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Environmental fate & pathways

Hydrolysis

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Description of key information

Hydrolysis half-life at pH 4, 7 and 9: very rapid (much less than the cut-off value of 12 hours).

Key value for chemical safety assessment

Additional information

No hydrolysis study is available for MS-Silane. However, a reliable study equivalent to OECD 111 is available for dichloro(dimethyl) silane which makes up 20 -35% of MS-Silane. This substance is fully hydrolyzed within a few minutes at pH 4, 7 and 9 at 1.5°C. This is also the case for other chlorosilanes for which measured data are available. Therefore, it can be concluded that the submission substance will hydrolyze rapidly under environmentally relevant conditions and no further testing is necessary.

For example, the initial hydrolysis equation for dichlorosilane is expected to be as follows:

 

Me2Si(H)Cl2+ 2H2O → Me2Si(H)(OH)2+ 2HCl

However, the Si-H bond may also be unstable with respect to hydrolysis over a longer timescale; the expected hydrolysis product is methylsilanetriol. Condensation reactions to give siloxane dimers, oligomers and polymers may also occur. A similar reaction process should occur for all chlorinated constituents with the production of silanols, ethylsilanols, or methylsilanols.

 

The following information is taken into account for any hazard / risk / persistency assessment:

Hydrolysis half-life at pH 4, 7 and 9: very rapid (much less than the cut-off value of 12 hours).