Sandmeyer Reaction桑德迈尔反应

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Sandmeyer Reaction(桑德迈尔反应)是一个重氮官能团在亚铜盐的催化下被卤素或氰基所取代的反应。和简单的卤化反应比较该反应的优势在于只有一种异构体形成。






其反应机理还没有完全搞清楚,一般我们认为是一个自由基反应,苯环上的取代基(如羟基,烷氧基,酰基,羧基,硝基和卤素等),无论是吸电子基团还是供电子基团,对反应都没有特别的影响,氯代必须用 CuCl/HCl 体系,溴代则要用CuBr/HBr 体系,碘代则一般用盐酸做重氮盐,不用Cu 盐催化,直接加KI或NaI 就能得到碘苯。

一百多年来,由于芳香重氮化合物活性高,容易制备,工艺成熟,使其在化学合成和化学工业中的应用非常广泛。Sandmeyer 反应,Gatterman 反应和Balz-Schiemann 反应是官能团转换的重要反应,也是经典的人名反应,见证了整个有机化学的发展历程。



A mixture of 127.5 g. (1 mole) of a good commercial grade of o-chloroaniline and 300 ml. (2.5 moles) of 48% hydrobromic acid in a 2-l. flask set in an ice bath is cooled to 0°C by the addition of ice. A solution of 70 g. (1 mole) of sodium nitrite in 125 ml. of water is added rapidly, with stirring, the temperature being kept below 10°C by the addition of small pieces of ice. When only about 5 ml. of the sodium nitrite solution remains, further additions are made cautiously until an excess of nitrous acid remains after the last addition.

In the meantime, a mixture of 79 g. (0.55 mole) of cuprous bromide (Note 3) and 80 ml. (0.6 mole) of 48% hydrobromic acid is heated to boiling in a 5-l. round-bottomed three-necked flask, equipped with a condenser set for distillation and provided with a 2 L receiving flask, a steam inlet tube closed by a screw clamp, and a separatory funnel. About one-fourth of the diazonium solution is transferred to the separatory funnel, without filtration, and immediately run into the cuprous bromide-hydrobromic acid solution, which is kept boiling over a free flame, at such a rate that boiling is continuous. When the separatory funnel is nearly empty a further portion of the cold diazonium solution is transferred to it without interrupting the addition. All the diazonium solution is added in this way over a period of about 30 minutes, during which time much of the product steam-distils. When the addition is complete, the stopcock in the separatory funnel is closed, the screw clamp in the steam line is opened, and a vigorous current of steam is passed through the mixture until no more organic material distill. About 1–1.5 L of distillate is collected. The heavy organic layer is separated from the distillate and washed with 10-ml. portions of concentrated sulfuric acid until the acid becomes only slightly colored during the washings; four washings usually suffice. The oil is then washed with one 100-ml. portion of water, two 50-ml. portions of 5% aqueous sodium hydroxide, and finally with one 100-ml. portion of water. The product is dried over about 3 g. of calcium chloride and distilled from a 250-ml. distilling flask. The yield of pure, colorless o-chlorobromobenzene, boiling at 199–201oC/742 mm., is 170–183 g. (89–95%).

【Hartwell, J. L.Organic Syntheses, Coll. Vol.3, p.185; Vol. 24, p.22.】