Diphenyliodonium iodide

Fit up a 1 -litre round-bottomed flask for steam distillation (Fig. II, 40,1) and place in it 22 g. of iodosobenzene (Section IV.25) made into a thin paste with water (1). Steam distil until almost all the iodobenzene has been removed (about 9 g.) cool the residue in the flask at once, filter the white solid with suction and dry in the air. Wash it with a little chloroform, filter with suction, and dry in the air upon filter paper. The yield is 10-5 g. It may be recrystallised from 800-900 ml. of water, lodoxybenzene melts with explosive decomposition at 237°, 

The following reactions will assist the student in the identification of halogenated aromatic hydrocarbons. 

For details of test, see under Alkyl Halides, Section III,42,(ii). 

Nitration products. Although no general method of nitration can be given, the following procedure is wddely applicable. 

---

The interaction of iodoaobenzene and iodoxybenzene in the presence of aqueous sodium hydroxide yields the soluble diphenyllodonium iodate (IV) upon adding potassium iodide solution, the sparingly soluble diphenyliodonium iodide (V), analogous to ammonium iodide is precipitated ... 

I) The filtrate contains some diphenyliodonium salts these may be recovered as the sparingly soluble diphenyliodonium iodide (about 8 g.) (Section IV,27) by the addition of potassium iodide. 

A colourless salt is precipitated from the alkaline filtrate (without the washings) by passing in sulphur dioxide, which serves to reduce the iodic acid produced. After the mixture has stood for some time, the salt, diphenyliodonium iodide, is collected at the pump and recrystallised from hot water. 

The basic function of the iodine in the iodonium bases, which correspond exactly to the ammonium, sulphonium, and oxonium bases, is most interesting. A molecule of diphenyliodonium iodide has the same atoms as two molecules of iodobenzene and decomposes on heating with liberation of heat (contrast other dissociations such as those of N204, NH4C1, PC15) into two moles of C8H8I. Test with a small sample in a tube. 

Diphenyliodonium Iodide.—Crystallises from alcohol in long, yellow needles M.P. 175°—176° on melting decomposes completely into iodobenzene. (B., 25, 3495 26, 1307, 1354 27, 506.)... 

The presence of an aroyl fragment in azomethine ylides obtained from opening of three-membered rings in the case of dipolarophiles with high LUMO (lowest unoccupied molecular orbital) energy or in the absence of an external dipolarophile can lead to the possibility of such unusual reactions as intramolecular 1,3-dipolar cycloaddition [80]. Examples of such reactions are the thermal isomerization of aroyl aziridines 63 into a pyrrole derivative 64 [81, 82] or into 2,5-diphenyloxazole 65 (in the presence of diphenyliodonium iodide) [83] (Scheme 1.16). 

DIPHENYLIODONIUM IODIDE (Iodonium Compounds, diphenyl—iodide)... 

Diphenyliodonium iodide is obtained when sulfur dioxide or aqueous potassium iodide is added to a solution containing di-... 

For use in the preparation of iodoxybenzene by the disproportionation method (p. 72) it is superfluous to dry the crude product and to wash it with chloroform to remove iodobenzene. The crude wet iodosobenzene may also be used directly for the preparation of diphenyliodonium iodide (p. 52), but it is desirable to assay the wet product by titration to determine the quantity of iodoxybenzene needed. 

The iodimetric method as described under iodosobenzene (p. 71) is applicable here. The crude product is satisfactory for the preparation of diphenyliodonium iodide (p. 52). 

---