关键词: 乙酰苯胺, 可视化, 固定床脱水回流装置, 乙酰氧基化反应, 恒pH滴定

Abstract:

In this study, the preparation method of acetanilide, which is commonly taught in current undergraduate experimental courses, is improved. While acetic acid and aniline were used as starting materials in the improved method, zinc powder was replaced with stannous chloride (which is listed as an easy-to-make tube explosion product) as a reducing agent to prevent aniline from being oxidized. At the same time, p-toluene sulfonic acid was added as a catalyst. A fixed bed dehydration reflux device was used instead of the classical fractionation device, and a packed rectification column was used as the fixed bed. The column was filled with glass spring packing, a 4A molecular sieve and color-changing silica gel from bottom to top in turn. During the reaction, distilled water and acetic acid were fractionated by the glass spring packing, acetic acid was refluxed to the reaction flask, and water was absorbed by the 4A molecular sieve and color-changing silica gel. After absorbing water, the color of the silica gel changed from orange to green, which is a clear indication of the reaction process. The improved experiment does not require control reagents, the reaction time is shortened, and the phenomenon is rich, making it more suitable for undergraduate teaching. In addition, two extended experiments were designed in this study, which can be selected according to the needs of teaching. One is to prepare phenyl 4-acetylaminoacetate from acetanilide; the second is to determine the unreacted aniline content in the waste liquid by constant pH titration. This modified experimental procedure employs extraction, column chromatography, titration, and data processing and analysis, which can effectively improve the comprehensive experimental ability of the students.

Key words: Acetanilide, Visualization, Fixed bed dehydration reflux device, Acetylation reaction, Constant pH titration