Diphenyleneiodonium chloride

Diaryliodonium salts are industrially employed as photoinitiators in cationic polymerizations [8-10]. They have been employed as Lewis acids [11], as oxidants (via formation of phenyl radicals) [12, 13], and in the area of macromolecular chemistry [14, 15]. Furthermore, diaryliodonium salts show biological activity in various applications, usually because of their ability to act as radical initiators [3, 16]. Diphenyleneiodonium chloride (DPI) is a cyclic diaryliodonium salt which has found numerous biological applications, often as a NADPH oxidase inhibitor ([17] see also [20 0] in [18]). The applications outlined above do not involve arylations and are hence not covered in this chapter. 

The most important representative of cyclic iodonium salts, the dibenziodolium or diphenyleneiodonium (DPI) cation 238, known in the form of iodide, chloride, hydrosulfate, hexafluorophosphate, or tetrafluoroborate salts, can be obtained by three different procedures (A, B and C) summarized in Scheme 2.71. Method A, originally developed by Mascarelli and Benati in 1909 [355], uses 2,2 -diaminodiphenyl (235) as the starting material, which upon diazotization with sodium nitrite in a hydrochloric acid solution followed by potassium iodide addition, gives DPI 238 as iodide salt. A similar reaction starting from 2-amino-2 -iododiphenyl 236 affords DPI as hexafluorophosphate or tetrafluoroborate in excellent yields (Method B) [356]. The third method involves the peracetic oxidation of 2-iodobiphenyl (237) to an iodine(III) intermediate that then cyclizes in acidic solution (Method C) [357]. More recently, these methods were used to prepare the tritium labeled DPI and of its 4-nitro derivative [358]. 

The most important representatives of stable cycHc iodonium salts, dibenziodohum or diphenyleneiodonium (DPI) salts, have been prepared as the iodide 26, the hexafluorophosphate 28, the tetrafiuoroborate 29, and the chloride 31, and can be obtained by three different procedures... 

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