Phosphorus triiodide preparation

Phosphorus triiodide [ 13455-01-1 ] M 411.7, m 61 . Decomposes in moist air and must be kept in a desiccator over CaCl2. It is crystallised from sulfur-free CS2 otherwise the m decreases to ca 55°. It is best prepared freshly. [J Am Chem Soc 49 307 7927 Handbook of Preparative Inorganic Chemistry (Ed. Brauer) vol I 541 7965.] HARMFUL VAPOURS. 

A student prepares phosphorous acid, H3PQ3, by reacting solid phosphorus triiodide with water. 

Although 1,3,2-diazaphospholenium cations are usually prepared from neutral NHPs or 1,3,2-diazaphospholes via Lewis-acid induced substituent abstraction or A-alkylation, respectively (cf. Sect. 3.1.2), the group of Cowley was the first to describe a direct conversion of a-diimines into cationic heterocycles by means of a reaction that can be described as capture of a P(I) cation by diazabutadiene via [4+1] cycloaddition [31] (Scheme 4). The P(I) moiety is either generated by reduction of phosphorus trihalides with tin dichloride in the presence of the diimine [31] or, even more simply, by spontaneous disproportionation of phosphorus triiodide in the presence of the diimine [32], The reaction is of particular value as it provides a straightforward access to annulated heterocyclic ring systems. Thus, the tricyclic structure of 11 is readily assembled by addition of a P(I) moiety to an acenaphthene-diimine [31], and the pyrido-annulated cationic NHP 12 is generated by action of appropriate... 

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. 

Hydrogen bromide and hydrogen iodide may readily be prepared by the hydrolysis of phosphorus tribomide and phosphorus triiodide, respectively ... 

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 —... 

Iodopyrazine and six mono- and dialkyl- and phenyl-substituted 2-iodopyrazines have been prepared (30-60% yield) by displacement of the chloro substituent from the corresponding chloro compounds with a solution of sodium iodide and hydriodic acid in ethyl methyl ketone (887). Attempts to prepare iodopyrazine by treating the hydroxypyrazine with phosphorus triiodide were unsuccessful (887). 

P-P-salts can be isolated from hydrolyzates of phosphorus tribromide or phosphorus triiodide (42). Phosphorus tribromide, 270.8 g., is added during 60 min. to a suspension of 420 g. of sodium hydrogen carbonate in 200 ml. of water at 0-o°C. After 30 min. the mixture is treated with 330 ml. of IN hydrobromic acid. The slightly alkaline solution is evaporated under reduced pressure to 700 ml., filtered, and mixed with 900 ml. of 90% ethyl alcohol. The mixture is allowed to stand for 20 hr. in ice. The crystalline product is separated and dissolved in 150 ml. of water. The solution is treated with carbon and filtered. An equal volume of ethyl alcohol is added to the filtrate and the mixture is kept in ice for 4 hr. The precipitate, after being kept for 40 hr. on a porous plate at 0°C., yields 36 g. of a crude product. By treating the crude product with half its weight of water, 22 g. (air dried) of a product is crystallized. The crystals, 150 g. (6 preparations), are further crystallized twice from water to give 90 g. of a product. In order to re-... 

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. 

The hydrolysis of phosphorus tribromide or triiodide is used in the preparation of hydrogen bromide and hydrogen iodide respectively ... 

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. 

Tetraiododiphosphine, P2I4, which forms dark red crystals, p = 3.89 g/cc, is the most stable tet-rahalide. It can be prepared by reacting iodine with dry phosphine (4.229), by direct union of the elements in CS2 or from the triiodide and red phosphorus, or from HI and white P (4.15). 

A brief review has recounted the discovery and applications of phosphametallocenes. The synthesis and structure of l,l -diphospha[2]ferrocenophane have also appeared these derivatives are obtained starting with 1-phenyl-3,4-dimethylphosphole-2-carboxaldehyde in a six-step synthetic procedure. A general mini-review on phosphorus heterocycles also highlights the synthesis and use of a number of phosphaferrocenes. A phospha-ferrocenium compound has also been prepared as its triiodide [Gp Fe(Ci2H2oP)][l3]- Borane adducts of phosphaferrocenes have also been obtained simply by treating the appropriate phosphaferrocenes with boron tribromide. 

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