Titanium tetrachloride

Last updated
Titanium tetrachloride
Titanium-tetrachloride-3D-vdW.png
Sample of Titanium tetrachloride 01.jpg
Names
IUPAC name
Titanium(IV) chloride
Other names
Titanium tetrachloride
Tetrachlorotitanium
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.028.584
EC Number
  • 231-441-9
MeSH Titanium+tetrachloride
PubChem CID
RTECS number
  • XR1925000
UNII
UN number 1838
Properties
TiCl
4
Molar mass 189.679 g/mol
AppearanceColourless 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 in dichloromethane, [2] toluene, [3] pentane [4]
Vapor pressure 1.3 kPa (20 °C)
54.0·10−6 cm3/mol
1.61 (10.5 °C)
Viscosity 827 μPa s
Structure
Tetragonal
Tetrahedral
0 D
Thermochemistry
355 J·mol−1·K−1 [5]
−763 kJ·mol−1 [5]
Hazards [6]
Safety data sheet MSDS
GHS pictograms GHS-pictogram-acid.svg GHS-pictogram-skull.svg GHS-pictogram-exclam.svg
GHS Signal word Danger
H314, H317, H318, H330, H335, H370, H372
P280, P301+330+331, P304+340, P305+351+338, P308+310
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasReactivity code 2: Undergoes violent chemical change at elevated temperatures and pressures, reacts violently with water, or may form explosive mixtures with water. E.g. white phosphorusSpecial hazard W: Reacts with water in an unusual or dangerous manner. E.g. sodium, sulfuric acidTitanium tetrachloride
0
3
2
W
Related compounds
Other anions
Titanium(IV) bromide
Titanium(IV) fluoride
Titanium(IV) iodide
Other cations
Hafnium(IV) chloride
Zirconium(IV) chloride
Related compounds
Titanium(II) chloride
Titanium(III) chloride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Crystals of frozen titanium tetrachloride melting into the liquid Titanium tetrachloride phases.jpg
Crystals of frozen titanium tetrachloride melting into the liquid

Titanium tetrachloride is the inorganic compound with the formula TiCl4. It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. TiCl4 is a volatile liquid. Upon contact with humid air, it forms spectacular opaque clouds of titanium dioxide (TiO2) and hydrated hydrogen chloride. It is sometimes referred to as "tickle" or "tickle 4" due to the phonetic resemblance of its molecular formula (TiCl4) to the word. [7] [8]

Contents

Properties and structure

TiCl4 is a dense, colourless distillable 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 of TiCl4 weakly self-associate. Most metal chlorides are polymers, wherein the chloride atoms bridge between the metals. Its melting and boiling points are similar to those of CCl4.

Ti4+ has a "closed" electronic shell, with the same number of electrons as the inert gas argon. The tetrahedral structure for TiCl4 is consistent with its description as a d0 metal center (Ti4+) surrounded by four identical ligands. This configuration leads to highly symmetrical structures, hence the tetrahedral shape of the molecule. TiCl4 adopts similar structures to TiBr4 and TiI4; the three compounds share many similarities. TiCl4 and TiBr4 react to give mixed halides TiCl4−xBrx, where x = 0, 1, 2, 3, 4. Magnetic resonance measurements also indicate that halide exchange is also rapid between TiCl4 and VCl4. [9]

TiCl4 is soluble in toluene and chlorocarbons. Certain arenes form complexes of the type [(C6R6)TiCl3]+. TiCl4 reacts exothermically with donor solvents such as THF to give hexacoordinated adducts. [10] Bulkier ligands (L) give pentacoordinated adducts TiCl4L.

Production

TiCl4 is produced by the chloride process, which involves the reduction of titanium oxide ores, typically ilmenite (FeTiO3), with carbon under flowing chlorine at 900 °C. Impurities are removed by distillation.

2 FeTiO3 + 7 Cl2 + 6 C → 2 TiCl4 + 2 FeCl3 + 6 CO

The coproduction of FeCl3 is undesirable, which has motivated the development of alternative technologies. Instead of directly using ilmenite, "rutile slag" is used. This material, an impure form of TiO2, is derived from ilmenite by removal of iron, either using carbon reduction or extraction with sulfuric acid. Crude TiCl4 contains a variety of other volatile halides, including vanadyl chloride (VOCl3), silicon tetrachloride (SiCl4), and tin tetrachloride (SnCl4), which must be separated.

Applications

Production of titanium metal

The world's supply of titanium metal, about 250,000 tons per year, is made from TiCl4. The conversion involves the reduction of the tetrachloride with magnesium metal. This procedure is known as the Kroll process: [11]

2  Mg + TiCl4 → 2 MgCl2 + Ti

In the Hunter process, liquid sodium is the reducing agent instead of magnesium.

Production of titanium dioxide

Around 90% of the TiCl4 production is used to make the pigment titanium dioxide (TiO2). The conversion involves hydrolysis of TiCl4, a process that forms hydrogen chloride: [11]

TiCl4 + 2 H2O → TiO2 + 4 HCl

In some cases, TiCl4 is oxidised directly with oxygen:

TiCl4 + O2 → TiO2 + 2 Cl2

Smoke screens

It has been used to produce smoke screens since it produces a heavy, white smoke that has little tendency to rise. [12]

Chemical reactions

Titanium tetrachloride is a versatile reagent that forms diverse derivatives including those illustrated below.

TiCl4cmpds.png

The most noteworthy reaction of TiCl4 is its easy hydrolysis, signaled by the release of hydrogen chloride and the formation of titanium oxides and oxychlorides, as described above for the production of TiO2. Titanium tetrachloride has been used to create naval smokescreens. The hydrogen chloride immediately absorbs water to form an aerosol of hydrochloric acid that efficiently scatter light. In addition, the highly refractive titanium dioxide is also an efficient light scatterer. This smoke is however corrosive.

Alcohols react with TiCl4 to give the corresponding alkoxides with the formula [Ti(OR)4]n (R = alkyl, n = 1, 2, 4). As indicated by their formula, these alkoxides can adopt complex structures ranging from monomers to tetramers. Such compounds are useful in materials science as well as organic synthesis. A well known derivative is titanium isopropoxide, which is a monomer.

Organic amines react with TiCl4 to give complexes containing amido (R2N-containing) and imido (RN2−-containing) complexes. With ammonia, titanium nitride is formed. An illustrative reaction is the synthesis of tetrakis(dimethylamido)titanium Ti(NMe2)4, a yellow, benzene-soluble liquid: [13] This molecule is tetrahedral, with planar nitrogen centers. [14]

4 LiNMe2 + TiCl4 → 4 LiCl + Ti(NMe2)4

Complexes with simple ligands

TiCl4 is a Lewis acid as implicated by its tendency to hydrolyze. With the ether THF, TiCl4 reacts to give yellow crystals of TiCl4(THF)2. With chloride salts, TiCl4 reacts to form sequentially [Ti2Cl9], [Ti2Cl10]2− (see figure above), and [TiCl6]2−. [15] The reaction of chloride ions with TiCl4 depends on the counterion. NBu4Cl and TiCl4 gives the pentacoordinate complex NBu4TiCl5, whereas smaller NEt+
4
gives (NEt4)2Ti2Cl10. These reactions highlight the influence of electrostatics on the structures of compounds with highly ionic bonding.

Redox

Reduction of TiCl4 with aluminium results in one-electron reduction. The trichloride (TiCl3) and tetrachloride have contrasting properties: the trichloride is a solid, being a coordination polymer, and is paramagnetic. When the reduction is conducted in THF solution, the Ti(III) product converts to the light-blue adduct TiCl3(THF)3.

Organometallic chemistry

The organometallic chemistry of titanium typically starts from TiCl4. An important reaction involves sodium cyclopentadienyl to give titanocene dichloride, TiCl2(C5H5)2. This compound and many of its derivatives are precursors to Ziegler–Natta catalysts. Tebbe's reagent, useful in organic chemistry, is an aluminium-containing derivative of titanocene that arises from the reaction of titanocene dichloride with trimethylaluminium. It is used for the "olefination" reactions.

Arenes, such as C6(CH3)6 react to give the piano-stool complexes [Ti(C6R6)Cl3]+ (R = H, CH3; see figure above). [16] This reaction illustrates the high Lewis acidity of the TiCl+
3
entity, which is generated by abstraction of chloride from TiCl4 by AlCl3.

Reagent in organic synthesis

TiCl4 finds occasional use in organic synthesis, capitalizing on its Lewis acidity, its oxophilicity, and the electron-transfer properties of its reduced titanium halides [17] It is used in the Lewis acid catalysed aldol addition [18] Key to this application is the tendency of TiCl4 to activate aldehydes (RCHO) by formation of adducts such as (RCHO)TiCl4OC(H)R.

Toxicity and safety considerations

Hazards posed by titanium tetrachloride generally arise from the release of hydrogen chloride (HCl). TiCl4 is a strong Lewis acid, exothermically forming adducts with even weak bases such as THF and explosively with water, releasing HCl.

Related Research Articles

Silicon tetrachloride or tetrachlorosilane is the inorganic compound with the formula SiCl4. It is a colourless volatile liquid that fumes in air. It is used to produce high purity silicon and silica for commercial applications.

Lithium aluminium hydride, commonly abbreviated to LAH, is an inorganic compound with the chemical formula LiAlH4. It was discovered by Finholt, Bond and Schlesinger in 1947. This compound is used as a reducing agent in organic synthesis, especially for the reduction of esters, carboxylic acids, and amides. The solid is dangerously reactive toward water, releasing gaseous hydrogen (H2). Some related derivatives have been discussed for hydrogen storage.

Tin(IV) chloride, also known as tin tetrachloride or stannic chloride, is an inorganic compound with the formula SnCl4. It is a colorless hygroscopic liquid, which fumes on contact with air. It is used as a precursor to other tin compounds. It was first discovered by Andreas Libavius (1550–1616) and was known as spiritus fumans libavii.

Chromium(III) chloride chemical compound

Chromium(III) chloride (also called chromic chloride) describes any of several compounds of with the formula CrCl3 • xH2O, where x can be 0, 5, and 6. The anhydrous compound with the formula CrCl3 is a violet solid. The most common form of the trichloride is the dark green hexahydrate, CrCl3 • 6H2O. Chromium chlorides find use as catalysts and as precursors to dyes for wool.

Tantalum(V) chloride chemical compound

Tantalum(V) chloride, also known as tantalum pentachloride, is an inorganic compound with the formula TaCl5. It takes the form of a white powder and is commonly used as a starting material in tantalum chemistry. It readily hydrolyzes to form tantalum(V) oxychloride (TaOCl3) and eventually tantalum pentoxide (Ta2O5); this requires that it be synthesised and manipulated under anhydrous conditions, using air-free techniques.

Hafnium tetrachloride chemical compound

Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.

McMurry reaction

The McMurry reaction is an organic reaction in which two ketone or aldehyde groups are coupled to form an alkene using a titanium chloride compound such as titanium(III) chloride and a reducing agent. The reaction is named after its co-discoverer, John E. McMurry. The McMurry reaction originally involved the use of a mixture TiCl3 and LiAlH4, which produces the active reagent(s). Related species have been developed involving the combination of TiCl3 or TiCl4 with various other reducing agents, including potassium, zinc, and magnesium. This reaction is related to the Pinacol coupling reaction which also proceeds by reductive coupling of carbonyl compounds.

Boron trichloride is the inorganic compound with the formula BCl3. This colorless gas is a reagent in organic synthesis. It is highly reactive toward water.

Titanocene dichloride chemical compound

Titanocene dichloride is the organotitanium compound with the formula (η5-C5H5)2TiCl2, commonly abbreviated as Cp2TiCl2. This metallocene is a common reagent in organometallic and organic synthesis. It exists as a bright red solid that slowly hydrolyzes in air. It shows antitumour activity and was the first non-platinum complex to undergo clinical trials as a chemotherapy drug.

Zirconium(IV) chloride chemical compound

Zirconium(IV) chloride, also known as zirconium tetrachloride, (ZrCl4) is an inorganic compound frequently used as a precursor to other compounds of zirconium. This white high-melting solid hydrolyzes rapidly in humid air.

Titanium(III) chloride is the inorganic compound with the formula TiCl3. At least four distinct species have this formula; additionally hydrated derivatives are known. TiCl3 is one of the most common halides of titanium and is an important catalyst for the manufacture of polyolefins.

Vanadium tetrachloride is the inorganic compound with the formula VCl4. This bright red liquid serves as a useful reagent for the preparation of other vanadium compounds.

Molybdenum(V) chloride chemical compound

Molybdenum(V) chloride is the inorganic compound with the formula [MoCl5]2. This dark volatile solid is used in research to prepare other molybdenum compounds. It is moisture-sensitive and soluble in chlorinated solvents. Usually called molybdenum pentachloride, it is in fact a dimer with the formula Mo2Cl10.

Titanium tetrabromide chemical compound

Titanium tetrabromide is the chemical compound with the formula TiBr4. It is the most volatile transition metal bromide. The properties of TiBr4 are an average of TiCl4 and TiI4. Some key properties of these four-coordinated Ti(IV) species are their high Lewis acidity and their high solubility in nonpolar organic solvents. TiBr4 is diamagnetic, reflecting the d0 configuration of the metal centre.

Thorium(IV) chloride chemical compound

Thorium(IV) chloride (ThCl4) is an inorganic chemical compound. In addition to the anhydrous ThCl4, two hydrates have been reported: ThCl4(H2O)4 and ThCl4(H2O)8. These hygroscopic salts are water-soluble and white, at room temperature. Similar to other thorium complexes thorium(IV) chloride has a high melting point 770 °C (1,418 °F) and a boiling point of 921 °C (1,690 °F). Like all the other actinides, thorium is radioactive and has sometimes been used in the production of nuclear energy. Thorium(IV) chloride does not appear naturally but instead is derived from Thorite, Thorianite, or Monazite which are naturally occurring formations.

Organotitanium compound any metaloorganic compound having a carbon–titanium bond

Organotitanium compounds in organometallic chemistry contain carbon-to-titanium chemical bonds. Organotitanium chemistry is the science of organotitanium compounds describing their physical properties, synthesis and reactions. They are reagents in organic chemistry and are involved in major industrial processes.

Niobium(IV) chloride chemical compound

Niobium(IV) chloride, also known as niobium tetrachloride, is the chemical compound of formula NbCl4. This compound exists as dark violet crystals, is highly sensitive to air and moisture, and disproportiates into niobium(III) chloride and niobium(V) chloride when heated.

In organometallic chemistry, bent metallocenes are a subset of metallocenes. In bent metallocenes, the ring systems coordinated to the metal are not parallel, but are tilted at an angle. A common example of a bent metallocene is Cp2TiCl2. Several reagents and much research is based on bent metallocenes.

Molybdenum(III) chloride is the inorganic compound with the formula MoCl3.

Bis(cyclopentadienyl)titanium(III) chloride

Bis(cyclopentadienyl)titanium(III) chloride, also known as the Nugent–RajanBabu reagent, is the organotitanium compound which exists as a dimer with the formula [(C5H5)2TiCl]2. It is an air sensitive green solid. The complex finds specialized use in synthetic organic chemistry as a single electron reductant.

References

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General reading