Potassium iodide, diazonium salt reaction

The relative lability of diazonium salts dictates that the modification reaction be carried out between 0-5°C and that whenever possible the counterion of the diazonium salt be an inert anion such as tetra-fluoroborate. Diazonium salts readily undergo solvolytic reactions when exposed to ambient temperatures in hydroxylic solvents. They easily lose molecular nitrogen and will react with any available nucleophilic anion. For example, in an aqueous solution of potassium iodide the following reaction will take place (eq. 5.4). 

The experimental conditions necessary for the preparation of a solution of a diazonium salt, diazotisation of a primary amine, are as follows. The amine is dissolved in a suitable volume of water containing 2 5-3 equivalents of hydrochloric acid (or of sulphuric acid) by the application of heat if necessary, and the solution is cooled in ice when the amine hydrochloride (or sulphate) usually crystallises. The temperature is maintained at 0-5°, an aqueous solution of sodium nitrite is added portion-wise until, after allowing 3-4 minutes for reaction, the solution gives an immediate positive test for excess of nitrous acid with an external indicator—moist potassium iodide - starch paper f ... 

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... 

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. 

Iodine reacted with the indazole silver salt to give 3-iodoindazole. Reaction of potassium iodide with indazole diazonium salts has been reported on a number of occasions [67HC(22)1 90AHC(48)65]. 

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 ... 

N-Acetyl-2,5-dimethoxy-4-iodophenylisopropylamine. 5 g of the diazonium salt is prepared as described immediately above and cooled to 0° then added gradually to a solution of 8 g of potassium iodide in 10 ml of water. After reaching room temp the reaction is set until the evolution of nitrogen has stopped. The dark brown viscous semi-solid that will separate is dissolved in ethanol with heat and then eooled. On cooling the title material separates out and is crystallized from ethanol. Yield 1.97 g, mp 167-168°. 

Displacement of nitrogen from diazonium salts derived from 4- or 5-aminotriazoles can be achieved in the same manner as for other aromatic diazonium salts for example, diazotization of 4-amino-triazole-5-carboxamide and reaction with iodine and potassium iodide gives the 4-iodo derivative. ... 

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... 

Again the Sandmeyer reaction is frequently used to convert amino- to halo-isoquinolines. The diazonium salt of 5-amino-8-isoquinolinol (14) on treatment with potassium iodide and iodine gives the 5-iodophenol (15). Iodination of the hydrochloride of (15) with iodine monochloride in ethanol gives (16 Scheme 9) (66JMC46). 

Keywords solid diazonium salt, potassium iodide, iodination, solid-solid reaction, aryl iodide... 

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

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. 

Reaction of (2-methyl-5-)- and (2-methyl-6-benzothiazoIyl)-dimethyltriazene or 2-methyl-5- and 2-methyl-6-benzothiazolyl-diazonium salts with ferrocene gave 136 (R = ferrocenyl, R = H R = H, R = ferrocenyl, respectively).121 Use of the diazonium salts also led to the isolation of some 1,1 disubstituted ferrocenes in this reaction. The compounds 136 were used to prepare thiacyanines. Reaction of ferrocenecarboxaldehyde with the ethiodide of 2-methyI-benzothiazole followed by treatment with potassium iodide gave 137.121... 

Copper(I) iodide is unsatisfactory for use in the Sandmeyer reaction because of its insolubility. The iodo group is introduced by warming the diazonium salt solution in aqueous potassium iodide solution (Scheme 8.17). This method is one of the best means of introducing iodine into an aromatic ring. A one-electron reduction by the iodide ion is thought to initiate a radical reaction in a similar way to the Cu(I) ion. 

Salts of primary aromatic amines react with nitrous acid to produce diazonium salts. The reaction is usually performed by adding a cold solution of sodium nitrite to a cold solution of the arylamine in aqueous mineral acid. The end point of the reaction is conveniently determined by the detection of excess nitrous acid with potassium iodide-starch paper. Sulfamic acid has long been used both in industry and in the laboratory to remove excess nitrous acid. It has been found to react with the more active diazo compounds. In most cases, high temperatures are avoided to prevent the formation of phenols and the decomposition of the unstable nitrous acid. An excess of mineral acid is necessary to prevent coupling between the diazonium salt and unreacted amine (cf. method 494). If the amine salt is somewhat insoluble, a fine crystalline form, which is produced by rapid crystallization from a warm aqueous solution, may be employed. ... 

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). 

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. 

Introduction. The diazo group, N2X, is easily replaced by a number of other functional groups, such as OH, Cl, Br, I and CN. This affords a convenient method for the preparation of such derivatives as cannot be obtained by other methods except with great difficulty. The replacement of N2X by a halogen group is accomplished by heating the solution of diazonium salt with cuprous halide (Sandmeyer reaction) or with finely divided copper (Gatterman reaction). In the preparation of iodides the catalytic effect of copper is not required it is necessary only to pour the diazonium salt into a solution of potassium iodide and then to acidify the solution ... 

Copper(I) iodide is unsatisfactory for use in the Sandmeyer reaction because of its insolubility. The iodo group is introduced by warming the diazonium salt solution in aqueous potassium iodide solution (Scheme... 

Reaction of 6-aminodihydrodiazepinium salts with sodium nitrite and acid produced stable solids with peaks in their IR spectra at 2200 cm-1 characteristic of aromatic and heteroaromatic diazonium salts.28 64,55 These diazonium salts could be converted into 6-chlorodihydrodia-zepines.28,64,55 With alcohols or potassium iodide the diazonium group was replaced by a hydrogen atom in the latter case it is likely that a 6-iodo compound was formed which was then protodeiodinated in the acid conditions.54... 

---