Iodide, potassium reaction with aryl diazonium salts

Reaction of aryl diazonium salts with iodide ion (Section 22.17) Adding potassium iodide to a solution of an aryl diazonium ion leads to the formation of an aryl iodide. 

The reaction of an aryl diazonium salt with potassium iodide is the standard method for the preparation of aryl iodides The diazonium salt is prepared from a primary aro matic amine m the usual way a solution of potassium iodide is then added and the reac tion mixture is brought to room temperature or heated to accelerate the reaction... 

Let us now consider the formation of aryl iodides from aryl diazonium salts and potassium iodide in methanol (Singh and Kumar 1972a, 1972b). Electron-donor substituents decelerate the process as compared with benzene diazonium (the substituent is hydrogen), whereas electron acceptor substituents accelerate it. Oxygen inhibits the reaction, and photoirradiation speeds it up. As the authors pointed out, in the case of 4-nitrobenzene diazonium, the reaction leads not only to 4-iodonitrobenzene but also to nitrobenzene, elemental iodine, and formaldehyde. All of these facts support the following sequence of events ... 

An aryl diazonium salt is converted to an aryl iodide on reaction with potassium iodide. 

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. 

Solid diazonium salts are well suited for reactions in the solid state. They rapidly react with potassium iodide when coground in an agate mortar (without sharp edges ) and give a quantitative yield of the solid aryl iodide after... 

A second method for preparing aryl halides is the Sandmeyer reaction. During a Sandmeyer reaction, a diazonium salt reacts with copper (I) bromide, copper (I) chloride, or potassium iodide to form the respective aryl halide. The diazonium salt is prepared from aniline by reaction with nitrous acid at cold temperatures. 

A diazonium salt reacts with. sodium or potassium iodide to form an aryl iodide. This, too, is a useful reaction because aryl iodides cannot be produced by direct iodination with I2 and a Lewis acid catalyst, as Ig reacts too slowly (Section 18.3). 

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