Sandmeyer-Gattermann Reaction

The interesting research of Votocek, Zenisek 4 and Sebor 5 may also be referred to in this connection. This permits the Sandmeyer-Gattermann reaction (substitution of the diazo-group by chlorine and bromine) to be carried out electrolytically. For this purpose the diazotized solution of the amine is electrolyzed —for instance 50 g. aniline, 120 g. HC1, 38.5 g. NaN02—between copper electrodes with addition of cuprous chloride or copper sulphate. At the end of the experiment (ceasing of the nitrogen... 

The yields by the Gattermann reaction are usually not as high as those by Sandmeyer s method. Copper powder is also employed in the preparation of sulphinlc acids, for example ... 

Some of the cuprous chloride compounds of the diazonium salts have been isolated and analysed, and coirespond to the formula CoH.-.NjCl.CuoCIo (Hantzsch). The formation of a crystalline copper compound is rendeied very evident in the present preparation.. A modification of Sandmeyer s reaction IS the introduction of precipitated metallic copper in place of the cuprous salt (Gattermann). 

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. 

The yield in Sandmeyer reaction is found to be better than Gattermann reaction. 

The yields in the Gattermann reaction, however (e.g. o-bromotoluene, Expt 6.74), are usually not as high as those obtained by the Sandmeyer method. Copper powder is also employed in the preparation of sulphinic acids (e.g. benzenesul-phinic acid, Expt 6.75) which are obtained when a solution of a diazonium sulphate is saturated with sulphur dioxide and decomposed by the addition of copper powder. 

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. ... 

Gattermann Reaction.—The reaction was further modified by Gat-termann who found that finely divided metallic copper could be used with even greater advantage. The Sandmeyer and Gattermann reactions are not applicable, however, for the formation of the iodine products. To form these the diazonium salt, usually the acid sulphate, is heated with a solution of potassium iodide. 

Table I, which summarizes our preliminary survey of the reaction process, clearly shows the similarity of the Sandmeyer and Gattermann reactions to the hypophosphite and phosphite reductions studied by Kormblum and indicates that substituent groups facilitate these reactions in the sequence p-NOi > p-Cl > H > p-MeO, which is that for electron withdrawal from the nitrogen center, i.e., exactly what would be expected of an electron transfer to aryl ...

Preparation of Chlorine Derivatives by the Sandmeyer and Gattermann Reactions ... 

Treatment of diazonium salts with cuprous, Cu(I), salts generates aryl halides. When 398 reacts with CuCl (cuprous chloride) or CuBr (cuprous bromide), the products are chlorobenzene or bromobenzene via what is probably a radical reaction.29l jhis conversion is known as the Sandmeyer reaction. 2 The use of copper powder rather than cuprous salts for this transformation is often called the Gattermann reaction. 93,292b,c Aryl iodides are also produced from diazonium salts by reaction with potassium iodide (KI) but the actual reactive species may be l3-.294,295 Treatment of aniline derivative 403 with sodium nitrite and HCl followed by treatment with KI, for example, gave a 89% yield of 404.Aryl nitriles are generated under Sandmeyer conditions using cuprous cyanide (CuCN), as in the conversion of 405 to benzonitrile derivative 407 via diazonium chloride, 406. 

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. 

Sandmeyer Reaction Gattermann Reaction Korner-Contardi Reaction... 

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) ... 

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. 

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. 

The Sandmeyer procedure and its Gattermann variant (see page 259) often give poor yields when applied to diphenylamines, naphthylamines, or phen-anthrenamines, but good results can be obtained by the method worked out by Schwechten1239 as a variant of the Schiemann reaction (thermal decomposition of diazonium fluoroborates, see below). 

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... 

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