 | |
 | |
| Names | |
|---|---|
| IUPAC name Titanium(IV) chloride | |
| Other names Titanium tetrachloride Tetrachlorotitanium | |
| Identifiers | |
3D model (JSmol) | |
| ChEBI | |
| ChemSpider |
|
| ECHA InfoCard | 100.028.584 |
| EC Number |
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| MeSH | Titanium+tetrachloride |
| RTECS number |
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| UNII | |
| UN number | 1838 |
| |
| |
| Properties | |
| TiCl4 | |
| Molar mass | 189.679 g/mol |
| Appearance | Colourless liquid |
| Odor | penetrating acid odor |
| Density | 1.726 g/cm3 |
| Melting point | −24.1 °C (−11.4 °F; 249.1 K) |
| Boiling point | 136.4 °C (277.5 °F; 409.5 K) |
| reacts (exothermic hydrolysis)[1] | |
| Solubility | soluble indichloromethane,[2]toluene,[3]pentane[4] |
| Vapor pressure | 1.3 kPa (20 °C) |
| −54.0·10−6 cm3/mol | |
Refractive index (nD) | 1.61 (10.5 °C) |
| Viscosity | 827 μPa s |
| Structure | |
| Tetragonal | |
| Tetrahedral | |
| 0 D | |
| Thermochemistry | |
Std molar entropy(S⦵298) | 355 J·mol−1·K−1[5] |
Std enthalpy of formation(ΔfH⦵298) | −763 kJ·mol−1[5] |
| Hazards[6] | |
| Occupational safety and health (OHS/OSH): | |
Main hazards | Toxic, corrosive, reacts with water to releaseHCl |
| GHS labelling: | |
   | |
| Danger | |
| H314,H317,H330,H335,H370,H372 | |
| P280,P301+P330+P331,P304+P340,P305+P351+P338,P308+P310 | |
| NFPA 704 (fire diamond) | |
| Safety data sheet (SDS) | MSDS |
| Related compounds | |
Otheranions | Titanium(IV) bromide Titanium(IV) fluoride Titanium(IV) iodide |
Othercations | Hafnium(IV) chloride Zirconium(IV) chloride |
Related compounds | Titanium(II) chloride Titanium(III) chloride |
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |
Titanium tetrachloride is theinorganic compound with theformulaTiCl4. It is an important intermediate in the production oftitanium metal and the pigmenttitanium dioxide.TiCl4 is avolatile liquid. Upon contact with humid air, it forms thick clouds oftitanium dioxide (TiO2) andhydrochloric acid, a reaction that was formerly exploited for use in smoke machines. It is sometimes referred to as "tickle" or "tickle 4", as a phonetic representation of the symbols of its molecular formula (TiCl4).[7][8]
TiCl4 is a dense, colourless liquid, although crude samples may be yellow or even red-brown. It is one of the rare transition metal halides that is a liquid at room temperature,VCl4 being another example. This property reflects the fact that molecules ofTiCl4 weakly self-associate. Most metal chlorides arepolymers, wherein the chloride atoms bridge between the metals. Itsmelting point is similar to that ofCCl4.[9][10]
Ti4+ has a "closed" electronic shell, with the same number of electrons as the noble gasargon. Thetetrahedral structure forTiCl4 is consistent with its description as a d0 metal center (Ti4+) surrounded by four identical ligands. This configuration leads to highlysymmetrical structures, hence the tetrahedral shape of the molecule.TiCl4 adopts similar structures toTiBr4 andTiI4; the three compounds share many similarities.TiCl4 andTiBr4 react to give mixed halidesTiCl4−xBrx, wherex = 0, 1, 2, 3, 4. Magnetic resonance measurements also indicate that halide exchange is also rapid betweenTiCl4 andVCl4.[11]
TiCl4 is soluble intoluene andchlorocarbons. Certainarenes form complexes of the type[(C6R6)TiCl3]+.[12]TiCl4 reactsexothermically with donorsolvents such asTHF to give hexacoordinatedadducts.[13] Bulkierligands (L) give pentacoordinatedadductsTiCl4L.
TiCl4 is produced by thechloride process, which involves thereduction of titanium oxide ores, typicallyilmenite (FeTiO3), withcarbon under flowingchlorine at 900 °C. Impurities are removed bydistillation.[10]
The coproduction ofFeCl3 is undesirable, which has motivated the development of alternative technologies. Instead of directly using ilmenite, "rutile slag" is used. This material, an impure form ofTiO2, is derived from ilmenite by removal of iron, either using carbon reduction or extraction withsulfuric acid. CrudeTiCl4 contains a variety of other volatile halides, includingvanadyl chloride (VOCl3),silicon tetrachloride (SiCl4), andtin tetrachloride (SnCl4), which must be separated.[10]
The world's supply of titanium metal, about 250,000 tons per year, is made fromTiCl4. The conversion involves the reduction of the tetrachloride withmagnesium metal. This procedure is known as theKroll process:[14]
In theHunter process, liquidsodium is thereducing agent instead of magnesium.[15]
Around 90% of theTiCl4 production is used to make the pigmenttitanium dioxide (TiO2). The conversion involveshydrolysis ofTiCl4, a process that formshydrogen chloride:[14]
In some cases,TiCl4 is oxidised directly withoxygen:
It has been used to producesmoke screens since it produces a heavy, white smoke that has little tendency to rise. "Tickle" was the standard means of producing on-set smoke effects for motion pictures, before being phased out in the 1980s due to concerns abouthydrated HCl's effects on the respiratory system.[citation needed]
Titanium tetrachloride is a versatile reagent that forms diverse derivatives including those illustrated below.[16]
A characteristic reaction ofTiCl4 is its easyhydrolysis, signaled by the release ofHCl vapors andtitanium oxides andoxychlorides. Titanium tetrachloride has been used to create navalsmokescreens, as the hydrochloric acid aerosol and titanium dioxide that is formed scatter light very efficiently. This smoke is corrosive, however.[10]
Alcohols react withTiCl4 to give alkoxides with the formula[Ti(OR)4]n (R =alkyl,n = 1, 2, 4). As indicated by their formula, thesealkoxides can adopt complex structures ranging from monomers to tetramers. Such compounds are useful inmaterials science as well asorganic synthesis. A well known derivative istitanium isopropoxide, which is a monomer.Titanium bis(acetylacetonate)dichloride results from treatment of titanium tetrachloride with excessacetylacetone:[17]
Organicamines react withTiCl4 to give complexes containing amido (R2N−-containing) and imido (RN2−-containing) complexes. With ammonia,titanium nitride is formed. An illustrative reaction is the synthesis oftetrakis(dimethylamido)titaniumTi(N(CH3)2)4, a yellow, benzene-soluble liquid:[18] This molecule is tetrahedral, with planar nitrogen centers.[19]
TiCl4 is aLewis acid as implicated by its tendency tohydrolyze. With theetherTHF,TiCl4 reacts to give yellow crystals ofTiCl4(THF)2. With chloride salts,TiCl4 reacts to form sequentially[Ti2Cl9]−,[Ti2Cl10]2− (see figure above), and[TiCl6]2−.[20] The reaction of chloride ions withTiCl4 depends on the counterion.[N(CH2CH2CH2CH3)4]Cl andTiCl4 gives the pentacoordinate complex[N(CH2CH2CH2CH3)4][TiCl5], whereas smaller[N(CH2CH3)4]+ gives[N(CH2CH3)4]2[Ti2Cl10]. These reactions highlight the influence of electrostatics on the structures of compounds with highly ionic bonding.
Reduction ofTiCl4 withaluminium results in one-electron reduction. The trichloride (TiCl3) and tetrachloride have contrasting properties: the trichloride is a colored solid, being acoordination polymer, and isparamagnetic. When the reduction is conducted inTHF solution, the Ti(III) product converts to the light-blue adductTiCl3(THF)3.
Theorganometallic chemistry of titanium typically starts fromTiCl4. An important reaction involves sodiumcyclopentadienyl to givetitanocene dichloride,TiCl2(C5H5)2. This compound and many of its derivatives are precursors toZiegler–Natta catalysts.Tebbe's reagent, useful in organic chemistry, is an aluminium-containing derivative of titanocene that arises from the reaction of titanocene dichloride withtrimethylaluminium. It is used for the "olefination" reactions.[16]
Arenes, such asC6(CH3)6 react to give thepiano-stool complexes[Ti(C6R6)Cl3]+ (R = H,CH3; see figure above). This reaction illustrates the high Lewis acidity of theTiCl+3 entity, which is generated by abstraction ofchloride fromTiCl4 byAlCl3.[12]
TiCl4 finds occasional use inorganic synthesis, capitalizing on itsLewis acidity, itsoxophilicity, and the electron-transfer properties of its reduced titanium halides. It is used in theLewis acid catalysedaldol addition[21] Key to this application is the tendency ofTiCl4 to activatealdehydes (RCHO) by formation ofadducts such as(RCHO)TiCl4OC(H)R.[22]
Hazards posed by titanium tetrachloride generally arise from its reaction with water that releaseshydrochloric acid, which is severely corrosive itself and whose vapors are also extremely irritating.TiCl4 is a strongLewis acid, which exothermically forms adducts with even weak bases such asTHF and water.
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