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Environmental fate & pathways

Hydrolysis

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Reference
Endpoint:
hydrolysis
Data waiving:
study technically not feasible
Justification for data waiving:
other:

In aqueous solutions, hydrolysis of both the halide ligands and the cyclopentadiene rings occur. The rate of these two processes is highly dependent on both the transition metal ion, the nature of the halide ligand, and the solution pH.

In unbuffered solutions of water (pH ~ 3) or in 0.32 M KNO3 reversible rapid hydrolysis of the first chloride ligand occurs in Cp2MCl2 (M = Ti,V, Mo, Zr) to give an aquated intermediate, followed by a slower dissociation of the second chloride [50 min M = Ti; 30 min M = V;24 min M = Zr; 6.7 min M = Mo], Fig. (2a). From Fig. (2a), it can be seen that both the concentration and solution pH will affect the equilibrium reactions, with the rate of chloride hydrolysis expected to be decreased at low pH and in high concentrations of salt since the equilibrium lies in favour of the metallocene dichloride. While detailed studies of the hydrolysis of other halide or acido ligands has not been reported, all studies are consistent with a similar rapid dissociation of these ligands to generate aquated species in which the Cp ligands remain coordinated to the metal at low pH.

It has also been stated that loss of chloride or acido ligand seems to be associated with dissolution of the complexes.

The estimated half lives for loss of the Cp rings in Cp2MCl2 (M = Ti) water or in 0.32 M KNO3 at 37 °C and at low pH (pH ~ 3), are as follows: Cp2TiCl2 (t1/2 = 57h).

Figure 2a and 2b are depicted under illustration.

Description of key information

The endpoint is waived as it was not feasible to undertake hydrolysis characterization testing as detailed within the regulatory methods. Supporting literature studies are included.

Key value for chemical safety assessment

Additional information