实验三 苯亚甲基苯乙醛酮(查尔酮)的制备

实验三 苯亚甲基苯乙醛酮（查尔酮）的制备
[实验目的] 了解Aldol 缩合反应的机理、特点及反应条件。

[反应式]
2CHO COCH 3C H C H C O
+
[试剂]
苯甲醛：4.6 g
苯乙酮：5.2 g
乙醇（95 %）：15 mL
氢氧化钠：2.2 g （溶于20 mL 水）
[实验操作]
在配有搅拌、温度计、回流冷凝器及滴液漏斗的100 mL 的三颈瓶中，加入氢氧化钠水溶液、乙醇（95 %）15 mL 及苯乙酮5.2 g ，水浴加热到20℃，滴加苯甲醛4.6 g ，滴加过程中维持反应温度20-25℃，加毕，于该温度下继续搅拌反应0.5 小时，加入少量的查尔酮做晶种，继续搅拌1.5 小时，析出沉淀，抽滤、水洗至洗水呈中性，抽干得粗产品，以乙酸乙酯为溶剂重结晶，得精品为浅黄色针状结晶，熔点：55-56℃。

[思考题]
1． 本实验中可能的副反应有哪些？怎样可以避免？
2． 为什么该产品析晶较困难？
[参考文献]
[1] 胡志国等，化学研究与应用，2004，16（4），583-584
The preparation of Benzalacetophenone(Chalcone)
［Aim ］
To comprehend the mechanism, characteristics and reaction conditions of Aldol reaction. ［Reaction equation ］
NaOH
2CHO COCH 3C H C H C O +
［Reagents ］
Benzaldehyde: 4.6 g
Acetophenone: 5.2 g
Ethanol(95%): 15 mL
Sodium hydroxide: 2.2 g (in 20 mL of water)
［Procedure ］
In a 100 mL three-neck flask equipped with an efficient stirrer, thermometer, dropping funnel and reflux condenser, place aqueous solution of sodium hydroxide, 15 mL of ethanol (95%) and 5.2 g of acetophenone. Heat this solution to 20℃, and add 4.6 g of benzaldehyde slowly with stirring, keeping the reaction temperature 20-25℃, and continue stirring 0.5 h after addition at this temperature. Inoculate the mixture with a little powdered benzalacetophenone and continue stirring for additional 1.5 h. The crude product is separated by filtration and washed with water. After recrystallization from ethyl acetate, the fine product is obtained, m.p 55-56℃. ［Subjects for Thinking ］
1. Point out the side reaction in this preparation? How can we avoid it?
2. Please explain the reason why the precipitation process of the product would be difficult.
Reference
[1] HU Zhi-Guo etal, Chemical Research and Application, 2001，16（4），583-584。