Phosphorus triiodide iodination

Under high pressures and temperatures, iodine reacts with oxygen to form iodine pentoxide [12029-98-0] (44). The reaction of iodine with carbon monoxide under acidic conditions is catalyzed by palladium salts (45). Phosphorous vapor and iodine react to form phosphorus triiodide [13455-01-1]> PI3 (46). 

The aliphatic iodine derivatives are usually prepared by reaction of an alcohol with hydroiodic acid or phosphorus triiodide by reaction of iodine, an alcohol, and red phosphorus addition of iodine monochloride, monobromide, or iodine to an olefin replacement reaction by heating the chlorine or bromine compound with an alkali iodide in a suitable solvent and the reaction of triphenyl phosphite with methyl iodide and an alcohol. The aromatic iodine derivatives are prepared by reacting iodine and the aromatic system with oxidizing agents such as nitric acid, fuming sulfuric acid, or mercuric oxide. 

Phosphorus triiodide is not sufficiently stable to be stored, but it can be generated in situ (in the reaction mixture) by the reaction of phosphorus with iodine. 

Or the water may be allowed to drop on to phosphorus triiodide or on to a mixture of phosphorus and iodine.3,4 The preparation of a small quantity is most conveniently effected as follows —... 

Phosphorus Triiodide.—When solutions of iodine and phosphorus in CS2, in the proportions of 31 to P, are mixed, a red colour appears and on cooling dark red needles separate.12... 

Acyl Radical.—The names of the acid chlorides are derived from the names of the acids by changing the termination ic to yl. Thus, CHa—CO—Cl is acetyl chloride or ethanoyl chloride. The acid chlorides of the lower acids are liquids which possess a very penetrating and disagreeable odor and boil at a lower temperature than the corresponding acid. Analogous compounds of bromine and iodine are formed by the action of phosphorus tri-bromide or phosphorus triiodide on the acids. These are ... 

The products are evidently determined by the thermodynamics of the reaction reactions of alkyl iodides with phosphorus diiodide or with equivalent mixtures of phosphorus and phosphorus triiodide give essentially identical results (19). Such reactions with simple alkyl iodides (methyl to pentyl), however, require temperatures in the range 200-220°. While good yields are generally obtained, the advantage of added iodine is uncertain. 

Preparation.—By the decomposition of phosphorus triiodid by water Pis -j- 3HsO = HsPOs -I- SHI. Or, in solution by passing hj drogen sulfld through water holding iodin in suspension HsS-f-Is = 2HI-f S. 

What if, instead of a bromoalkane, we want the corresponding iodoalkane The required phosphorus triiodide, PI3, is best generated in the reaction mixture in which it will be used, because it is a reactive species. We do this by adding red elemental phosphorus and elemental iodine to the alcohol (margin). The reagent is consumed as soon as it is formed. 

The observations of C. L. Gazzaniga,1 A. Schrotter, and T. S. Traill were treated in connection with the action of iodine on phosphorus. Some indefinite iodides were mentioned by F. Wohler, J. L. Gay Lussac, C. M. van Dijk, R. Boulouch, K. I. Lissenko, and F. Sestini. The two best defined iodides are the diiodide and triiodide while the existence of the tetritaiodide, the tetratritaiodide, and of the pentaiodide is not so well established. According to R. Boulouch, where dry iodine is added to a soln. of phosphorus in dry carbon disulphide in quantity less than is... 

The reaction very likely proceeds through the disproportionation of 4-ethoxyphenyl tellurium monochloride to tellurium and the diaryl tellurium dichloride. Bis[trifluoromethyl] tellurium transferred its trifluoromethyl groups to iodine, sulfur, selenium, phosphorus, arsenic, and antimony on heating with the elements, sulfur dichloride, selenium tetrabromide, or the triiodides of phosphorus, arsenic, and antimony at 170 to 220° in sealed tubes3. 

Phosphorus reacts energetically with iodine when heated in contact with it, or in dry organic solvents, giving orange to red crystalline products. Two of these, the diiodide and the triiodide, have been prepared by various reactions, and their properties well ascertained. 

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