Registration Dossier
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 silanes.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).
As stated before, oximino silanes are not stable when exposed to water or moisture and undergo rapid hydrolysis. The hydrolysis of the test substance 2-propanone, 2,2',2''-[O,O',O''-(ethylsilylidyne)trioxime] produces 3 moles of acetone oxime and the silanetriol which condensate to higher molecular weight siloxanes. The polymerization products are considered biologically unavailable and the toxicity is driven by acetone oxime.
The toxicity of 2-propanone, 2,2',2''-[O,O',O''-(ethylsilylidyne)trioxime] should be evaluated as the toxicity of acetone oxime.
The results from aquatic toxicity studies are as follow:
- Short-term toxicity to fish. Key study: LC50 (96h) = 696.76 mg/L (basis for effect: mortality) (read-across from the analogue substance acetone oxime).
- Short-term toxicity to aquatic invertebrates: Key study: EC50 (48h) = 678.73 mg/L (basis for effect: mobility) (read-across from the analogue substance acetone oxime)
- Toxicity to aquatic algae: Key study: EC50 (72h) = 315.36 mg/L and NOEC (72h) = 62.34 mg/L (basis for effect: growth rate) (read-across from the analogue substance acetone oxime).
- Toxicity to microorganisms: Key study: EC50 (3h) > 239.78 mg/L (activated sludge, basis for effect: respiration rate) (read-across from the analogue substance Wasox-VMAC2). Key study: EC50 (3h) > 248.06 mg/L (activated sludge, basis for effect: respiration rate) (read-across from the analogue substance Wasox-MMAC2).
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