Titanium tetraiodide

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). 

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). 

Iodine and antimony powder react so violently as to cause ignition or explosion of the bulk of the mixture. A mixture of potassium and iodine explodes weakly on impact, while potassium ignites in contact with molten iodine [1], Interaction of molten iodine with titanium above 113°C under vacuum to form titanium tetraiodide is highly exothermic and sparks are produced. The preparative technique described permits the progressive reaction of 0.5 g portions of the titanium powder charged (7.2 g) to minimise hazard [2],... 

Silver difluoride, 0014 Silver fluoride, 0013 Sodium chloride, 4036 Sodium iodide, 4623 Tantalum pentachloride, 4185 Tellurium tetrabromide, 0296 Thallium, 4922 Tin(II) chloride, 4116 Tin(IV) chloride, 4174 Tin(II) fluoride, 4331 Titanium(II) chloride, 4117 Titanium dibromide, 0284 Titanium diiodide, 4630 Titanium tetrachloride, 4176 Titanium tetraiodide, 4638 Titanium trichloride, 4158... 

Very highly pure titanium metal can be prepared in small amounts by decomposition of pure titanium tetraiodide, (Tih) vapor on a hot wire under low pressure (Van Arkel-de Boer method). 

Et2AlCl Catalyst. Under the same conditions as above 20 grams of PVC and 2 grams of cis-1,4-polybutadiene, prepared with an alkyl-aluminum-titanium tetraiodide catalyst system (95% cis-1,4 content, intrinsic viscosity at 25°C in benzene 2.2) in 200 ml chlorobenzene were allowed to react in the presence of 2 mmoles of Et2AlCl at 5°-10°C for 60 minutes. The reaction product was isolated by precipitation in methanol and dried to yield 22.0 grams of modified poly (vinyl chloride). Hexane extraction under reflux for 24 hours removed 8% of hexane-soluble material. 

See other HALOPHOSPHINES, IODINE COMPOUNDS, NON-METAL HALIDES 4633. Titanium tetraiodide... 

If nitrogen is used, the ideal deposition temperature is 1000°C. The deposition temperature is lower for the ammonia reaction (575 700°C). Plasma processing can be used to reduce the processing temperature to 500°C . Thermal laser CVD has also been used to deposit TiN at reduced temperature . In an alternate approach, titanium tetraiodide is the precursor (with no plasma) at a deposition temperature under 450°CT... 

Neutral tetrahalides also give rise to intense resonance Raman spectra, that of titanium tetraiodide being particularly simple and extended (Fig. 12). Other tetrahalides are expected likewise to yield good resonance Raman spectra, especially when further uv excitation lines become available. 

Fig. 12. Resonance Raman spectrum of solid titanium tetraiodide = 514.5 nm, power 1 W,...

The major end-use of iodine is in catalysis (e.g., the Monsanto process for producing acetic acid). Titanium tetraiodide and aluminum iodide are also significant in the dehydrogenation of butane and butene to butadiene, and in the preparation of stereoregular polymers. The second major end-use of iodine is as a stabilizer in the manufacture of nylon, for converting resins, tall oil and other wood products to more stable forms, while the third major use is as additives for animal and human food (iodization of salt and mineral mixtures). 

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