不用過柱子！乙二醇助你輕松除勞森試劑副產物

用過勞森試劑的小伙伴一定印象深刻，一方面被其難聞的氣味“勸退”，另一方面被其副產物難以除去而困擾，經常和產物極性接近，過柱子又很容易拖尾，真是欲哭無淚啊。難聞的氣味咱可以忍忍，但純化困難是真的忍不了啊！別急，小編在瀏覽文獻發現一篇文章分享了他們使用乙二醇和水加熱攪一攪然后分液的方法，成功除去了勞森試劑反應后的副產物，無需過柱子，Wonderful!

下面讓我們一起看看這篇文章：

文章首先分析了勞森試劑發生硫代反應后的副產物A，副產物A的極性常常和硫代產物極性接近，分離困難。

有文獻報道用碳酸氫鈉溶液可以將副產物A轉化為水溶性的B,進而通過萃取除去雜質( 這個方法小編試過，對小編的硫代酰胺反應無效 )，然而這種方法會產生大量含磷廢水。

而本文作者將乙二醇和水加入勞森試劑硫代反應后( 甲苯為溶劑 )的體系，加熱將副產物A轉化為大極性的C2( C2含有兩個羥基 )，分液后C2在乙二醇相，硫代產物在甲苯相，輕松完成副產物的分離，大功告成。( 小編親測有效，兩相都點過板，分的很干凈 ）

詳細步驟如下，他們還通過后續的重結晶，除色等操作完成了40 g規模的純化。

To a 500 mL three-necked flask 40.1 g of N2,N6-bis(2,4,6-trimethylphenyl)pyridine-2,6-(carbothioamide)(5, 0.10 mol), 41.2 g of Lawesson’s reagent(0.051 mol), and 200 mL of toluene were added. The mixture was heated to reflux under a nitrogen atmosphere. TLC monitoring showed that there still existed some amide-thioamide intermediate after 5 h and heating was continued for another 3 h. Afterwards, TLC monitoring showed that the amide-thioamide had nearly disappeared. Then, to the cooled mixture, were added 100 mL of ethylene glycol (excess), together with 1.0 mL of water and the resulting mixture was stirred at 95 °C. TLC monitoring of the toluene layer showed that the byproduct A of the Lawesson’s reagent had disappeared after 7.5 h. The slightly cooled mixture was transferred to a separation funnel. The toluene layer was separated, and the ethylene glycol layer and 50 mL of toluene were transferred back to the flask and stirred at 95 °C (oil bath) for 30 min. The toluene layers were combined, part of the solvent removed under reduced pressure and the remaining solution was heated to reflux and diluted with 100 mL of heptane. The solution remained clear during reflux. Then, the solution was cooled to precipitate the crystalline solid that was collected by filtration and washed with heptane (100 mL). Then, the solid was treated with 200 mL of toluene and 5.0 g of activated carbon at 80 °C, followed by hot filtration. The filtrate was concentrated to afford 39.5 g of the desired dithioamide 6 (91%) as bright yellow crystalline solid.

原文出處

Beilstein J. Org. Chem. 2021, 17, 805–812.