【作者】 李彦威；

【导师】 王志忠；

【作者基本信息】 太原理工大学 ， 应用化学， 2007， 博士

【摘要】 苯甲醛及其衍生物是一类重要的有机化合物，应用领域非常广泛，它可用于合成药物、香料、化妆品、染料和农药等多种化工产品，具有年需求量大、市场前景好和经济效益高的特点。对制备苯甲醛及其衍生物的方法进行研究和理论性探讨，不仅具有良好的经济效益，而且具有较高的学术价值，多年来一直是化学工作者研究的重点课题内容。本论文采用在线超声电合成的方法制备苯甲醛及其衍生物，并对其过程和机理进行研究。在研究中选择甲苯和二甲苯为原料，分别以Mn（Ⅲ）／Mn（Ⅱ）、Ce（Ⅳ）／Ce（Ⅲ）和MnO₂／Mn（Ⅱ）为氧化媒质，通过超声电氧化的方法，电解得到相应的氧化剂Mn（Ⅲ）、Ce（Ⅳ）和MnO₂，并在超声波作用下，将其用于氧化原料制备相应的苯甲醛及其衍生物。超声电合成方法是将超声波技术和电解合成技术有机地结合在一起，充分利用超声波良好的搅拌、乳化和对电极表面所产生的清洗、除气、去钝化等作用，以及电解合成技术所具有的高效、节能、选择性高、反应条件温和、设备通用性强等特点，促进油／水相间的充分接触，加快传质过程，缩短反应时间，提高反应收率。它克服了传统的有机合成工艺的弊端，强化了原有的电解合成技术。由于参与反应的除反应物外，只有电子“试剂”，因而，它不仅是精细化工领域中的一种高效节能新工艺，而且是一种对环境基本无污染的清洁合成技术，也是目前超声电化学研究的前沿领域之一。本研究为检验产品质量，调整合成工艺条件，根据电合成过程中生成物的组成情况，首先建立了无需进行分离就能够简单、快速、准确测定目标产物的紫外分光光度法和反相高效液相色谱法，并将其应用于产品含量的测定，获得令人满意的实验结果。通过对两种分析方法进行比较，发现反相高效液相色谱法不仅线性范围宽，回收率高，而且还能用于甲基苯甲醛和马来酸含量的测定。因此，本实验的目标产物均采用反相高效液相色谱法进行分析。施加超声波于电氧化Mn（Ⅱ）为Mn（Ⅲ）的过程中，由于它能够持续地冲击、清洗电极表面，驱除电极附近的气泡，保持电极表面活性，不仅加快了传质速率，降低了氧化电位，提高了电流效率，而且使电解反应所需时间和硫酸浓度均低于机械搅拌法，显示了超声波独特的作用效果。本实验通过电解条件的优化，得到了电氧化Mn（Ⅱ）为Mn（Ⅲ）的最适宜反应条件为：电解时间4100s，电流密度0.09A／cm²，硫酸浓度5.5mol／L，硫酸锰浓度0.4mol／L，电解温度20℃，超声波频率为59kHz，超声波输出功率175W。在此条件下，其电解电流效率达到了84.79％。将超声波应用于以Mn（Ⅲ）为氧化剂制备苯甲醛和三种甲基苯甲醛的有机相／水相体系的氧化反应中，所用氧化液不仅可电解再生，重复利用，而且其效果基本不变，电流效率下降小于4％，而苯甲醛的收率降低小于2％。本研究得到的氧化甲苯制备苯甲醛的条件为：反应温度60℃，甲苯与Mn（Ⅲ）的摩尔质量之比为4：1，硫酸浓度为7.0mol／L；超声波频率59kHz，超声波功率175W。而将此方法应用于氧化二甲苯制备对、邻、间甲基苯甲醛时，超声波的作用更加明显，由于它能够减小分子中二甲基间的空间阻碍效应，不仅降低了硫酸的使用浓度，无需调节酸度就可满足反应的要求，而且与搅拌相比，显著提高了产物的收率，对甲基苯甲醛、间甲基苯甲醛、邻甲基苯甲醛的收率分别提高了4.3％、19.0％和20.7％。在实验中发现，无论是在电解反应还是在氧化反应过程中，对超声波频率的选择均倾向于高频率，这可能是由于超声波频率为59kHz时与空化泡的自然频率比较接近，使二者能够达到最有效的能量耦合，充分发挥了超声波的作用。而有关超声波功率的影响，在电解反应过程中其呈起伏波动性，而在氧化过程中则具有较好的规律性。这可能是由于超声波空化作用形成的微射流、冲击流等作用受超声波功率的影响比较大，而由超声波引起的乳化反应等次级效应，受功率的影响不是太突出的缘故。同时实验结果表明，施加超声波并没有改变电解反应中Mn（Ⅱ）的氧化机理，它不是直接与Pb电极进行电子交换，而是与Pb电极表面生成的Pb（Ⅳ）来交换电子，被Pb（Ⅳ）氧化生成Mn（Ⅲ），Pb（Ⅳ）被还原后在电极表面再生。并且在超声波辐射下，不仅降低了电解电位，而且有效地提高了电解收率和电流效率。在研究中还对超声电合成制备Ce（Ⅳ）氧化液和Ce（Ⅳ）氧化甲苯及其衍生物生成相应苯甲醛类化合物的过程和机理进行了探讨。由于在无隔膜电解槽中，阴极能够还原阳极生成的Ce（Ⅳ），降低其电解收率。因此，采用隔膜电解槽，选择PbO₂／Pb电极作阳极、纯Pb电极作阴极的双电极电解体系，通过正交试验和单因素实验找出了不同因素对电流效率或电解收率的影响规律，综合考虑电流效率、电解收率、电能效率、时空效率等方面的因素，确定了恒电流电解氧化Ce（Ⅲ）的适宜条件为：超声波频率59kHz，超声波功率250W，电流密度0.06A／cm²，通过电量1.0F／mol，阳极液的组成为0.40mol／L Ce（Ⅲ）+0.50mol／L H₂SO₄，阴极液的组成为0.50mol／L H₂SO₄。该条件下电解氧化Ce（Ⅲ）为Ce（Ⅳ）的电流效率和电解收率均可达到87.93％。同时，在超声波频率59kHz，超声波功率250W；反应温度75℃，甲苯（或二甲苯）与Ce（Ⅳ）的摩尔质量比为3：1，硫酸浓度7.5mol／L（4.0mol／L）的条件下，Ce（Ⅳ）氧化甲苯（或二甲苯）制备苯甲醛和对、间、邻甲基苯甲醛的收率分别达到了95.78％、84.7％、81.8％和73.5％。实验中采用循环伏安法对其电极反应机理进行研究发现，Ce（Ⅲ）主要是通过在电极表面直接失去电子而被氧化生成Ce（Ⅳ），并通过极化曲线法得到了验证。将作为氧化媒质的Ce（Ⅳ）／Ce（Ⅲ）与Mn（Ⅲ）／Mn（Ⅱ）进行对比分析可以看出：①以Ce（Ⅳ）为氧化剂氧化甲苯或二甲苯制备苯甲醛和甲基苯甲醛的效果好于Mn（Ⅲ），其产物收率均高出后者10％～15％。②二者的电解氧化反应机理有所不同，Ce（Ⅳ）由Ce（Ⅲ）直接电氧化得到，而Mn（Ⅲ）则是由Mn（Ⅱ）间接电氧化获得，且前者电解氧化所需的硫酸浓度仅为后者的十分之一。③二者所采用的电解槽形式不同，前者为隔膜式，而后者为无隔膜式，前者相对比较复杂。④在电解氧化Ce（Ⅲ）为Ce（Ⅳ）时，通过电量1.0 F／mol所需时间约为5.36h，是电解氧化Mn（Ⅱ）为Mn（Ⅲ）的4.7倍。因此，综合考虑上述情况，若能充分利用阴极反应，选择Ce（Ⅳ）／Ce（Ⅲ）为氧化媒质，间接电氧化甲苯或二甲苯制备苯甲醛和甲基苯甲醛将更加有利。本实验针对电解氧化Ce（Ⅲ）为Ce（Ⅳ）所面临的无隔膜电解收率低，而隔膜电解能耗高的问题，建立了一个新的成对电解体系，即在线超声离子膜耦合成对制备Ce（Ⅳ）和丁二酸。实验结果表明：新的成对电解体系不仅完全可行，而且阴、阳极的电流效率与电解收率（或转化率）都比较高；阴极电解的平均电流效率为92.71％，阳极电解的平均电流效率为87.81％，总的电流效率高达180.52％。马来酸电还原为丁二酸的转化率达到了92.09％，电解的槽电压与单纯电解氧化Ce（Ⅲ）相比降低了0.25V。采用熔点测定、红外光谱解析和纯度测定，对阴极电解产品进行了分析，证明该产品为丁二酸，其含量大于99.0％。实验中采用在线超声电氧化的方法，对两种不同材料的电极电解MnSO₄酸性溶液制备微粒MnO₂的条件进行了优化和对比分析，探讨了各种因素的影响机理，并通过激光粒度分析仪、红外光谱仪和X射线衍射仪对微粒MnO₂进行了表征，测定了微粒的粒径大小、比表面积和晶相构成等。实验发现采用Pt网电极电解得到的MnO₂颗粒粒度远远小于用PbO₂—Pb电极制得的，前者比表面积约是后者的54倍，颗粒粒径前者＜1μm的占到80％以上，后者却未测到；表征结果显示，尽管Pt网电极电解产物是一α-MnO₂和γ-MnO₂的混合晶体，但却以γ-MnO₂晶相为主。因此，将其用于氧化甲苯制备苯甲醛的实验中，并与购买的分析纯试剂MnO₂进行对比，电解制得的MnO₂具有更高的氧化活性，氧化得到的苯甲醛产品收率更高。实验中发现，无论采用Mn（Ⅲ）、Ce（Ⅳ）和MnO₂中的那一种氧化剂氧化二甲苯制备甲基苯甲醛，均得到完全相同的实验现象，即制备三种甲基苯甲醛所需的氧化反应时间顺序依次为对甲基苯甲醛＜间甲基苯甲醛＜邻甲基苯甲醛；而氧化产物的收率顺序则为对甲基苯甲醛＞间甲基苯甲醛＞邻甲基苯甲醛。表明二甲苯的氧化对位最容易，间位次之，而邻位的最困难。并且施加超声波可明显提高目标产物的收率。更多还原

【Abstract】 As an important species of organic compound, benzaldehyde and its derivatives were widely used in synthesis of many kinds of chemicals, such as Pharmaceuticals, spiceries, cosmetics, dyes, pesticide, etc. It has high annual demands, promising market and good economic benefits. Studying theoretically and practically on the methods for its preparation has been all along a significant project for the chemist, since it has both good economic benefits and high academic values.In this paper, benzaldehyde and its derivatives were prepared by electrosynthetic method with on-line ultrasound; meanwhile the course and the mechanisms were studied. In the research, toluene and xylene were employed as raw materials, Mn（III）/Mn（ II） , Ce（IV）/Ce（III） and Mn（ II ）/MnO₂ as oxidative medias, respectively. Corresponding oxidants Mn（III）, Ce（IV）, MnO₂ were electrolyzed through sonoelectrooxidation method, and were applied to oxidate the raw materials to prepare benzaldehyde and its derivatives under the ultrasonic radiation. Sonoelectrosynthesis is a method in which the electrolysis-synthesis technique and the ultrasonic technique were well combined, and it took full advantage of ultrasonic functions such as well-stirring, emulsification and effects of cleaning, purging, depassivating to the electrodes’ surface; meanwhile it made the best of electrolytic technique’s merits such as high efficiency, low energy consumption, high selectivity, warm reaction conditions and general equipments. Thus oily phase and water phase were contacted sufficiently, and mass transfer was promoted, which resulted in less reaction time and high product yields. This method overcame the weak points of traditional organic synthetic technique; moreover it strengthened the primary electrosynthetic technique. As only electron agent aside from the reactants took part in the reaction, it was not only a new effective and energysaving technics in the fine chemical engineering area, but also a clean synthetic way with nearly no pollutions to the environment, and that it was an advanced field of sonoelectrochemistry nowadays.In order to detect product’s quality and to adjust the synthetic conditions, UV and RP- HPLC methods for the determination of the target product were established according to the components of products in the electrosynthesis course, by which target product were able to be simply, fast and accurately determined without separation in advance. And satisfactory results were obtained when they were applied to the determined of the product’s content. By comparing the two analytical methods, it was found that RP-HPLC method had a wide linear range, and a high recovery, furthermore it was applicable to content determination of tolualdehyde and maleic acid. Therefore, all the target products on the experiment were analyzed by RP-HPLC method.When ultrasound was brought into the course of electrooxidating Mn（ II） to Mn（III） , it could continuously swash and clean the electrode surface, cleared away the air bubbles around the electrode and maintained its activity. As a result, mass transfer rate was increased, while oxidative potential was decreased, and current efficiency was promoted. What’s more, it made the electrolytic reaction time less and the concentration of sulfuric acid lower than those by mechanical stirring. All mentioned above indicated a special function of ultrasound. By optimizing the electrolytic conditions in the experiment, best reaction conditions for the electrooxidation of Mn（ II） to Mn（III） were given as : Electrolytic time was 4100s, current density was 0.09A/cm² , concentration of sulfuric acid was 5.5mol/L, concentration of manganese sulfate was 0.4mol/L, electrolytic temperature was 20℃, ultrasonic frequency was 59kHz, and ultrasonic output power was 175W. In this case, the current efficiency of electrolysis was up to 84.79%. When ultrasound was employed in the heterogeneous reaction of preparation for benzaldehyde and three species of tolualdedhyde, the oxidant solution could be reproduced and utilized repeatedly by electrolysis with little changes of the effect that less than 4% and 2% decrease in the current efficiency and benzaldehyde’s yield respectively. Conditions of benzaldehyde’s preparation by oxidizing toluene in the research were obtained as follows: reaction temperature was 60℃, mole ratio of toluene and Mn（II） was 4:1, concentration of sulfuric acid was 7.0mol/L, ultrasonic frequency was 59kHz, and ultrasonic output power was 175W. While the method was applied to prepare p-,m-,o-tolualdehyde by oxidizing corresponding xylene, the effect of ultrasound was more remarkable. As it could reduce the spatial block effect between the two methyl group in the molecule, concentration of sulfuric acid needed was decreased, thus it could met the demands in the reaction without adjusting the acid concentration. Moreover, product’s yield was apparently improved compared with stirring. The yield of p-tolualdehyde, m-tolualdehyde, and o-tolualdehyde was increased by 4.3%, 19.0% and 20.7%, respectively.In the experiment it was found that the higher ultrasonic frequency was always apt to be chosen whether in the electrolysis or in the oxidation. This might be because the ultrasonic frequency of 59kHz was more close to the natural frequency of the air bubble, which caused a most effective energy coupling of the two, thus the function of ultrasound could be fully carried out. The effect of ultrasonic power fluctuated in the electrolytic course, this might result from that the effect of ultrasonic power had a stronger effect to the microjet and the shockflow caused by cavitation of ultrasound than that to the subeffect such as emulsification. Meanwhile, experimental results showed that it didn’t change the oxidative mechanism of Mn（II） in the electrolysis when the ultrasound was introduced in. Mn（II） didn’t directly exchange electrons with Pb electrode, but exchanged electrons with Pb（IV） created on the Pb electrode surface, that was, Mn（II） was oxidized into Mn（III） by Pb（IV）, which was reproduced on the electrode surface after reduced. Under ultrasonic radiation, electrolytic potential was diminished; in contrast, electrolytic yield and current efficiency were promoted effectively.In the study, the procedures and mechanisms of preparing Ce（IV） oxidative solution and of producing compounds like benzaldehyde by oxidation of toluene and its derivatives with Ce（IV） were discussed. In undivided electrobath, cathode would reduce the Ce（IV） just created on the anode, which caused a decease of the electrolytic yields. Therefore, divided electrobath was employed, and a dielectrode system with PbO₂/Pb electrode as anode while pure Pb electrode as cathode was chosen. Affecting rules of different factors to the current efficiency or the electrolytic yield were found out through orthogonal experiments and solofactor experiments. With integrated consideration of current efficiency, electrolytic yield, electrical efficiency, spatio-temporal efficiency and so on, suitable conditions for galvanoplastics electrooxidation of Ce（III） were as follows: ultrasonic frequency was 59kHz, ultrasonic power was 200W, current density was 0.06A/cm², electricity passed through was 1.0F/mol, anodic electrolyte was composed of 0.4mol/L Ce（III） and 0.5mol/L H₂SO₄, cathodic electrolyte was merely 0.5mol/L H₂SO₄. On these conditions, both the current efficiency and electrolytic yield of electrooxidating Ce（III） to Ce（IV） could reach 87.93%. Moreover, on the occasion that ultrasonic frequency was 59kHz, ultrasonic power was 200W, reaction temperature was 75℃, mole ratio of toluene or xylene and Ce（IV） was 3:1, concentration of sulfuric acid was 7.5mol/L（4.0mol/L for xylene）, the product yield could be up to 95.78%, 84.7%,81.8% and 73.5% respectively, when Ce（IV） was utilized to oxidize toluene or certain xylene for preparation of benzaldehdye and p-,m-,o-tolualdehyde. Meanwhile, mechanisms of electrode reaction was studied by cyclic voltammetry, and it was found that Ce（III） was mainly oxidized into Ce（IV） by releasing electrons directly on the electrode surface, which was proved by polarization curves subsequently.Comparing Ce（IV） /Ce（III） with Mn（III）/Mn（ II） oxidative medias, we learned that:①A better results could be achieved using Ce（III） than using Mn（III） as oxidant to prepare benzaldehyde and tolualdehyde from toluene or xylene with the product’s yield 10%～15% higher;②Mechanisms of the two electrooxidation reaction were different from each other. Ce（IV） was directly oxidized from Ce（III）, but Mn（III） was produced by indirect electrooxidation of Mn（ II）, and concentration of sulfuric acid needed in the former was only one tenth of that in the latter;③Different electrobathes were employed. More complicated divided type was used in the former, while undivided type was used in the latter;④In the electrooxidation of Ce（III） to Ce（IV）, as 1.0F/mol electricity passed through 5.6 hours of time were needed, which was 4.7 times of that in Mn（ II） to Mn（III）. Therefore, with integrated consideration of the situations mentioned above, if the cathode reaction could be sufficiently utilized, preparation of benzaldehyde and tolualdehyde from toluene and xylene by electrooxidation with Ce（IV） /Ce（III） as oxidative media would be more advantageous.Concerning to the problems in electrooxidation of Ce（III） to Ce（IV） that undivided electrolysis had a lower yield while divided electrolysis consumed more energy, a new paired electrolytic system was set up, that was, ion membrane paired electrolysis for preparations of Ce（IV） coupling with succinic acid with on-line ultrasound. Experimental results showed that, the new paired electrolytic system was completely applicable; moreover, it was of high current efficiency and electrolytic yield （or transformation ratio） either on the anode or on the cathode. The average current efficiency was 92.71% and 87.81% on the cathode and the anode, respectively. Thus the total current efficiency was up to 180.52%. The percent of maleic acid transformed into succinic acid reached 92.09%, and the bath potential decreased by 0.25v compared with single electrooxidation of Ce（III）. Additionally, the electrolytic product arisen from the cathode was proved to be succinic acid with purity more than 99.0% by melting point test, IR spectrometry and purity test, etc.In the experiment, preparation conditions of particle MnO₂ by electrolyzing MnSO₄ acid solution with two kinds of electrode made of different materials were optimized and compared, effect mechanisms of different factors were discussed, and diameter, specific surface area and crystal phase of the particle MnO₂ was all determined by several means such as laser diameter analysis, IR and XRD.In the experiment it was found that the particle diameter of MnO₂ produced by grid Pt electrode was much smaller than that produced by PbO₂-Pb electrode. The specific surface area of the former was approximately 54 times as that of the latter. Particles with a diameter under 1 urn accounted to 80% above in the former, while it was not detected in the latter. From the test results, it was learned that, electrolytic product of grid Pt electrode was a mixture crystal ofα-MnO₂ andγ-MnO₂, however,γ-MnO₂ crystal was the major product. Therefore, it was used in oxidizing toluene to prepare benzaldehyde and compared with analytical reagent MnO₂. The results showed electrolytic MnO₂ was of higher oxidative activity, which resulted in a higher yield of benzaldehyde.Through the experiment it was found that no matter which one was employed for oxidizing xylene to prepare tolualdehyde, the same phenomenon turned up. That was, the sequence of oxidative reaction time needed in preparing the three kinds of tolualdehyde was p-tolualdehyde < m-tolualdehyde < o-tolualdehyde, while the sequence of the product’s yield was p-tolualdehyde > m-tolualdehyde > o-tolualdehyde. It indicted that paraxylene was most easily oxidized, and then was the metaxylene, while the orthaxylene was the last. What’s more, yield of the target product was apparently promoted when ultrasound was imposed on.更多还原