Dichloride titanium oxide

Endpoint summary

Description of key information

Titanium oxychloride is an unstable chemical compound which results from the hydrolysis of titanium tetrachloride. The corrosiveness of both, parent chemical titanium tetrachloride and target chemical titanium oxychloride, is being determined by HCl getting formed during this chemical process and therefore being present in the chemical equilibrium. For these reasons it is proposed to generally classify titanium oxychloride as skin corrosive. Titanium oxychloride further shall be classified as respiratory irritant if c(HCl) > 10%.

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (corrosive)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (irritating)

Additional information

Titanium oxychloride is an unstable chemical compound which results from the hydrolysis of titanium tetrachloride.

1. step: TiCl4 + H2O ↔ TiOCl2 + 2 HCl

2. step: TiOCl2 + H2O ↔ TiO2 + 2 HCl

Summary reaction: TiCl4 + 2 H2O ↔ TiO2 + 4 HCl

In water this reaction takes place immediately. Therefore, under physiologically and environmentally relevant conditions titanium tetrachloride hydrolyses rapidly according to above stated two steps to hydrogen chloride and titanium oxychloride, which hydrolyses to titanium dioxide and again hydrogen chloride.

Skin corrosion:

Titanium oxychloride only can get stabilised in the presence of hydrogen chloride and cannot be separated from the aqueous solution. In addition to hydrogen chloride present in solution as stabiliser, hydrogen chloride is also produced as a product of hydrolysis. Hydrogen chloride is labelled as C; R34 under Directive 67/548/EEC and ‘Skin corr. 1B Causes severe skin burns and eye damage’ under 1272/2008. Therefore, titanium oxychloride is corrosive on the basis of pH and classification of hydrogen chloride. This conclusion is supported by read across from the titanium tetrachloride study [Foulger 1949]. Read-across from parent compound titanium tetrachloride to target compound titanium oxychloride is considered justified as titanium oxychloride is the product of partial hydrolysis of titanium tetrachloride. In contact with water the intermediate titanium oxychloride eventually will react to final hydrolysis products titanium dioxide and hydrogen chloride.

Respiratory irritation:

The reactions shown above indicate that titanium oxychloride exists in a chemical equilibrium with hydrochloric acid. As hydrochloric acid is noted to have a relatively high vapour pressure, and as the substance has a harmonised classification according to CLP Annex VI as respiratory irritant in the relevant concentration range, it is proposed to follow for target compound titanium oxychloride the harmonised classification as given for hydrochloric acid concerning respiratory irritation properties.

Note titanium oxychloride only is stabilised in aqueous medium in its hydrated form in equilibrium with hydrochloric acid, thus no atmospheric emissions occur. To a certain extent the evaporation of hydrochloric acid still might be observed.

Effects on skin irritation/corrosion: corrosive

Effects on eye irritation: corrosive

Effects on respiratory irritation: irritating

Justification for classification or non-classification

General considerations:

Based on the elaborations above, respiratory irritation and skin corrosiveness properties of target substance titanium oxychloride depend (1) from the concentration of hydrochloric acid always present in the chemical equilibrium in order to stabilise the target substance, and (2) from the fact that HCl furthermore is resulting in bimolar quantities from the hydrolysis reaction of the target chemical titanium oxychloride itself.

Discussions on skin corrosion classification:

According to the harmonised classification and labelling as given for hydrochloric acid, Annex VI of Regulation 1272/2008 (017 -002 -01 -X), hydrochloric acid is being classified as Skin Corr. 1B H314 if c(HCl) ≥ 25%, thus this classification automatically applies to titanium oxychloride containing aqueous solutions if c(HCl) ≥ 25%. In case 10%≤ c(HCl) <25%, Skin irrit. 2 H315 and Eye irrit. 2 H319 would apply, and in case c(HCl) < 10% even no classification at all would apply. However for aqueous solutions containing titanium oxychloride it is proposed to always classify as Skin Corr. 1B, as HCl is resulting in bimolar quantities fom the hydrolysis reaction of the target chemical titanium oxychloride itself.

Discussions on respiratory irritation classification:

According to the harmonised classification and labelling as given for hydrochloric acid, Annex VI of Regulation 1272/2008 (017 -002 -01 -X), hydrochloric acid is being classified as STOT SE 3 H335, Resp. Irrit. for c(HCl) ≥ 10%. In this case it is proposed to stick also for titanium oxychloride to the harmonised classification for hydrochloric acid, as (1) target substance titanium oxychloride only can get stabilised in aqueous medium in its hydrated form in chemical equilibrium with hydrochloric acid, and thus cannot evaporate to the atmosphere and (2) hydrochloric acid still might be evaporating from the system to a certain extent (e.g. considering the vapour pressure).

Proposed classification and labelling for titanium oxychloride acc. to CLP Regulation 1272/2008:

Hazard class and code in case c(HCl) ≥ 10%:

Skin Corr. 1B, H314

Resp. Irrit. STOT SE 3, H335

Labelling: GHS05, GHS07, Danger

Hazard class and code in case c(HCl) < 10%:

Skin Corr. 1B, H314

Labelling: GHS05, Danger

Proposed classification and labelling for titanium oxychloride according to Directive 67/548/EEC:

Hazard class and code in case c(HCl) ≥ 10%:

C;R34

Xi;R37

Labelling: C and R34 -37

Hazard class and code in case c(HCl) < 10%:

C; R34

Labelling: C and R34

Hydrolysis of titanium tetrachloride via titanium oxychloride produces hydrochloric acid, which is sufficient to justify the classification of titanium oxychloride. This conclusion is confirmed by test results and by accidental human exposure.