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It is well known that triacetoxisilane undergoes rapid hydrolysis in aqueous or moist environments to acetic acid and trisilanol.

The confirm that hydrolysis of acetoxysilanes is fast, the test of hydrolysis of propyl triacetoxysilane in water was performed. It was measured, that the process was very fast. The half-life at different pH of propyltriacetoxysilane was determined to be < 37.5 seconds since the test item was completely hydrolysed at 150 seconds after the initial contact with water.

As it is stated in different publications, silanols hydrolyse well in water and the carbon- bounded substituents can have profound effects on the rate of hydrolysis. (Arkles B., Chemtech 1977; Pluddemann E.P., Plenum Press NY, 1982; Kay, B.D. and Assink R.A, J. Non-Cryst. Solids, 1988).

The rates of hydrolysis of the alkoxy groups are generally related to their steric bulk: CH3O>C2H5O> t-C4H9O and a methoxysilane hydrolyzes at 6-10 times rate of an ethoxysilane. Smith (Smith K. J. Org. Chem 1986) proved that increased organic substitution enhances the hydrolysis rate Me3SiOMe> Me2Si(OMe)2> MeSi(OMe)3.

During the performed hydrolysis test, the condensation and polimerysation of the molecules formed in hydrolysis were observed too. It was observed as the phase separation. Unfortunately, this phase separation caused the technical difficulties of the determination of the molecular weight of larger condensation products. It was possible to determined MW of smaller condensates which still are in solutions. Their average MW were between 604-695.

This phase separation as a result of condensation was described by Arkles. The hydrolysis of propyltrimetoxysilane showed that oligomers are formed and branched structures presages phase separation (Arkles B. et al, Silanes and Coupling Agents, 1992).

Taking in account both, the hydrolysis and condensation, it is expected that the observed in the hydrolysis test phase changed product contains large chain polymers with MW>1000.

Authors showed that molecules of MW>1000 cannot be biologically available (Van Gestel et a, Reg. Toxicol. and Pharmacol., 1985, 5, 422-31 and Zitko V, Handbook of Environmental Chemistry, v. 2 221-29).

Stability: Hydrolysis: Key study: Based on experimental results on test item, Propyltriacetoxysiloxane rapidly hydrolyses into acetic acid and the forming silanol (trihydroxypropylsilane, which undergoes fast kinetic polycondensation reactions). The half-life time at pH 1.2, 4, 7 and 9 was determined to be < 37.5 seconds.

Biodegradation: Key study: Based on read-across approach from experimental data on analogue Methyltriacetoxysilane, Propyltriacetoxysilane was determined to be readily biodegradable. According to column 2 of REACH Annex IX, the simulation testing in surface water, sediment and soil were not necessary to be conducted since the substance is readily biodegradable.

Bioaccumulation: According to the column 2 of REACH Annex IX, the study needs not to be conducted since the substance has a low potential for bioaccumulation (log Kow < 3).

Transport and distribution: According to the column 2 of REACH Annex VIII, the study does not need to be conducted since the substance is expected to have low potential for adsorption based on the low octanol-water partition coefficient (log Kow < 3).

Nevertheless, base on the KOCWIN v2.00, MCI calculateion method, soil adsorption of propyltriacetoxysilane was estimated to be: Koc = 15.89 L/kg and Log Koc = 1.201.