Titanium tetrachloride

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Titanium tetrachloride
Spacefill model of titanium tetrachloride
Spacefill model of titanium tetrachloride
Names
IUPAC name
Titanium(IV) chloride
Other names
Titanium tetrachloride
Tetrachlorotitanium
Identifiers
3D model (
JSmol
)
ChEBI
ChemSpider
ECHA InfoCard
 100.028.584 Edit this at Wikidata
EC Number
  • 231-441-9
MeSH Titanium+tetrachloride
RTECS number
  • XR1925000
UNII
UN number 1838
  • InChI=1S/4ClH.Ti/h4*1H;/q;;;;+4/p-4 checkY
    Key: XJDNKRIXUMDJCW-UHFFFAOYSA-J checkY
  • InChI=1/4ClH.Ti/h4*1H;/q;;;;+4/p-4/rCl4Ti/c1-5(2,3)4
    Key: XJDNKRIXUMDJCW-FOGBWSKZAG
SMILES
  • Cl[Ti](Cl)(Cl)Cl
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 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]
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 release HCl
GHS labelling:
GHS05: CorrosiveGHS06: ToxicGHS07: Exclamation mark
Danger
H314, H317, H330, H335, H370, H372
P280, P301+P330+P331, P304+P340, P305+P351+P338, P308+P310
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 0: Will not burn. E.g. waterInstability 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 acid
3
0
2
W
Safety data sheet (SDS) MSDS
Related compounds
Other anions
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).
checkY verify (what is checkY☒N ?)
clear crystals under a clear liquid at the bottom of a glass flask
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 thick clouds of titanium dioxide (TiO2) and hydrochloric 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]

Properties and structure

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 of TiCl4 weakly self-associate. Most metal chlorides are polymers, wherein the chloride atoms bridge between the metals. Its melting point is similar to that of CCl4.[9][10]

Ti4+ has a "closed" electronic shell, with the same number of electrons as the noble gas

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.[11]

TiCl4 is soluble in

THF to give hexacoordinated adducts.[13] 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.[10]

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

The coproduction of

tin tetrachloride (SnCl4), which must be separated.[10]

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:[14]

2 Mg + TiCl4 → 2 MgCl2 + Ti

In the Hunter process, liquid sodium is the reducing agent instead of magnesium.[15]

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:[14]

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. "Tickle" was the standard means of producing on-set smoke effects for motion pictures, before being phased out in the 1980s due to concerns about hydrated HCl's effects on the respiratory system.[16]

Chemical reactions

Titanium tetrachloride is a versatile reagent that forms diverse derivatives including those illustrated below.[17]

A characteristic reaction of TiCl4 is its easy

smokescreens, as the hydrochloric acid aerosol and titanium dioxide that is formed scatter light very efficiently. This smoke is corrosive, however.[10]

Alcohols react with TiCl4 to give 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. Titanium bis(acetylacetonate)dichloride results from treatment of titanium tetrachloride with excess acetylacetone:[18]

TiCl4 + 2 Hacac → Ti(acac)2Cl2 + 2 HCl

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(N(CH3)2)4, a yellow, benzene-soluble liquid:[19] This molecule is tetrahedral, with planar nitrogen centers.[20]

4 LiN(CH3)2 + TiCl4 → 4 LiCl + Ti(N(CH3)2)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−.[21]
The reaction of chloride ions with TiCl4 depends on the counterion. [N(CH2CH2CH2CH3)4]Cl and TiCl4 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.

Redox

Reduction of TiCl4 with

paramagnetic. When the reduction is conducted in THF
solution, the Ti(III) product converts to the light-blue adduct TiCl3(THF)3.

Organometallic chemistry

Main article:
Organotitanium compound

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.[17]

AlCl3.[12]

Reagent in organic synthesis

TiCl4 finds occasional use in

aldol addition[22] Key to this application is the tendency of TiCl4 to activate aldehydes (RCHO) by formation of adducts such as (RCHO)TiCl4OC(H)R.[23]

Toxicity and safety considerations

Hazards posed by titanium tetrachloride generally arise from its reaction with water that releases

THF
and water.

References

  1. S2CID 93971747
    .
  2. ^ "titanium(IV) chloride, 1M soln. in dichloromethane". Alfa Aesar. Retrieved 7 March 2018.
  3. ^ "Titanium(IV) chloride solution 1.0 M in toluene". Sigma-Aldrich. Retrieved 7 March 2018.
  4. ^ Butts, Edward H De. "patent US3021349A".
  5. ^
    ISBN 978-0-618-94690-7
    .
  6. ^ "Classifications - CL Inventory". echa.europa.eu.
  7. ^ [1] Archived 2013-02-17 at the Wayback Machine American Chemistry Council – "Titanium Tetrachloride: Stepping Stone to Amazing Technology"
  8. ^ "Archived copy". Archived from the original on 2014-03-19. Retrieved 2013-04-10.{{cite web}}: CS1 maint: archived copy as title (link) Iowa State University – "Chemistry Material Safety Data Sheets"
  9. ^ Earnshaw, A.; Greenwood, N. (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann.
  10. ^
    ISBN 978-3-527-30673-2
    .
  11. doi:10.1021/ja983339i
    .
  12. ^
    doi:10.1016/0022-328X(96)06194-3
    .
  13. ISBN 978-0-470-13252-4
    .
  14. ^
    ISBN 978-3-527-30673-2
    .
  15. ISBN 978-0-19-965145-0
    .
  16. ^ The Royal Navy at War (DVD). London: Imperial War Museum. 2005.
  17. ^
    ISBN 0-387-15784-0
  18. ISBN 978-0-470-13250-0. {{cite book}}: |journal= ignored (help
    )
  19. doi:10.1039/JR9600003857
    .
  20. doi:10.1016/j.poly.2005.10.019
    .
  21. doi:10.1039/DT9750001402
    .
  22. ^ Mariappan Periasamy (2002): "New synthetic methods using the TiCl4-NR3 reagent system", Arkivoc, p. 151-166.
  23. ^ Gundersen, L.-L.; Rise, F.; Undheim, K. (2004). "Titanium(IV) chloride". In Paquette, L. (ed.). Encyclopedia of Reagents for Organic Synthesis. New York, NY: J. Wiley & Sons.

General reading
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