【作者】 户安军；

【导师】 吕春绪；

【作者基本信息】 南京理工大学 ， 应用化学， 2008， 博士

【摘要】 芳香醛是重要的有机合成中间体,在医药,农药,染料等方面具有重要的应用价值,传统生产芳香醛的方法是甲苯类化合物的氯化水解法,该方法带来了严重的环境污染。以氧气为廉价、清洁氧源实现甲苯类化合物的选择性氧化是一个极富挑战性和具有重大战略意义的课题,近年来引起了广泛关注。本文采用液相氧化法,主要探索了以下几个方面:（1）研究了醋酸-水混合溶剂中,Co（OAc）₂/Mn（OAc）₂/KBr催化剂催化下对氯甲苯的选择性氧化。采用醋酸-水混合溶剂代替通常所用的纯醋酸作为反应介质,避免了醋酸和水的分离,利于溶剂的回收利用。混合溶剂中金属组分会生成沉淀,大大降低了催化的活性,XRD、FT-IR、AAS分析显示沉淀为二氧化锰。发展并完善了沉淀的形成机理,通过系列实验证明了氧气直接氧化Mn（Ⅱ）或Mn（Ⅲ）对沉淀的形成几乎没有贡献,同时对影响沉淀形成的主要因素进行了探讨。对反应条件进行了优化,优化的反应条件如下:醋酸-水混合溶剂的初始含水量为10wt.%,Co/（Co+Mn）摩尔比和Br/（Co+Mn）摩尔比均为0.4,催化剂用量为对氯甲苯质量的4%、对氯甲苯/溶剂体积比为1.5、反应温度106℃、反应时间10h、氧气流速10mL/min。在优化的反应条件下,反应的转化率和选择性可达19.7%、72.4%,对氯苯甲醛收率可达14.3%。（2）针对Co（OAc）₂/Mn（OAc）₂/KBr催化体系中出现沉淀的问题,以对氯甲苯的选择性氧化为探针,对MC三组分催化剂进行了系统的探索。通过对第二金属组分、不同的金属盐或配合物、不同溶剂、不同引发剂的筛选,确定了较佳的三组分MC催化体系。研究发现,当以MnSO₄代替Mn（OAc）₂时,反应中几乎不生成沉淀,大大提高了催化剂的活性;并且在转化率相似时,Co（OAc）₂/MnSO₄/KBr催化剂的选择性与Co（OAc）₂/Mn（OAc）₂/KBr催化剂的选择性相差不大。对Co（OAc）₂/MnSO₄/KBr催化体系的反应条件进行了优化,较佳的Co/（Co+Mn）摩尔比为0.2、较佳的Br/（Co+Mn）摩尔比为0.3、较佳的反应的温度为106℃。混合溶剂的初始含水量是一个极为重要的因素,由于水对反应复杂的双重影响,催化剂的活性随初始含水量的变化呈现出复杂的变化趋势。反应过程中溴组分会转变为无活性的苄溴,在纯醋酸溶剂中,催化剂会因苄溴的形成而发生催化剂失活现象;在醋酸-水混合溶剂中,由于水对苄溴的溶剂化作用会使苄溴还原为溴离子,一定程度上保持了催化剂活性;并且在一定范围内,含水量的提高有益于生成醛选择性的提高,研究表明,将混合溶剂的初始含水量控制在5-10wt.%是较为有利的。优化的反应条件下反应10h,对氯甲苯的转化率可达33.7%,生成醛的选择性为66.6%,对氯苯甲醛收率为22.4%,结果重现性良好。回收利用实验表明,在回收的催化剂中补加全部的溴组分和5%的金属组分,催化剂可以进行多次回收利用。该催化体系有较广泛的适用性,对甲苯、邻氯甲苯、2,4-二氯甲苯也具有较好的催化氧化性能。（3）将M（acac）_n/CH₃CHO仿生催化体系用于对氯甲苯的选择性氧化,研究了不同中心金属离子、催化剂用量、乙醛用量、氧气压力、反应时间及反应介质对反应的影响。在金属配合物中Co（acac）₃的催化性能最好,在其用量为0.764 mmol、乙醛用量为反应物物质的量的10%、氧气压力为2MPa时,以乙腈为反应介质,室温下反应11h,反应的转化率和选择性可达15.3%,87.2%,对氯苯甲醛收率可达13.3%;反应也可在无溶剂时进行,此时反应的转化率、选择性及醛的收率分别为:8.1%,89.1%,7.2%。更多还原

【Abstract】 Aromatic aldehydes are important intermediates in the production of pharmaceuticals, agricultural chemicals,and dyes,traditionally manufactured mainly by the chlorination of methylbenzenes to form benzylchlorides which are then subjected to acid hydrolysis, leading to serious pollution.Selective oxidation of methylbenzenes with oxygen as a cheap and clean oxidant still remains a chemical challenge and is a strategic subject,which,in recent years,attracts much attention.Using the strategy of liquid-phase oxidation,the following aspects have been explored in the present work.（1）Selective oxidation of p-chlorotoluene catalyzed by Co（OAc）₂/Mn（OAc）₂/KBr in acetic acid-water mixed solvent was studied.Acetic acid-water was used as the reaction medium in place of the commonly used pure acetic acid,which avoids the nuisance of the acetic acid separation and is beneficial to the recover and reuse of the solvent.In acetic acid-water medium,the occurrence of precipitate leads to the great reduction of the catalytic activity.The precipitate has been analyzed by XRD,FT-IR and AAS,the results showing that the precipitate is manganese dioxide（MnO₂）.The mechanism of the precipitate formation has been supplemented and consummated.The fact that direct oxidation of Mn（Ⅱ）and Mn（Ⅲ）by oxygen barely contributes to the formation of the precipate has been verified by a series of experiments.The factors which influence the precipitate formation have been investigated.The reaction conditions have been optimized.The optimum reaction conditions were as follows: initial water concentration of the solvent 10 wt.%,Co/（Co+Mn）mole ratio 0.4, Br/（Co+Mn）mole ratio 0.4,amount of the catalyst accounting for 4 wt.%of the substrate,p-chlorotoluene/solvent volume ratio 1.5,reaction temperature 106℃, reaction time 10h,and the oxygen flow rate 10 mL/min.Under these conditions, 14.3%yield of p-chlorobenzaldehyde was obtained at 19.7%conversion of p-chlorotoluene with 72.4%selectivity.（2）To solve the problem of precipitation in the Mn（OAc）₂/Co（OAc）₂/KBr catalytic system, the three-component MC catalytic system has been systematically studied using the selective oxidation of p-chlorotoluene as a probe.By the selection of the second metal component,different metal salts and complexes,different solvents,and different initiators,a superior three-component MC catalytic system has been defined.It was found that when MnSO₄ is used in place of Mn（OAc）₂,precipitate barely forms,and the catalytic activity greatly enhances.Moreover,at similar conversions,there is no significant difference in selectivity between the Co（OAc）₂/MnSO₄/KBr catalytic system and the Co（OAc）₂/Mn（OAc）₂/KBr catalytic system.The reaction conditions of the Co（OAc）₂/MnSO₄/KBr catalytic system have been optimized,and the optimum Co/（Co+Mn）mole ratio,Co/（Co+Mn）mole ratio and reaction temperatures are 0.2,0.3, and 106℃respectively.The initial water concentration of the mixed solvent is an extremely important factor.Due to the complex double effects of water on the reaction, with the change of the initial water concentration,the catalytic activity shows complex changing trend.During the reaction,the bromide component has been converted to catalytically inactive benzylic bromide.In pure acetic acid medium,the "catalyst failure" occurs owing to the formation of benzylic bromide while in acetic acid-water medium,the solvolysis of benzylic bromide by water maintains the catalytic activity to some extent.And in certain range,the increase of the initial water concentration enhances the selectivity.It was demonstrated that it is beneficial to control the initial water concentration in the range of 5-10wt.%.Under the optimum reaction conditions, after 10h of reaction,22.4%yield of p-chlorobenzaldehyde was obtained at 33.7% conversion of p-chlorotoluene with 66.6%selectivity and the results are reproducible. The recycle experiments show that the recovered catalyst could be reused for many times provided the total bromide component and 5%metal component（Co and Mn） were replenished.This catalytic system is applicable in a wide range of substrates, showing good catalytic properties in the oxidation of toluene,o-chlorotoluene,and 2, 4-dichlorotoluene.（3）A biomimetic catalytic system M（acac）_n/CH₃CHO has been used in the selective oxidation of p-chlorotoluene.The effects of the center metal ions,the amount of catalyst and ethanal,the oxygen pressure,the reaction time,and the reaction solvents on the selective oxidation were investigated.The results show that among the acetoacetonate complexes,Co（acac）₃ has the best catalytic activity.The optimum reaction conditions were as follows:0.764 mmol of Co（acac）₃,mole fraction of ethanal 10%based on the substrate,room temperature,oxygen pressure 2 MPa,reaction time 11h and solvent acetonitrile.Under these conditions,13.3%p-chlorobenzaldehyde was obtained with 15.3%conversion and 87.2%selectivity.The oxidation can also be carried out without solvent with 8.1%conversion,89.1%selectivity and 7.2%yield respectively.更多还原