2-butanone-O,O',O''-(phenylsilylidyne)trioxime

Endpoint summary

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Results available from other studies:

The test substance is miscible in all proportions with standard fat at 37°C and has a high (predicted) partition cofficient (log Pow = 11.05), indicating that the substance is potentially bioavailable, and if it is absorbed it has the potential to bioaccumulate. The substance is reactive on exposure to water, hydrolysing rapidly to methyl ethyl ketoxime. It is, therefore, possible that methyl ethyl ketoxime (butanone oxime), rather than the test substance, would be available for adsorption. The oral toxicity studies provided evidence of oral absorption and systemic distribution in the form of clinical signs, changes in blood parameters and macroscopic findings. In the acute dermal study, there was no evidence of adsorption by the dermal route. In the 28-day oral study there were no signs of metabolism or renal excretion. In addition, as the anaemia observed was shown to be reversible in the recovery animals, the test substance or hydrolysis products have been shown not to bioaccumulate. In the mutagenicity studies, there was no observed difference in the presence or absence of S-9 mix and no major differences in the mitotic indices, providing no evidence of metabolism.

Conclusion:

Oral toxicity studies provided evidence of oral absorption and systemic distribution. There was no evidence of metabolism or excretion. There was also no evidence of dermal absorption. There was no evidence of toxicity or clastogenic activity in the mutagenicity studies, either in the presence or absence of metabolic activation.

Hydrolysis and condesation:

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, a hydrolysis test have been conducted with the test substance 2-butanone-O-O’-O’’-(phenylsilylidyne)trioxime and the half-life at pH 4, 7 and 9 at 20 ºC was determined to be less that 5 min.

In the hydrolysis test performed on propyltriacetoxysilane, the process was also 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 0.75h after 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 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).

As stated before, oximino silanes are not stable when exposed to water or moisture and undergo rapid hydrolysis. The hydrolysis of 2-butanone-O-O’-O’’-(phenylsilylidyne)trioxime produces 3 moles of butanone oxime and the silanetriol which condensate to higher molecular weight siloxanes. The polymerization products are considered biologically unavailable and the toxicity is driven by butanone oxime. The toxicity of 2-butanone-O-O’-O’’-(phenylsilylidyne)trioxime could be evaluated as the toxicity of butanone oxime.