（pentaflurophenyl）porphyrin cobalt（II） （14） with the highest reduction potential exhibited the highest catalytic activity. Under the optimal conditions (1×10-3 mol/L of 14, 1.5 MPa of O2, 100℃, 24 h), the conversion of ethylbenzene was 38.6%, the selectivity of acetophenone and 1-phenylethynol was 94.0% and 6.0% respectively. It was the best result in the literature. The electron-donating groups on the phenyl ring and the longer side chain on the alkylbenzene decreased the conversion, on the contrary, the electron-withdrawing substituent on the phenyl ring enhanced the conversion.The side chain oxidation reaction of ethylbenzene with molecular oxygen catalyzed by 14 was investigated by UV-Vis spectra. The intermediate specie with signal at 435 nm was further confirmed by 1H NMR to be [TPFPPCo（Ⅲ）]OH. Therefore, it can be deduced that the mechanism of the ethylbenzene oxidation with molecular oxygen catalyzed by 14 is analogous with the oxidation of alkane catalyzed by cytochromes P-450. Firstly, TPFPPCo（Ⅱ） and molecular oxygen generate TPFPPCoOO·species, then the oxidation reaction of ethylbenzene works according to two kinds of mechanisms, i.e. the metal-based mechnism and the radical chain mechanism. During the reaction, TPFPPCo（Ⅲ）O（Ⅲ）CoTPFPP precipitated from the reaction mixture by condensation of two molecular [TPFPPCo（Ⅲ）]OH. The low catalytic activity was assumed to be the catalyst deactivation by the formation ofμ-O dimer complex.The stimulation of K2Cr2O7 for the side chain oxidation of ethylbenzene with molecular oxygen catalyzed by 14 has been investigated. Under the optimal conditions (K2Cr2O7:ethylbenzene = 1:800, 1×10-3 mol/L of 14, 1.5 MPa of O2, 100℃, 24 h), the conversion of ethylbenzene was 55.2%, and the selectivity for acetophenone was 92.4%, better than 14 alone. Experimental results show that the function of K2Cr2O7 is not the promotion of the formation of catalytic species, but accelerating the decomposition of the peroxide.In order to compare their catalytic performance with metalloporphyrins, we synthesized 2,6-bis[（1-phenylimino）ethyl]pyridine dichloride cobalt（Ⅱ） （22）,2,6-bis[（1-phenylimino）ethyl]pyridine dichloride manganese（Ⅱ） （23） and bis{2,6-di[（1-phenylimino）ethyl]pyridine}cobalt（Ⅱ） tetrachlorocobaltate （24）. The single crystal X-ray structures of these complexes showed that the core metal atom is ligated by three N atoms from ligand in complex 22 and 23, located in a distorted trigonal bypyramidal geometry with the three N atoms and the core metal atom being coplanar. The complex 24 was formed by disproportion from 22 in CH2Cl2. The X-raystructure of complex 24 showed a octahedral geometry in which the Co（Ⅱ） atom is coordinated by six N atoms from two ligands. The side chain oxidation of ethylbenzene with molecular oxygen catalyzed by these complexes in the absence of any additives was also investigated, where Co complex （22） showed the highest catalytic activity. Under the optimal conditions (1.5×10-3 mol/L of 22, 1.0 MPa of O2, 120℃, 20 h), the conversion of ethylbenzene was 37.8%, and the selectivity for acetophenone and 1-phenylethynol was 82.5% and 13.5% respectively. The catalytic activity of Mn complex （23） was inferior to its Cobalt counterpart 22. The complex 24 had exihibited the lowest catalytic activity because the Co atom was coordinated six N atoms.