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Environmental fate & pathways

Hydrolysis

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Description of key information

Risk characterisation must, for all end points, address primarily the hydrolysis products.

Key value for chemical safety assessment

Half-life for hydrolysis:
0.1 min
at the temperature of:
4 °C

Additional information

The hydrolysis study does not need to be conducted as substance produces insoluble oxide after rapid hydrolysis. Waterborne titanium tetrachloride hydrolyses rapidly with an assumed half-life of below 0.1 min (Fisk et al 2010). Therefore measurement of the hydrolysis rate is not technically feasible. The hazard assessment bases accordingly on the hydrolysis products.

Titanium tetrachloride hydrolyses to in two steps to hydrogen chloride (CAS 7647-01-0) and titanium oxychloride (CAS 92344-13-3), which hydrolyzes to titanium dioxide (CAS 13463-67-7) and again hydrogen chloride. Intermediate formation of hydroxides, e.g. titanium dihydroxide oxide (CAS 12026-28-7) and/or titanium hydroxide (CAS 12651-23-9 or 20338-08-3) is probable. The titanium dioxide formed is amorphous or has weak crystallinity but corresponds finally to the naturally occurring mineral rutile albeit in micro-disperse form. It is considered stable under environmental conditions (Fisk et al 2010, Kim et al 1999).

According to the OECD SIDS report on hydrogen chloride (SIAR 2002) hydrogen chloride gets readily dissociated in contact with water into chlorides (CAS 16887-00-6) and via the proton (CAS 12586-59-3) into hydronium ions (CAS 13968-08-6).

Rigo et al (1998) investigated the kinetics of titanium tetrachloride in a moist atmosphere using tailor made laboratory reactors. In the presence of any air humidity rapid hydrolysis forms the volatile compound Ti(OH)2Cl2 instantaneous together with 2 mol hydrogen chloride. The former forms a very fine dust, which easily evolves to aerosols and hydrolyses further to titanium hydroxide (Rigo et al 1998, Watson & Kibler 1931). The half life of the second reaction step is ca. 6 h (Rigo et al 1998). Eventually the above mentioned amorphous complexes and finally the titanium dioxide particle sizes ranges about 400 to 700 nm (Watson & Kibler 1931).

  • Rigo M, Canu P, Angelin L, Della Valle G (1998) Kinetics of TiCl4 Hydrolysis in a Moist Atmosphere, Industrial & Engineering Chemistry Research 37(4):1189-95
  • Watson PD, Kibler AL (1931) The Relation between Obscuring Power and Particle, Number and Size of Screening Smoke. DOI: 10.1021/j150322a013 J. Phys. Chem. 35(4):1074–90