提高芬顿体系在醇类氧化反应中的活性和选择性外文翻译资料

 2022-05-01 09:05

Improvement the Activity and Selectivity of Fenton System in the Oxidation of Alcohols

Guoqiang Yang, Qiuxing Lin, Xingbang Hu, Youting Wu, and Zhibing Zhang

School of Chemistry and Chemical Engineering and National Engineering Research Center for Organic Pollution Control and Resource, Nanjing University, Nanjing 210093, China

Published 24 March 2014

Academic Editor: David W. Mazyck

Copyright copy; 2014 Guoqiang Yang et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

The reactivity and selectivity of Fenton system (Fe2 /H2O2) were improved with N-hydroxyphthalimide (NHPI) as cocatalyst. The oxidation process of benzyl alcohol to benzaldehyde has been studied. The reaction catalyzed by this new Fe2 /H2O2/NHPI system can be well performed under room temperature without adding any organic solvent. Besides, this catalyst system is effective for the oxidation of different alcohols.

1. Introduction

The Fenton reagent is a simple catalyst system which is composed of Fe2 and H2O2. In the reaction process with Fentonrsquo;s reagent, the hydroxyl radicals are generated rapidly at the presence of ferrous ion. This catalyst system is proved to be successful for the treatment of organic pollutants in industrial wastewater . There are numerous reports concerning pretreatment option to improve the biodegradability of complex wastes and recalcitrant from industry wastewater and landfill leachate. The original pollutants are often transformed to CO2 and H2O due to the strong oxidizing property of the Fenton system. In recent studies, Fenton system is coupled with other methods, such as membrane filtration and coagulation, to degrade organic compounds to a larger extent. Besides, the Fenton reagent is also effective in light alcohols and alkanersquo;s oxyfunctionalization, but the application for selective oxidation is rare.

The Fenton system has wonderful water solubility and there are abundant ferrous irons on the earth. Thus, it is possible to develop a mild and inexpensive water phase oxidation process using this system. Despite its numerous advantages, one limitation of traditional Fentonrsquo;s reagent must be taken into account: its high oxygen reactivity, which often leads to deep oxidation. To apply the Fenton system in chemical synthesis, the most crucial problem is how to control its reactivity and enhance its selectivity. The efficiency of Fentonrsquo;s reagent is affected by various factors, such as pH, the counterion of Fe2 , solvent, iron chelation, UV, and microwaves, which control the oxidation reactivity and regeneration ability of Fe2 from Fe3 . In addition, it has been found that the additives play a vital role to change the reactivity of Fenton system. For example, the reaction with KH2PO4 as additive provided high conversion and good selectivity in the oxidation of benzyl alcohol.

The objective of this study is to control the reactivity of Fenton system and enhance its selectivity. Based on a detailed investigation on a series of additives, we have found that the reactivity of Fenton system can be well controlled and the benzyl alcohol oxidation can be performed with good selectivity at room temperature in water.

2. Experimental

All the chemicals were obtained with purities higher than 99%. A typical experiment was carried out in a water bath. The alcohol (20thinsp;mmol), FeSO4·7H2O (0.5thinsp;mmol), and NHPI (0.5thinsp;mmol) were added to a glass reactor. 44thinsp;mmol H2O2 (30thinsp;wt% in water, 4.5thinsp;mL) was added with a syringe pump by 0.2thinsp;mL/min speed in 30thinsp;min. The reaction mixture was vigorously stirred (about 750thinsp;rpm). Reaction mixtures were analyzed using GC and GC-MS.

Different reaction conditions (temperature, concentration, Fe salt, and speed of adding H2O2) have been optimized.

3. Results and Discussion

3.1. The Influence of Different Additives

It has been revealed that some additives (such as KH2PO4 and KHSO4) to Fenton system can lead to a more effective oxidizing process at 70°C. The role of KH2PO4 was to control the pH of the solution which can change the rate to generate hydroxyl radicals. As a result, the selectivity of the reaction was enhanced. Encouraged by this idea, we have tried to further improve the reaction by adding different inorganic buffers in Fenton system. The influence of different additives (NaBF4, NaH2PO4, KH2PO4, and KHP) at 70°C was studied. Our results with KH2PO4 as additive were very close to those of a previous report. It seems that the adding of NaBF4, NaH2PO4, or KHP cannot give better results.

Performing reaction at room temperature is beneficial to save energy and develop safe process. The performance of these inorganic buffers was investigated at 25°C. Unfortunately, the reactivity of these catalyst systems is quite poor at room temperature. Though good selectivity can be obtained, the conversion is quite low. Increasing reaction time or changing the amount of additive could not improve the results at all. Though ionic liquids have shown attractive role in improving the reactivity of oxidation system, it se

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本实验以N-羟基邻苯二甲酰亚胺（NHPI）为助催化剂，提高了芬顿体系（Fe2 /H2O2）的反应性和选择性。本文研究了苯甲醇氧化制苯甲醛的过程。这种新的Fe2 /H2O2/NHPI体系的催化反应可以在室温下很好地进行，且不添加任何有机溶剂。此外，该催化剂体系对不同醇的氧化都是有效的。提高芬顿体系在醇类氧化反应中的活性和选择性

杨国强，林秋星，胡兴邦，吴悠婷，张志兵

南京大学化学化工学院，有机污染控制与资源国家工程研究中心，中国南京210093，2014年3月24日出版。

学术编辑：David W. Mazyck

版权所有（2014）为杨国强等。这是一篇在创作共享许可证下撰写的开放性学术论文，它允许在任何媒介中不受限制地使用和复制，只要适当引用原始作品。

摘要

一 .简介

芬顿试剂是一种简单的催化剂体系，由Fe2 和H2O2组成。在芬顿试剂的反应过程中，羟基自由基在铁离子的存在下迅速生成。该催化剂体系用于工业废水中有机污染物的处理是成功的。关于改善工业废水和垃圾渗滤液中复合废物的生物降解性和难降解性的预处理方法已有许多报道。由于芬顿体系的强氧化性，原来的污染物常常转化为CO2和H2O。近年来，芬顿体系与膜过滤、混凝等方法相结合，在很大程度上降解了有机物。此外，芬顿试剂在轻质醇和烷烃的氧化官能化中也是有效的，但选择性氧化的应用却很少。

芬顿体系具有良好的水溶性，地球上有丰富的亚铁离子。因此，可以使用该系统开发温和廉价的水相氧化工艺。尽管它有许多优点，但必须考虑到传统芬顿试剂的一个局限性：它的高氧反应性，常常导致深度氧化。将芬顿体系应用于化学合成中，最关键的问题是如何控制其反应性并提高其选择性。芬顿试剂的效率受pH值、Fe2 的反离子、溶剂、铁螯合物、UV和微波等因素的影响，从而控制Fe2 从Fe3 中的氧化反应性和再生能力。此外，还发现添加剂对改变芬顿体系的反应性起着至关重要的作用。例如，与KH2PO4作为添加剂的反应在苄醇的氧化中提供了高转化率和良好的选择性。

本研究的目的是控制芬顿体系的反应性，提高其选择性。通过对一系列添加剂的详细研究，发现芬顿体系的反应性可以很好地控制，苄醇氧化可以在室温下以良好的选择性进行。

二.实验过程

所有化学物质的纯度均在99%以上。一个典型的实验是在水浴中进行的。在玻璃反应器中加入乙醇（20mu;mmolL）、Fe SO4·7H2O（0.5mu;mmolL）和NHPI（0.5mu;mmolL）。将44 mmol/H2O2（30重量%的水，4.5毫升）加入注射器泵中，在30分钟内加入0.2毫升/分钟的速度，将反应混合物剧烈搅拌（约750mu;rpm）。用GC和GC-MS分析反应混合物。

然后，我们优化了反应条件（温度、浓度、铁盐和加入H2O2的速度）。

三.实验结果与讨论

3.1 不同添加剂的影响

结果表明，芬顿体系中的一些添加剂（如KH2PO4和KHSO4）能在70°C下产生更有效的氧化过程。KH2PO4的作用是控制溶液的pH值，改变溶液的pH值以产生羟基自由基。结果是，提高了反应的选择性。在这一思想的鼓舞下，我们尝试通过在芬顿体系中加入不同的无机缓冲液来进一步改善反应，研究了不同添加剂（NaBF4、NaH2PO4、KH2PO4、KHP）对70°C的影响。我们的结果与以前KH2PO4作为添加剂的报告非常接近。添加NaBF4、NaH2PO4或KHP似乎不能得到较好的结果。

由于在室温下进行反应有利于节约能源和开发安全的工艺所以我们在25℃下考察了这些无机缓冲液的性能。结果表明，这些催化剂体系在室温下的反应性较差。虽然可以获得良好的选择性，但转化率很低。增加反应时间或改变添加剂的量根本不能改善结果。虽然离子液体在改善氧化体系的反应性方面发挥了很好的作用，但似乎这种化合物与芬顿体系不能很好地配合。以[HMIM] [HSO4]（己基甲基咪唑硫酸氢盐）为添加剂，在25°C下转化率仅为1.3%，加入N1111GLY（甘氨酸四甲基铵）或N2111OAC（三甲基乙酸铵）可加速反应，但选择性也不好。

3.2 NHPI/FESO4氧化工艺

在水相中通过一系列的络合物反应生成羟基自由基，羟基自由基可以从醇中提取氢原子，形成烷基自由基。如果大量羟基自由基积累而不受控制，这可能导致深度和非选择性氧化。因此，我们认为至少有两种方法可以提高芬顿体系的反应选择性。一是控制羟基自由基的生成速率，另一方面是减少非选择性羟基自由基的积累，并将其转化为具有较高选择性的自由基，如邻苯二甲酰亚胺基氧基（PINO）被广泛应用于氧化反应中。加入无机缓冲液可以改变反应混合物的pH值，控制自由基的生成速率。这是上文提到的第一种方法，并且已经被广泛地研究。通过这种方式可以提高选择性，但该体系在室温下的催化活性很低。

到目前为止，还没有关于第二种方式的报道。如果可以开发一种方法来实现第二种方式，则应当提高选择性而不损失催化活性。该方法有两个成功的关键：一是添加剂主要存在于有机相中，避免添加剂对芬顿体系的影响；二是添加剂与羟基自由基反应生成高氧化自由基。N-羟基邻苯二甲酰亚胺（NHPI）是这两种限制条件下的优良选择，PINO自由基可由NHPI生成，已被证明是具有高氧化选择性的催化剂。

然后，我们研究了NHPI作为添加剂的作用。事实上，结果是令人满意的。加入NHPI后，选择性和转化率均有明显提高。2，2，6，6-四甲基哌啶氧基和4-OH-TEMPO（4-羟基-TEMPO）的反应速度也与无机缓冲液相比具有更好的转化率和选择性。然而，TEMPO或4-OH-TEMPO的转化率低于NHPI。在苯甲醇氧化反应中，鉴别了不同铁盐的反应活性。与Fe2（SO4）3、Fe（NO3）3·9H2O和FeCl 3相比，FeSO4·7H2O与NHPI的协同作用具有明显的选择性。

3.3不同醇的氧化反应试验

为了研究NHPI/FESO4/H2O2体系的普遍性，我们对不同醇的氧化进行了研究。这些氧化大部分都得到了良好的结果。其中，苄基醇在25℃下的结果令人满意，在25℃时，4-异丙基苄醇和alpha;-苯乙醇的转化率较低，这可能是由于给电子基团的取代引起的。alpha;-苯乙醇的转化率在55°C时达到50.5%，选择性良好。值得注意的是，邻位取代基和高分子基团也可以降低反应速率。4-甲氧基苄醇和4-甲基苄基醇由于熔点高，在55℃下进行试验，结果令人满意。然而，这种催化剂体系对2-丁醇氧化的选择性有点差。

四.结论

为了提高芬顿试剂（Fe2 /H2O2）在氧化反应中的选择性，我们研究了芬顿试剂与一系列添加剂的协同作用。结果表明，以NHPI为助催化剂，芬顿体系的反应性和选择性得到提高。这种新的Fe2 /H2O2/NHPI体系在不添加任何有机溶剂的条件下，可以很好地催化苄醇的氧化。此外，该催化剂体系对不同醇的氧化都是有效的。借此实验，我们希望在这里开发的催化剂体系可以为醇和类似化合物的氧化提供了绿色、无毒、廉价的新方法。

参考文献

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