1858 年，Peter Griess首次发现了芳香重氮化合物。1884 年，德国化学家T.Sandmeyer在用乙炔铜和苯胺的重氮盐（PhN2Cl）合成苯乙炔时，得到的主产物却是氯苯，经过仔细研究，发现原来是由于反应中产生的CuCl催化使重氮基被氯取代。随后，Sandmeyer发现用CuBr和CuCN也能得到相应的溴苯和苯甲腈，因 此我们把这一类反应称为Sandmeyer反应。1890 年，L.Gatterman发现直接用铜粉和盐酸或氢溴酸也能从苯胺得到相应的氯苯或溴苯，这种类型的反应称为 Gatterman反应。1927 年，同样是德国的化学家G.Balz和G.Schiemann发现直接 加热苯胺的硼氟酸重氮盐能得到氟苯，这就是Balz-Schiemann反应。1935 年， F.B.Dains 和 F.Eberly用KI去处理重氮盐，成功合成了碘代苯。随后重氮化羟基取代和重氮化去胺反应也相继被发现，加上偶氮反应，形成了比较完善的芳香重氮化合物反应体系。

      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。 

1、重氮化氯代 

     芳胺的盐酸重氮盐在氯化亚铜的催化下发生反应从而得到相应的氯代产物，胺基取代的芳杂环也能发生相同的反应。这是合成芳香氯代物的重要的方法，一般的转换过程是对底物硝化，还原为胺，再重氮化氯代，这个方法特别适用于将氯原子引入用其他方法难以引入的位置。反应收率通常还可以。 

       A solution of 450 g. (2 moles) of stannous chloride crystals in 600 cc. of concentrated hydrochloric acid is placed in a 3-l. beaker provided with an efficient mechanical stirrer and cooled in an ice bath. When the temperature of the solution has fallen to +5°, 100 g. (0.66 mole) of m-nitrobenzaldehyde is added in one portion. The temperature rises slowly at first, reaching 25–30° in about five minutes, then rises very rapidly to about 100°. Stirring must be vigorous or the reaction mixture may be forced out of the beaker. During the reaction the nitrobenzaldehyde dissolves, and an almost clear, red solution is obtained. The solution is cooled in an ice-salt mixture until the temperature has fallen to about +2°. During the cooling, orange-red crystals separate and a pasty suspension results. 

      A 250-cc. separatory funnel is fixed so that its stem extends below the surface of the pasty suspension. A solution of 46 g. (0.67 mole) of sodium nitrite in 150 cc. of water is placed in the funnel and is slowly added to the well-stirred mixture until it shows a positive starch-iodide test for nitrous acid. The temperature of the mixture is maintained between 0° and +5°throughout the addition of the nitrite solution, which requires about ninety minutes. Usually, all but 5–8 cc. of the nitrite solution must be added before a positive test for nitrous acid appears. 

    During the latter part of the diazotization of the aminobenzaldehyde, a hot solution of cuprous chloride is prepared. In a 5-l. round-bottomed flask, 189 g. (0.75 mole) of powdered copper sulfate crystals and 161 g. of sodium chloride are dissolved in 600 

cc. of hot water, and to this solution is added a solution of 41 g. (0.22 mole) of sodium metabisulfite (Na2S2O5) and 27 g. (0.67 mole) of sodium hydroxide in 300 cc. of water. The final temperature of the resulting cuprous chloride solution should be about 75°. 

    The diazonium solution is added to the hot cuprous chloride solution while the latter is shaken by hand but is not cooled. After the solutions are thoroughly mixed, 840 cc. of concentrated hydrochloric acid is added and the mixture is allowed to stand overnight. The reaction mixture is steam-distilled to separate the m-chlorobenzaldehyde, which is collected practically completely in the first 1.5 l. of distillate. The m-chlorobenzaldehyde is removed from the aqueous distillate by extraction with two 150-cc. portions of ether, and the ethereal solution is dried with 10–15 g. of anhydrous calcium chloride. After being decanted from the drying agent, the ether is distilled, and the residual liquid is distilled under diminished pressure. The m-chlorobenzaldehyde boils at 84–86°/8 mm., 107–109°/26 mm. The yield is 70–74 g. (75–79 per cent of the theoretical amount).