Sandmeyer reaction variations

Gattermann s reaction A variation of the Sandmeyer reaction copper powder and hydrogen halide are allowed to react with the diazonium salt solution and halogen is introduced into the aromatic nucleus in place of an amino group. 

Equally, all the attempts of Haginiwa to diazotize 2-amino-4-methylselenazole led to complete decomposition. Later these investigations were taken up by Metzger and Bailly. They tried to prepare selenazoles unsubstituted in the 2-position by means of diazo-tization and a special Sandmeyer reaction. In spite of variations in the reaction conditions, they were not able to deaminate 2-amino-4-phenylselenazole by this method. 

The replacement of the diazonium group by chlorine or bromine is accomplished using the Sandmeyer reaction Replacement with fluorine and iodine can be achieved by variations of this reaction. 

For the preparation of chlorides or bromides, the diazonium salt is decomposed with a solution of cuprous chloride or bromide in the corresponding halogen acid (Sandmeyer reaction). It is possible to prepare the aryl bromide from the diazonium chloride or sulfate. A variation Involves the use of copper powder and a mineral acid for the decomposition step (Gattermann reaction). Both procedures are illustrated by the syntheses of the isomeric bromotoluenes and chlorotoluenes. The usual conditions of the Sandmeyer reaction fail in the preparation of the chloro- and bromo-phenanthrenes. However, these compounds can be successfully obtained by the interaction of the diazonium compound with mercuric and potassium halides (Schwechten procedure). Another procedure for formation of aryl bromides involves treatment of the amine hydrobromide with nitrogen trioxide in the presence of excess 40% hydro-bromic acid. The Intermediate diazonium perbromide is then decomposed by heat. ... 

The Cu(I)/Cu(II) couple is utilised in the Sandmeyer reaction, in which an aromatic diazonium salt is converted into the corresponding aryl chloride by the catalytic action of Cu(I)Cl. There is a variation that uses copper and HC1, which is called the Gatterman reaction. 

C6H5N2 + Cl- C HjCl + N2 This reaction was discovered by the German chemist Traugott Sandmeyer (1854-1922) in 1884. A variation of the reaction, in which the catalyst is freshly precipitated copper powder, was reported in 1890 by the German chemist Ludwig Gatterman (1860-1920). This is known as the Gatterman reaction (or Gat-terman-Sandmeyer reaction). 

Gattermann reaction A variation of the Sandmeyer reaction for preparing chloro-or bromoarenes by reaction of the diazo-nium compound. In the Gattermann reaction the aromatic amine is added to sodium nitrite and the halogen acid (10°C), then fresh copper powder (e.g. from Zn + CuSOJ is added and the solution warmed. The dia-zonium salt then forms the haloarene, e.g. 

This variation of the Sandmeyer reaction (developed by T. Cohen, University of Pittsburgh) is a much simpler and safer procedure than an older method for phenol preparation, which required heating the diazonium salt with concentrated aqueous acid. 

Another common transformation of diazonium salts is their conversion to aryl halides by reaction with cuprous salts (CuX), in what is known as the Sandmeyer reaction, named after Traugott Sandmeyer (Switzerland 1854-1922). This means that the Ar-NH2 ArX conversion is possible, where Ar = an aryl group. When 132 is treated with cuprous bromide (CuBr), the product is bromobenzene (18). The reaction works with many other cuprous salts as well, including cuprous chloride (CuCl). A variation of this reaction treats the diazonirun salt with cuprous cyanide (CuCN) to give a nitrile. In this manner, 4-methylanihne (24) is treated with HCI and NaN02 and then with CuCN to give 4-methyl-l-cyanobenzene (134). 

This particular variation of the Sandmeyer reaction is useful because it allows the conversion of an aromatic amine, readily available by reduction of the corresponding nitro compound, to a reactive carbon substituent. This substitution involves replacement of the C—N bond with a C—C bond. 

The diazonium ion is important because it is the critical intermediate in a number of transformations lumped under the heading of the Sandmeyer reaction, named for Traugett Sandmeyer (1854-1922). Cuprous salts convert a diazonium ion into the related cyanide or halide. In recent times, numerous variations on the basic theme of the Sandmeyer reaction have improved yields and reduced side products. Figure 14.54 shows three typical Sandmeyer reactions. 

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