关键词: 对-硝基苯基-β-羟乙基砜, 对-（β-羟乙基砜）苯胺, 电化学还原, 硫酸钛

Abstract:

Para-ester is the most important intermediate for the preparation of ethylene sulfone type reactive dyes, which is usually used in the dyeing of cellulose fibers and synthetic fibers. P-(β-hydroxyethyl sulfone) aniline is an important intermediate for the synthesis of para-ester. In this paper, p-(β-hydroxyethyl sulfone) aniline was prepared by electrochemical method, having the advantages of simple process, mild reaction condition, less environmental pollution, easy reaction control and so on. It has strong development potential and industrial application prospect. The electrochemical reduction of p-nitrophenyl-β-hydroxyethyl sulfone on a lead plate electrode to prepare p-(β-hydroxyethyl sulfone) aniline was investigated, and the reaction was carried out in a two-cell cationic diaphragm electrolytic cell. The electrolysis parameters, such as current density, electricity quantity, temperature and concentration of sulfuric acid, were firstly optimized to achieve a desirable current efficiency and excellent yield of p-(β-Hydroxyethyl Sulfone) Aniline. Under the optimal conditions (current density: 300 A·m^-2, electricity quantity: 6.0 F·mol^-1, temperature: 70℃, sulfuric acid concentration: 1.5 mol·L^-1), the current efficiency and yield of the target reaction reached 92.7% and 93.0%, respectively. Moreover, the introduction of 2.0% mass fraction of titanium sulfate additive to the electrolyte could indirectly alleviate the problem of slow diffusion rate of raw material in the late stage of electrolysis, which, in turn, could further increase the yield to 97.8%. At the later stage of reaction, as the concentration of raw materials decreased, the difference between the concentration in the body solution and the electrode surface became smaller, and the diffusion rate of raw materials from the solution to the electrode surface became slower, resulting in a slow reduction reaction rate. After adding titanium sulfate, Ti⁴⁺ was mainly diffused to the electrode surface in the late reaction solution, and Ti³⁺ with strong reducing property was reduced on the electrode surface. The p-nitrophenyl-β-hydroxyethyl sulfone and hydroxylamine intermediate of low concentrations were reduced to p-(β-hydroxyethyl sulfone) aniline, thus, improved the yield and current efficiency. The reduction of p-nitrophenyl-β-hydroxyethyl sulfone to p-(β-hydroxyethyl sulfone) aniline was determined by cyclic voltammetry and high resolution liquid-mass spectrometry. First, p-nitrophenyl-β-hydroxyethyl sulfone was reduced to hydroxylamine intermediate by 4 electrons, and then hydroxylamine intermediate was further reduced to p-(β-hydroxyethyl sulfone) aniline by 2 electrons, and the whole reaction process was a 6-electron reaction. This method provides a new process route for the syntheses of p-(β-hydroxyethyl sulfone) aniline and para-ester, which is beneficial to solve for the problems of environmental pollution and high production cost in the current production process.

Key words: p-nitrophenyl-β-hydroxyethyl, p-(β-hydroxyethyl sulfone) aniline, electrochemical reduction, titanium sulfate