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Vapour pressure

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The measurement of the vapour pressure of target substance titanium oxychloride itself is being waived, as the substance cannot be isolated from aqueous solutions. It is only possible to measure the vapour pressure of a mixture of titanium oxychloride, hydrochloric acid, and water. Based on a weight of evidence approach resulting from data reported by two MSDS, the vapour pressure is in the range 150 hPa (30°) to 196 hPa (25 °C).

Key value for chemical safety assessment

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Target compound titanium oxychloride is an intermediate hydrolysis product of parent compound titanium tetrachloride. Usually the hydrolysis reaction takes place rapidly and final hydrolysis products titanium dioxide and hydrochloric acid are being formed. Titanium oxychloride can only get stabilised in the system if hydrochloric acid is being added to the in aqueous solution , in this way shifting the chemical equilibrium towards the side of titanium oxychloride. As target substance titanium oxychloride cannot be isolated from aqueous solution, the measurement on the target substance itself is being waived.

In this case the data from two company MSDS are considered as reliable as they coherently report a vapour pressure of the solution containing target chemical titanium oxychloride in the range 150 (30°C) - 196 hPa (25°C). Above stated data reflect the vapour pressure measurement on a mixture of titanium oxychloride, hydrochloric acid, and water, rather than the vapour pressure of the target substance itself. The variation of vapour data is explained by the fact the the percentage of titanium oxychloride, hydrochloric acid and water can vary from case to case. Based on a weight of evidence approach the presented vapour pressure data are being considered as valid.

Note that target chemical titanium oxychloride cannot evaporate from an aqueous solution, as the molecule only can exist inside the aqueous medium, in its hydrated form and in equilibrium with hydrochloric acid. In this context it should be noted that to a certain extent the evaporation of hydrochloric acid might occur from such a chemical system.