Sandmeyer reaction

Through a Sandmeyer reaction, named after their discoverer Traugott Sandmeyer (1854 - 1922), the amino group of an aromatic compound is substituted by a nucleophile by means of a diazotization. The reaction is very suitable for the chlorination and bromination of aromatic compounds, and is used when the substituent, such as bromo, can not be introduced by simply boiling down of the diazonium salt in the aromatic nucleus. Nitriles and aryl mercury compounds can be represented by a Sandmeyer reaction.

For fluorination she is ill suited, so instead the Schiemann reaction is employed. The iodination occurs, however, on a sand- meyer- like reaction ( see below).

The Rosenmund -von Braun reaction for the preparation of aryl nitriles resembles the Sandmeyer reaction.

Reaction

The aromatic amine is added in the cold with nitrite and the nucleophile (→ X). The reaction takes place with the aid of the corresponding copper (I ) salts as catalysts. The following reaction scheme shows the implementation of the diazonium ion with chloride as the nucleophile:

Mechanism

The mechanism of this reaction according to the diazotization is not yet fully understood. It is believed that the resulting diazonium compound with the oxidation of a reduced -to bivalent copper (SET = " single electron transfer "). With elimination of N2 is an aryl radical (Cl -, Br -, CN - ) combines with the anion of the copper salt, the nucleophile forms. Here, the Cu ( II) via a further one-electron transfer to Cu again (I ) is reduced, so that the catalyst is recovered.

By the formation of biphenyl as a by- product of the dimerization reaction is a free-radical mechanism is plausible. Other by-products can also be phenols, diaryls and azo compounds. The copper serves only as an electron - donator or. Alternative representations of the mechanism, however, assume a bond between the copper (II ) salt to the aryl radical and subsequent Halogenidtransfer of copper.

Sandmeyer reaction analogous

Although this reaction is not one of the Sandmeyer reactions forming aryl diazonium salts with sodium nitrite in an analogous manner nitroaromatics. The copper ( I) salt is, however, in this case formed in situ by a redox reaction with sodium nitrite in a copper ( II) salt. The nitrite thus serves both as a nucleophile as well as a reducing agent.

Sandmeyer -like reaction

The iodination of aromatic compounds is by reaction of aryl diazonium salts with potassium iodide also possible. In this case, the nucleophile itself iodide, and the resulting iodine species take over the function of the otherwise copper (I) used catalyst. In the reaction is a free radical chain reaction, the chain carrier is an iodine radical anion. The reaction is initiated with the reduction of the diazonium ion by iodide.

Start reaction:

Chain reaction: