Titanium(III) chloride is the
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with the formula TiCl
3. At least four distinct species have this formula; additionally
hydrated
Drinking is the act of ingesting water or other liquids into the body through the mouth, proboscis, or elsewhere. Humans drink by swallowing, completed by peristalsis in the esophagus. The physiological processes of drinking vary widely among o ...
derivatives are known. TiCl
3 is one of the most common halides of titanium and is an important catalyst for the manufacture of
polyolefin
A polyolefin is a type of polymer with the general formula (CH2CHR)n where R is an alkyl group. They are usually derived from a small set of simple olefins (alkenes). Dominant in a commercial sense are polyethylene and polypropylene. More speciali ...
s.
Structure and bonding
In TiCl
3, each titanium atom has one ''d'' electron, rendering its derivatives
paramagnetic
Paramagnetism is a form of magnetism whereby some materials are weakly attracted by an externally applied magnetic field, and form internal, induced magnetic fields in the direction of the applied magnetic field. In contrast with this behavior, d ...
, that is, the substance is attracted into a magnetic field. Solutions of titanium(III) chloride are violet, which arises from
excitations of its
''d''-electron. The colour is not very intense since the transition is
forbidden by the
Laporte selection rule.
Four solid forms or
polymorphs of TiCl
3 are known. All feature titanium in an octahedral coordination sphere. These forms can be distinguished by
crystallography
Crystallography is the experimental science of determining the arrangement of atoms in crystalline solids. Crystallography is a fundamental subject in the fields of materials science and solid-state physics (condensed matter physics). The wor ...
as well as by their magnetic properties, which probes
exchange interaction
In chemistry and physics, the exchange interaction (with an exchange energy and exchange term) is a quantum mechanical effect that only occurs between identical particles. Despite sometimes being called an exchange force in an analogy to classical ...
s. β-TiCl
3 crystallizes as brown needles. Its structure consists of chains of TiCl
6 octahedra that share opposite faces such that the closest Ti–Ti contact is 2.91 Å. This short distance indicates strong metal–metal interactions (see figure in upper right). The three violet "layered" forms, named for their color and their tendency to flake, are called alpha (α), gamma (γ), and delta (δ). In α-TiCl
3, the chloride
anion
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s are
hexagonal close-packed
In geometry, close-packing of equal spheres is a dense arrangement of congruent spheres in an infinite, regular arrangement (or lattice). Carl Friedrich Gauss proved that the highest average density – that is, the greatest fraction of space occu ...
. In γ-TiCl
3, the chlorides anions are
cubic close-packed. Finally, disorder in shift successions, causes an intermediate between alpha and gamma structures, called the δ form. The TiCl
6 share edges in each form, with 3.60 Å being the shortest distance between the titanium cations. This large distance between titanium
cation
An ion () is an atom or molecule with a net electrical charge.
The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by convent ...
s precludes direct metal-metal bonding. In contrast, the trihalides of the heavier metals
hafnium
Hafnium is a chemical element with the symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri M ...
and
zirconium
Zirconium is a chemical element with the symbol Zr and atomic number 40. The name ''zirconium'' is taken from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian '' zargun'' (zircon; ''zar-gun'', ...
engage in metal-metal bonding. Direct Zr–Zr bonding is indicated in
zirconium(III) chloride
Zirconium(III) chloride is an inorganic compound with formula ZrCl3. It is a blue-black solid that is highly sensitive to air.
Preparation
The material was first claimed by Ruff and Wallstein who reduced zirconium tetrachloride with aluminium ...
. The difference between the Zr(III) and Ti(III) materials is attributed in part to the relative radii of these metal centers.
Synthesis and reactivity
TiCl
3 is produced usually by reduction of
titanium(IV) chloride
Titanium tetrachloride is the inorganic compound with the formula . It is an important intermediate in the production of titanium metal and the pigment titanium dioxide. is a volatile liquid. Upon contact with humid air, it forms thick clouds ...
. Older reduction methods used
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
:
:2 TiCl
4 + H
2 → 2 HCl + 2 TiCl
3
It can also be produced by the reaction of titanium metal and
hydrochloric acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid
Acid strength is the tendency of an acid, symbol ...
.
It is conveniently reduced with
aluminium
Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. I ...
and sold as a mixture with
aluminium trichloride
Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...
, TiCl
3·AlCl
3. This mixture can be separated to afford TiCl
3(
THF
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...
)
3. The complex adopts a meridional structure. This light-blue complex TiCl
3(THF)
3 forms when TiCl
3 is treated with
tetrahydrofuran
Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water-miscible organic liquid with low viscosity. It is ma ...
(THF).
:TiCl
3 + 3 C
4H
8O → TiCl
3(OC
4H
8)
3
An analogous dark green complex arises from complexation with
dimethylamine
Dimethylamine is an organic compound with the formula (CH3)2NH. This secondary amine is a colorless, flammable gas with an ammonia-like odor. Dimethylamine is commonly encountered commercially as a solution in water at concentrations up to aroun ...
. In a reaction where all ligands are exchanged, TiCl
3 is a precursor to the blue-colored complex
Ti(acac)3.
The more reduced
titanium(II) chloride
Titanium(II) chloride is the chemical compound with the formula TiCl2. The black solid has been studied only moderately, probably because of its high reactivity. Ti(II) is a strong reducing agent: it has a high affinity for oxygen and reacts irre ...
is prepared by the thermal
disproportionation
In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation states. More generally, the term can b ...
of TiCl
3 at 500 °C. The reaction is driven by the loss of volatile
TiCl4:
:2 TiCl
3 → TiCl
2 + TiCl
4
The ternary halides, such as A
3TiCl
6, have structures that depend on the cation (A
+) added.
Caesium chloride
Caesium chloride or cesium chloride is the inorganic compound with the formula Cs Cl. This colorless salt is an important source of caesium ions in a variety of niche applications. Its crystal structure forms a major structural type where each ...
treated with titanium(II) chloride and
hexachlorobenzene
Hexachlorobenzene, or perchlorobenzene, is an organochloride with the molecular formula C6Cl6. It is a fungicide formerly used as a seed treatment, especially on wheat to control the fungal disease bunt. It has been banned globally under the Sto ...
produces crystalline CsTi
2Cl
7. In these structures Ti
3+ exhibits octahedral coordination geometry.
Applications
TiCl
3 is the main
Ziegler–Natta catalyst A Ziegler–Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). Two broad classes of Ziegler–Natta catalysts are employed, distinguished by their solubility:
* He ...
, responsible for most industrial production of
polyethylene
Polyethylene or polythene (abbreviated PE; IUPAC name polyethene or poly(methylene)) is the most commonly produced plastic. It is a polymer, primarily used for packaging ( plastic bags, plastic films, geomembranes and containers including bo ...
. The catalytic activities depend strongly on the polymorph of the TiCl
3 (α vs. β vs. γ vs. δ) and the method of preparation.
Laboratory use
TiCl
3 is also a specialized
reagent
In chemistry, a reagent ( ) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs. The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a ...
in organic synthesis, useful for reductive coupling reactions, often in the presence of added reducing agents such as zinc. It reduces
oxime
In organic chemistry, an oxime is a organic compound belonging to the imines, with the general formula , where R is an organic side-chain and R’ may be hydrogen, forming an aldoxime, or another organic group, forming a ketoxime. O-substituted ...
s to
imine
In organic chemistry, an imine ( or ) is a functional group or organic compound containing a carbon–nitrogen double bond (). The nitrogen atom can be attached to a hydrogen or an organic group (R). The carbon atom has two additional single bo ...
s. Titanium trichloride can reduce nitrate to ammonium ion thereby allowing for the sequential analysis of nitrate and ammonia.
Slow deterioration occurs in air-exposed titanium trichloride, often resulting in erratic results, such as in reductive
coupling reaction A coupling reaction in organic chemistry is a general term for a variety of reactions where two fragments are joined together with the aid of a metal catalyst. In one important reaction type, a main group organometallic compound of the type R-M (R = ...
s.
Safety
TiCl
3 and most of its complexes are typically handled under
air-free conditions to prevent reactions with oxygen and moisture. Samples of TiCl
3 can be relatively air stable or
pyrophoric
A substance is pyrophoric (from grc-gre, πυροφόρος, , 'fire-bearing') if it ignites spontaneously in air at or below (for gases) or within 5 minutes after coming into contact with air (for liquids and solids). Examples are organolith ...
.
References
{{Chlorides
Titanium(III) compounds
Chlorides
Titanium halides
Reducing agents