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。

反应机理：

从形式上相当于芳香亲核取代反应。实际可能由单电子转移机理完成，但不前尚未明确。

反应实例

芳香重氮盐的一系列转化：在CuCN作用下、可得到相应的苯腈。若用CuCl、CuBr处理，则能得到对应的卤代衍生物。和碘化钠加热则得碘代衍生物、由四氟硼酸银处理得到氟硼酸重氮盐，加热后得到氟代衍生物(Balz-Schiemann反应)。还有、加水或醇在加热条件下，可得到对应的酚、芳基醚类衍生物。用亚磷酸处理重氮盐则被氢取代。

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。

反应实例

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.】

本文非原创内容，版权归原作者所有