Titanium tetrachloride

Description

Titanium ore was first discovered in 1791 in Cornish beach sands by an English clergyman, William Gregor. The actual identification of the oxide was made a few years later by a German chemist, M.H. Klaproth, who gave the metal constituent of this oxide the name titanium, after the Titans of Greek mythology. Pure metallic titanium was first produced in the early 1900s in 1910 by M.A. Hunter at Rensselaer Polytechnic Institute in cooperation with General Electric Company.
Titanium tetrachloride is an inorganic compound that is an important intermediate in the production of titanium metal and the pigment titanium dioxide. On contact with humid air, it forms opaque clouds of titanium dioxide (TiO2) and hydrogen chloride (HCl). Early attempts to isolate titanium metal from titanium tetrachloride were unsuccessful. The process was improved and commercialized by William Kroll of Luxembourg in the 1930s which involved the reduction of titanium tetrachloride with magnesium in an inert gas atmosphere. This process remains essentially unchanged today. The primary use of titanium tetrachloride is for titanium dioxide used in paints.
The production of titanium metal accounts for only 5% of annual titanium mineral consumption, with the remainder being used in the titanium pigment industry. Pigments are produced using either a sulfate process or a more environmentally acceptable carbochlorination process that converts TiO2 into TiCl4. The latter process also supplies the TiCl4 necessary for the production of titanium metal.

Chemical properties

Colorless liquid. Fumes strongly when exposed to moist air, forming a dense and persistent white cloud. Soluble in dilute hydrochloric acid; soluble in water with evolution of heat; concentrated aqueous solutions are stable and corrosive; dilute solutions precipitate insoluble basic chlorides.

Chemical properties

Description: Titanium tetrachloride is a noncombustible, colorless to light yellow liquid that fumes in air. Penetrating acrid odor.

The Uses of Titanium tetrachloride

Titanium tetrachloride is used as an intermediate in the manufacture of titanium metal, titanium dioxide, titanous chloride pigments, iridescent glass, and artificial pearls and as a starting material for a variety of organic and inorganic titanium compounds. It is also used as a dye, a polymerization catalyst, and as a catalyst in many organic syntheses because of it acidity and oxophilicity in many applications in the chemical industry. Titanium tetrachloride was formerly used as a smokeproducing screen with ammonia for the military; however, due to its extremely irritating and corrosive qualities in both liquid and smoke formulation, military applications are rarely used. The conversion of tetrachloride to titanium metal takes place by the reduction of chloride with magnesium which yields titanium metal and magnesium chloride and is referred to as the Kroll process after its inventor:
2 Mg ＋ TiCl4→2 MgCl2 ＋ Ti

The Uses of Titanium tetrachloride

Activates pyrrolidines for improved conversion, via a modified Bouveault reaction, to the corresponding α,α-dimethylamines.1

The Uses of Titanium tetrachloride

manufacture of titanium compounds, iridescent glass and artificial pearls. Formerly used with potassium bitartrate as a mordant in textile industry, and with dyewoods in dyeing leather; also as smoke-producing screen with ammonia.

The Uses of Titanium tetrachloride

Titanium (IV) tetrachloride (TiCl4) produces a dense white smoke-like vapor when exposed to moist air. It is used as smoke screens and for skywriting, as well in theatrical productions where fog or smoke is required for the scene.

Production Methods

TiCl4 is used in TiO2 production, the manufacture of artificial pearls and iridescent glass, and, by the military, to create smoke screens.

General Description

A colorless fuming liquid with a pungent odor. Corrosive to metals and tissue. Very toxic by inhalation.

Reactivity Profile

Titanium tetrachloride acts as an acid in aqueous solution. During the reduction of Titanium tetrachloride to titanium metal with potassium, an explosion occurred. The system had been heated to 90°C [Walter and Mandell 1967]. Addition directly to tetrahydrofuran caused a violent exothermic reaction [Inorg. Syn., 1982, 21, 135]. Ethylene can polymerize at low pressure if catalyzed by titanium halides. (Sundaram, K. M, M. M. Shreehan, E. F. Olszewski. thylene. Kirk-Othmer Encyclopedia of Chemical Technology. John Wiley & Sons, Inc. 2001.)

Hazard

Toxic by inhalation, strong irritant to skin and tissue.

Health Hazard

Titanium tetrachloride is a highly corrosive, acute irritant to the skin, eyes, mucous membranes and the respiratory tract. It is capable of causing death or permanent injury due to exposures encountered in normal use. Even short contact may lead to eye inflammation which may result in corneal opacities.

Fire Hazard

Material will react with water to produce hydrochloric acid. Titanium tetrachloride may ignite other combustible materials (e.g., wood, oil, etc.). Flammable, poisonous gases may accumulate in tanks and hopper cars. Runoff to sewer may create fire or explosion hazard. Reacts strongly with water to release hydrochloric acid and heat. Avoid water, moist air. Stable in concentrated aqueous solutions. Avoid contact with moisture; the chemical absorbs moisture from air and evolves dense white fumes.

Safety Profile

Poison by inhalation. A corrosive irritant to skin, eyes, and mucous membranes. When heated to decomposition it emits toxic fumes of Cl-. See also TITANIUM COMPOUNDS.

Potential Exposure

Used in the manufacture of titanium salts; mordant dye; titanium pigments; and used as a chemical intermediate for titanium metal; titanium dioxide; as an agent in smoke screens; polymerization catalyst; and iridescent agent in glass and pearl manufacturing.

Carcinogenicity

Rats exposed to 10 mg TiCl4/m³ for 6 h/day, 5 days/week, for 2 years developed rhinitis, tracheitis, hyperplasia, foamy dust cell accumulation, and alveolar bronchiolization. In addition, 5/150 animals developed squamous cell carcinoma, compared to 0/156 in the controls. Two of the squamous cell carcinomas were described as cystic keratinizing lesions, whose relevance to humans was questioned by the authors. However, the remaining three squamous cell tumors were described as microscopic, well-differentiated carcinomas. Therefore, TiCl4 may be regarded as potentially carcinogenic in the rat.

Environmental Fate

Titanium tetrachloride is a colorless to pale yellow liquid with a strong penetrating odor. If it comes in contact with water, it rapidly forms hydrochloric acid, as well as titanium compounds. Titanium tetrachloride is not found naturally in the environment and is made from minerals that contain titanium. Titanium tetrachloride is the most toxic of the titanium compounds and is highly corrosive and unstable and undergoes rapid hydrolysis through a vigorous exothermic reaction generating a large quantity of heat and hydrolysis products such as hydrochloric acid and other titanium compounds including titanium hydroxide, titanium oxychloride, and titanium dioxide. It may ignite other combustible materials (e.g., wood, oil, etc.) and produce toxic gases. Runoff to sewers may create fires or explosion hazards.
Titanium tetrachloride enters the environment primarily as air emissions from facilities that make or use it in these various chemical processes or as a result of accidental releases. Its chemical properties suggest that titanium tetrachloride partitions to the air underscoring the fact that the most likely route of human exposure to titanium tetrachloride hydrolysis or its intermediate products is via inhalation. The hydrochloric acid may break down or be carried in the air for some distance. Some of the titanium compounds may settle out to soil or in water as bottom sediments and remain for many years. Other titanium compounds, such as titanium dioxide, can also be found in the air. Consequently, environmental transport of titanium tetrachloride is negligible in soil and water; however, the atmospheric transport of the hydrolysis products may be significant. There is a paucity of data estimating the residence time for titanium tetrachloride in air or water; however, based on the compounds’ rapid hydrolysis, residence times are expected to be in the order of hours. In water, hydrochloric acid dissociates to the hydrogen and chloride ions, while titanium dioxide is insoluble in water and may settle out into the sediments. Titanium tetrachloride released to soils or sediments is expected to hydrolyze on contact with moisture in the soil and sediment. However, titanium dioxide is likely to remain in the soil or settle out to the sediment as it is an inert compound.
The chemical characteristics of titanium tetrachloride and its rapid hydrolysis in the presence of water suggest that there is little potential for bioaccumulation or biomagnification in aquatic or terrestrial organisms. It is not possible to determine if there is a potential for bioaccumulation of the compound in humans. Because of its chemical characteristics and rapid hydrolysis in the presence of water, however, it is also unlikely that it would bioaccumulate in the body although its final hydrolysis product may do so. Hence, titanium tetrachloride is not considered to be persistent, bioaccumulating, nor toxic.

Shipping

UN1838 Titanium tetrachloride, Hazard class: 6.1; Labels: 6.1-Poison Inhalation Hazard, 8-Corrosive material, Inhalation Hazard Zone B.

Purification Methods

Reflux it with mercury or a small amount of pure copper turnings to remove the last traces of colour [due to FeCl3 and VCl4], then distil it under N2 in an all-glass system, taking precautions to exclude moisture. Clabaugh et al. [J Res Nat Bur Stand 55 261 1955] removed organic material by adding aluminium chloride hexahydrate as a slurry with an equal amount of water (the slurry being ca one-fiftieth the weight of TiCl4), refluxed it for 2-6hours while bubbling in chlorine, the excess of which is subsequently removed by passing a stream of clean dry air. The TiCl4 is then distilled, refluxed with copper and again distilled, taking precautions to exclude moisture. Volatile impurities are then removed using a technique of freezing, pumping and melting. The titanium tetrachloride 2-tetrahydrofuran complex [Beilstein 17/1 V 33.] M 333.9, has m 126-128o and is easier to handle than TiCl4 [Abrahamson et al. Organometallics 3 1379 1984]. [Baxter & Fertig J Am Chem Soc 45 1228 1923, Baxter & Butler J Am Chem Soc 48 3117 1926.] HARMFUL VAPOURS.

Toxicity evaluation

It has been hypothesized that harmful effects of titanium tetrachloride are due to the vigorous reaction with water from perspiration on the skin, tears, and moisture in the air resulting in a severely exothermic reaction. The mechanism of injury is thought to be a combined thermal and acid burn process. Initially, there is a thermal burn, which exposes deeper tissue layers to hydrolysis products such as hydrochloric acid, furthering the severity of the effects.
The results of a mouse study showed that titanium tetrachloride was more toxic than hydrochloric acid. It is speculated that the more severe effects seen from exposure to titanium tetrachloride compared with hydrochloric acid is because hydrochloric acid is dissolved in the moisture of the nasopharynx and trachea remaining in this upper respiratory area and therefore is physically limited in the extent of lung penetration. However, in the case of exposure to titanium tetrachloride, the hydrolysis occurs in several steps. One of the hydrolysis products, titanium oxide hydrate, is a particulate that can adsorb the hydrochloric acid vapors that are also generated during hydrolysis and carry them into the deeper parts of the lungs and to the alveoli. However, titanium tetrachloride hydrolysis products such as titanium oxide hydrate can absorb some of the hydrochloric acid vapors that are also generated during hydrolysis and carry them past the upper respiratory spaces and into the deeper parts of the lungs. This mechanism of toxicity could potentially explain the second- and thirddegree burns observed after acute dermal exposure to titanium tetrachloride.

Incompatibilities

Violent reaction with water or steam, releasing heat and hydrogen chloride fumes. Contact with moist air releases hydrogen chloride. Attacks many metals in presence of moisture.