ABSTRACT

The alkylation process involves two competitive paths of O- and C-alkylation and achieving better selectivity for desired products is a very challenging problem. The development of new process for synthesis of O-methylated products of phenol and dihydric phenols is a subject of high industrial and academic interest. Alkyl phenyl ethers, especially anisole and 4-methoxyphenol, have captivated significant interest due to their increasing applications in pharmaceutical industries. The main emphasis of the present review is to explore the recent development in two catalytic O-alkylation processes. The first process is O-methylation of phenol into anisole and another is selective mono O-methylation of hydroquinone into 4-methoxyphenol. The present article covers O-alkylation methods with methanol and dimethyl carbonate as alkylating agent over various acidic and basic catalytic systems. The catalyst systems analyzed involves Bronsted and Lewis acidic and basic ionic liquids, conventional acids, metal oxides, solid acid and basic catalysts, hydrotalcites, various zeolites and heteropolyacids. The mechanistic behavior of alkylation reactions in presence of different catalytic system is reviewed critically which is important to design new and/or modified catalyst in order to maximize the yield of desired product. Additionally, an influence of reaction parameters, role of catalyst and their active sites on product distribution is described. The review paper gives useful insight for researchers in the field of catalysis and reaction engineering of alkylation reactions. Understandings of the reaction pathways will help in developing reliable kinetic models necessary for process scale-up to industrial scale reactor system.

摘要

烷基化过程涉及O-和C-烷基化两条竞争路径，对所需产品实现更好的选择性是一个非常具有挑战性的问题。苯酚和二元酚的O-甲基化产物合成新工艺的开发是工业界和学术界高度关注的课题。烷基苯基醚，尤其是苯甲醚和 4-甲氧基苯酚，由于其在制药工业中的应用越来越多而引起了人们的极大兴趣。本综述的主要重点是探索两个催化O-烷基化过程的最新发展。第一个过程是将苯酚O-甲基化为苯甲醚，另一个过程是选择性单O-对苯二酚甲基化为4-甲氧基苯酚。本文涵盖O-以甲醇和碳酸二甲酯为烷基化剂在各种酸性和碱性催化体系下的烷基化方法。分析的催化剂体系涉及 Bronsted 和 Lewis 酸性和碱性离子液体、常规酸、金属氧化物、固体酸和碱性催化剂、水滑石、各种沸石和杂多酸。批判性地回顾了不同催化体系存在下烷基化反应的机械行为，这对于设计新的和/或改性的催化剂以最大化所需产物的产率是重要的。此外，还描述了反应参数、催化剂的作用及其活性位点对产物分布的影响。该综述论文为烷基化反应的催化和反应工程领域的研究人员提供了有用的见解。