SANDMEYER-GATTERMANN Aromatic

SANDMEYER GATTERMANN Aromatic substitution Substitution of an amine group via the diazonium sait by nucleophiles such as cr, Br, c. CN-R-S", HO, some via cuprous salt catalysis. 

Substitution of an aromatic amino group by fluorine via a diazonium salt using fluoroborates (compare Sandmeyer- Gattermann) (see 1st edition). 

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. 

When aqueous solutions of aromatic and heteroaromatic diazonium salts are treated with cuprous chloride, -bromide, or -cyanide, the corresponding aromatic chlorides, bromides, or cyanides are formed, respectively. In many cases the anions mentioned must be present in excess. This reaction, the Sandmeyer reaction, was discovered by Sandmeyer in 1884. A variant carried out with copper powder and HBr or HC1 was for many years called the Gattermann reaction (Gattermann, 1890). As it is often confused with the Gattermann-Koch reaction (ArH + CO + HC1 ArCHO), and as it is mechanistically not significantly different from Sandmeyer s procedure, the name Gattermann reaction should be avoided. 

Reaction XLIX. (b) Action of finely divided Copper and Alkali Cyanides on Aromatic Diazonium Compounds (Gattermann). (B., 23, 1218.)—This is the Gattermann modification of the preceding Sandmeyer reaction as usual, the cuprous salt is replaced by finely divided copper. This method gives better yields of some aromatic nitriles. 

For introduction of SCN into aromatic compounds the Sandmeyer reaction or its Gattermann variant is much more widely applicable than direct replacement of H by SCN (see page 202). An aqueous thiocyanate solution and CuSCN are added to a diazonium salt solution prepared in the usual way, or the addition is made gradually in the reverse direction — the diazonium salt to an aqueous solution of K3[Cu(SCN)4] copper powder can also be used.1264-1266 Reaction, with evolution of nitrogen, often occurs at room temperature or on... 

This reaction was initially reported by Gattermann in 1890. It is the preparation of aromatic halides or aromatic cyanides by decomposition of corresponding diazo salts in the presence of copper powder, in which copper powder is freshly obtained from a copper (II) sulfate aqueous solution. Therefore, it is generally known as the Gattermann reaction. Occasionally, it is also referred to as the Gattermann method. It should be pointed out that this reaction is almost equivalent to the Sandmeyer Reaction It is believed that a radical mechanism might be involved in this reaction, by which electron transfer occurs at the surface of metallic copper. However, this reaction is not applicable for the preparation of aromatic fluorides because HF exists as H2F2 and ionized as H+ and 10 2 . ... 

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. 

Substitution of diazonium groups in aromatic compounds by halo or cyano groups in the presence of cuprous salts (Sandmeyer reaction), copper powder and hydrochloric or hydrobromic acid (Gattermann reaction) or cupric salts (Komer-Contardi reaction) ... 

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