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Registration Dossier
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EC number: 611-631-1 | CAS number: 58190-57-1
Endpoint summary
Administrative data
Description of key information
Additional information
Monomeric silicon chemicals are known as silanes. A silane that contains at least one silicon carbon bond, (e.g -Si-CH3) is an organosilane. They normally contain two different types of reactive groups: the hydrolysable groups such as methoxy, ethoxy or acetoxy groups and the organo-functional group, such as epoxy, amino, methacryloxy, or sulfido. It is well known that the Si-OR bonds hydrolyse readily with water, even if only with moisture absorbed on the surface, to form silanol Si-OH groups. These silanol groups can then condense with each other to form polymeric structures with very stable siloxane Si-O-Si bonds.
Previously, to confirm that hydrolysis of silanes is fast, several hydrolysis tests have been conducted in analogue substances. In the hydrolysis test performed on propyltriacetoxysilane, the process was very fast. The half-life at different pH of test item was determined to be < 37.5 seconds since it completely hydrolysed at 150 seconds after the initial contact with water.
Moreover, the hydrolysis test performed on two acetone oxime silanes, more than 50% of the components hydrolysed in less than 0.75hafter starting the dissolution of the test substance at 25 ºC and independently of the pH.
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 hydrolysis test performed with propyltriacetoxysilane, the condensation and polymerisation 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).
The results for environmental fate and pathways are as follows:
Hydrolysis: Key studies: Based on the read-across approach from experimental results on VAC3 and MAC3 performed in accordance with EU method C.7. (GLP studies), the half-life of EAC3 was determined to be less than 1 hour at pH 4, 7 and 9 and at 25 ºC. The substance is hydrolytically unstable in water.
Biodegradation in water: Weight of evidence: Based on the read-across approach from experimental results on the analogue substances Wasox-VMAC2 and Wasox-MMAC2 (OECD Guideline 301B, GLP studies), the test item EAC3 was also determined to be not readily biodegradable. Weight of evidence: Based on read-across approach from experimental data on the hydrolysis product acetone oxime (OECD Guideline 301D, GLP study), EAC3 was expected to be not readily biodegradable.
These results were supported by the prediction performed with EPI-Suite, EPA (USA) v4.1 (BIOWINN v4.10), where the EAC3 was determined to be not readily biodegradable.
Biodegradation in sediment: Data waving (other justification): In accordance with column 2 of REACH Annex IX, the study does not to be conducted since direct and indirect exposure of sediment is unlikely.
Biodegradation in soil: Data waving (other justification): In accordance with column 2 of REACH Annex IX, the study does not to be conducted since direct and indirect exposure of soil is unlikely.
Bioaccumulation: aquatic/sediments: Key study: Based on the read-across approach from the experimental results on the analogue substance acetone oxime (EPISuite v4.1 / BCFWIN v3.1, US EPA ), the BCF of EAC3 was determined to be 3.162 L/Kg w/w.
Adsorption: Key studies: Based on the read-across approach from experimental data on analogue substance Wasox-VMAC2 and Wasox-MMAC2 (OECD Guideline 121, GLP studies), the study was determined to be not technically feasible on EAC3. The soil adsorption coefficient (Koc) of EAC3 was calculated to be 85490 (log Koc= 4.932). Estimation method: EPISuite v4.1 / KOCWIN v2.00 (US EPA).
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