Tetraiodide

Diphosphorus tetraiodide is formed exothermically from the elements mixed Inthe stoichiometric ratio. The reaction can be moderated with CS3, which also serves as a solvent  

red prisms. M.p. 125.5°C Decomposes with water to H3PO3, PH and HI. 

Phosphorus (III) iodide can be prepared either from red or white P, dissolved in CSg, by reaction with a solution of Ig in CSg  

As Germann and Traxler have established, very carefully purified CSg must be used. Impure CSg, containing S, causes the formation of sulfurated PI3, the presence of which lowers the melting point. 

The required amoimt of Ig is dissolved in CSg, and excess red P is added. After the disappearance of free Ig, the dark-red, opaque solution is filtered from unreacted P and the CSg is distilled off on a sand bath until crystals appear. The solution is then allowed to cool, the supernatant liquid is decanted, and the remaining crystals are gently warmed. 

Submitted bt R. E. McAbthur and J. H. Simons Checked bt Karl M. BECKf 

Carbon tetraiodide has been prepared by the interaction of carbon tetrachloride and various metallic iodides, such as aluminum iodide, boron iodide, calcium iodide, and lithium iodide. The procedure here described makes use of readily available materials and involves the reaction of carbon tetrachloride with ethyl iodide in the presence of aluminum chloride.  

A 200-ml. flask is fitted with a cork stopper contaming a calcium chloride drying tube to permit the evolution of ethyl chloride but to prevent the influx of moisture from 

Immediately on adding the catalyst the reaction mixture turns red and ebullition and effervescence begin. Red crystals form gradually on the bottom of the flask. Occasional swirling helps to keep the reactants well mixed. After about 45 minutes a heavy deposit of red crystals will have formed very little liquid will be present. The crystals are collected in a Buchner funnel using mild suction, and are washed with three 25-ml. portions of ice-cold water to remove the aluminum chloride and then with three 25-ml. portions of ethyl alcohol to remove unreacted carbon tetrachloride and ethyl iodide. Washing with water causes the crystals to darken, but subsequent treatment with the alcohol restores the product to its natural bright red color. 

The crystals are dried in a vacuum dedccator containing sulfuric acid. The 3deld is about 12 g. (60 per cent). 

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It was originally separated from zirconium by repeated recrystallization of the double ammonium or potassium fluorides by von Hevesey and Jantzen. Metallic hafnium was first prepared by van Arkel and deBoer by passing the vapor of the tetraiodide over a heated tungsten filament. Almost all hafnium metal now produced is made by reducing the tetrachloride with magnesium or with sodium (Kroll Process). 

Hafnium tetrabromide [13777-22-5], HfBr, is very similar to the tetrachloride in both its physical and chemical properties. Hafnium tetraiodide [13777-23-6], Hfl, is produced by reaction of iodine with hafnium metal at 300°C or higher. At temperatures above 1200°C, the iodide dissociates to hafnium metal and iodine. These two reactions are the basis for the iodide-bar refining process. Hafnium iodide is reported to have three stable crystalline forms at 263—405°C (60). 

Iodides. Iodides range from the completely ionic such as potassium iodide [7681-11-0] KI, to the covalent such as titanium tetraiodide [7720-83-4J, Til. Commercially, iodides are the most important class of iodine compounds. In general, these are very soluble in water and some are hygroscopic. However, some iodides such as the cuprous, lead, silver and mercurous, are insoluble. 

Catalysts. Iodine and its compounds ate very active catalysts for many reactions (133). The principal use is in the production of synthetic mbber via Ziegler-Natta catalysts systems. Also, iodine and certain iodides, eg, titanium tetraiodide [7720-83-4], are employed for producing stereospecific polymers, such as polybutadiene mbber (134) about 75% of the iodine consumed in catalysts is assumed to be used for polybutadiene and polyisoprene polymeri2a tion (66) (see RUBBER CHEMICALS). Hydrogen iodide is used as a catalyst in the manufacture of acetic acid from methanol (66). A 99% yield as acetic acid has been reported. In the heat stabiH2ation of nylon suitable for tire cordage, iodine is used in a system involving copper acetate or borate, and potassium iodide (66) (see Tire cords). 

Phosphine generated by the above procedures is usually contaminated to varying degrees with diphosphine, which renders it spontaneously flammable. Pure phosphine can be produced by hydrolysis of phosphonium iodide [12125-09-6] PH I, which can be made by the action of water on a mixture of phosphoms and diphosphoms tetraiodide [13455-00-0] (71). 

Tellurium Tetraiodide. Tellurium tertaiodide [7790-48-9] Tel, forms gray-black volatile crystals which above 100°C decompose into the elements. They melt at 280°C in a sealed tube. 

Titanium diiodide may be prepared by direct combination of the elements, the reaction mixture being heated to 440°C to remove the tri- and tetraiodides (145). It can also be made by either reaction of soHd potassium iodide with titanium tetrachloride or reduction of Til with silver or mercury. 

Titanium Triiodlde. Titanium triiodide is a violet crystalline soHd having a hexagonal unit cell (146). The crystals oxidize rapidly in air but are stable under vacuum up to 300°C above that temperature, disproportionation to the diiodide and tetraiodide begins (147). 

Titanium triiodide can be made by direct combination of the elements or by reducing the tetraiodide with aluminum at 280°C in a sealed tube. Til reacts with nitrogen, oxygen, and sulfur donor ligands to give the corresponding adducts (148). 

Titanium Tetraiodide. Titanium tetraiodide [7720-83 ] forms reddish-brown crystals, cubic at room temperature, having reported lattice parameter of either 1200 (149) or 1221 (150) pm. Til melts at 150°C, boils at 377°C, and has a density of 440(0) kg/m. It forms adducts with a number of donor molecules and undergoes substitution reactions (151). It also hydrolyzes in water and is readily soluble in nonpolar organic solvents. 

Titanium tetraiodide can be prepared by direct combination of the elements at 150—200°C it can be made by reaction of gaseous hydrogen iodide with a solution of titanium tetrachloride in a suitable solvent and it can be purified by vacuum sublimation at 200°C. In the van Arkel method for the preparation of pure titanium metal, the sublimed tetraiodide is decomposed on a tungsten or titanium filament held at ca 1300°C (152). There are frequent hterature references to its use as a catalyst, eg, for the production of ethylene glycol from acetylene (153). 

Iodides. Tungsten tetraiodide [14055-84-6] WI, is a black powder that is decomposed by air. It is prepared by the action of concentrated hydriodic acid on tungsten hexachlotide at 100°C. 

High purity zirconium was first produced by van Arkel and de Boer in 1925. They vaporized zirconium tetraiodide [13986-26-0] into a bulb containing a hot tungsten filament which caused the tetraiodide to dissociate, depositing zirconium on the filament. 

Zirconium tetraiodide [13986-26-0], Zrl, is prepared directly from the elements, by the reaction of iodine on zirconium carbide, or by halogen exchange with aluminum triiodide. The reaction of iodine with zirconium oxide and carbon does not proceed. The physical properties are given in Table 7. 

Zirconium tetraiodide is the least thermally stable zirconium tetrahaUde. At 1400°C, it disproportionates to Zr metal and iodine vapor. This behavior is utilized in the van Arkel-de Boer process to refine zirconium. As with the tetrachloride and tetrabromide, the tetraiodide forms additional adducts with gaseous ammonia which, upon heating, decompose through several steps ending with zirconium nitride. 

When treated with aluminum bromide at 100°C, carbon tetrachloride is converted to carbon tetrabromide [558-13-4], reaction with calcium iodide, Cal2, at 75°C gives carbon tetraiodide [507-25-5]. With concentrated hydroiodic acid at 130°C, iodoform [75-47-8], CHI, is produced. Carbon tetrachloride is unaffected by gaseous fluorine at ordinary temperatures. Replacement of its chlorine by fluorine is brought about by reaction with hydrogen fluoride at a... 

To return to die problem of die vaporization of die tantalum silicides, which could be transported as the tetraiodide of each element, but not as the elementary species. From these data it can be concluded that whatever die starting point in the composition range, the composition of the surface phase will tend towards Tag Sis, which is die most nearly congruently vaporizing composition. 

Tetrajod-. tetraiodo- tetraiodide of. -kohlen-stoff, m. carbon tetraiodide. 

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