Reaction products of [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and triacetoxyvinylsilane.

Endpoint summary

Description of key information

The substance Reaction Products of 3-(2,3-epoxypropoxy)propyltrimethoxysilane and triacetoxy(vinyl)silane is a UVCB substance containing acetoxy/methoxy silanes and siloxanes with alkyl-epoxide and vinyl functional side chains in excess acetic acid and acetic anhydride.

The substance is a liquid at ambient temperature and pressure, with a measured melting point of -15°C and a measured boiling point of 195°C. It has a measured density of 1.1159 g/cm³at 20°C and measured vapour pressure values of 455 Pa at 20°C and 559 Pa at 25°C.

The substance is not classified for flammability according to Regulation (EC) No. 1272/2008, on the basis of a measured flash point of 62.5±0.5°C and measured boiling point of 195°C. It has a measured auto-ignition temperature of 299±3°C, and is not explosive and not oxidising on the basis of structural examination. Also, none of the constituents of the substance is expected to be surface active.

Since the substance is a UVCB substance; two aspects need to be considered in relation to physicochemical properties:

- In the context of raw material handling and safe use (i.e. physicochemical hazards) it is important to understand the properties of the product as a whole;

- For the purposes of assessing environmental fate and behaviour, in the environment, individual constituents are expected to behave independently of each other. It is therefore essential to consider the properties of individual constituents, and whole property data have no real scientific meaning or significance.

In contact with water, the constituents of reaction mass of [3-(2,3-epoxypropoxy)propyl]trimethoxysilane and triacetoxyvinylsilane are susceptible to hydrolysis. All silicon-containing constituents of the substance hydrolyse to [3-(2,3-epoxypropoxy)propyl]silanetriol, vinylsilanetriol, acetic acid and methanol with a hydrolysis half-life of <12 hours at pH 7 and 25°C. At pH 4 and pH 9, the half-lives are less than the pH 7 half-life.

Therefore, the requirements for testing of water-based physicochemical properties for the substance are waived on the basis of instability in water. The properties of the silanol hydrolysis products, [3-(2,3-epoxypropoxy)propyl]silanetriol, vinylsilanetriol, acetic acid and methanol are assessed instead.

Methanol is miscible with water, has low log K_ow (-0.82 to -0.64) and high vapour pressure (12790 Pa at 20°C) (OECD 2004).

Acetic acid is miscible with water (O’Neil 2013), has low log K_ow of -0.17 (Hansch et al. 1995) and a reported vapour pressure of 2090 Pa at 25°C (Daubert and Danner 1985).

The saturation concentrations in water of the silanol hydrolysis products, [3-(2,3-epoxypropoxy)propyl]silanetriol and vinylsilanetriol are limited by condensation reactions to approximately 1000 mg/l. However, both silanol hydrolysis products are very hydrophilic (calculated solubility is 1.0E+06 mg/l using a QSAR method) and with predicted low log K_ow values of -2.6 and -2.0 respectively.

Both silanol hydrolysis products are not expected to be surface active and are much less volatile than the parent substance (vapour pressure values of 1.7E-05 Pa and 1.7 E-02 Pa at 25°C respectively, predicted).

The key physicochemical properties of the silanol hydrolysis products are summarised in the table below.

Table 1.3.3: Predicted physicochemical properties of silanol hydrolysis products

Hydrolysis product	SMILES	Molecular weight (g/mol)	Vapour pressure at 25°C (Pa)	log Kow	Water solubility (mg/l)
[3-(2,3-Epoxypropoxy)propyl]silanetriol	O[Si](CCCOCC1CO1)(O)O	194.26	1.7E-05	-2.6	1.0E+06
Vinylsilanetriol	C=C[Si](O)(O)O	106.15	1.7E-02	-2.0	1.0E+06

 

 

References:

Daubert and Danner (1985). Data compilation tables of properties of pure compounds. American Institute of Chemical Engineers. pp.450, 1985.

Hansch. C., A. Leo and D. Hoekman (1995). Exploring QSAR. Hydrophobic, Electronic, and Steric Constants. ACS Professional Reference Book. Washington, DC: American Chemical Society.

OECD (2004). SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 18 - 20 October 2004, Methanol, CAS 67-56-1

O’Neil (2013). O’Neil M.J. (Editor-in-Chief). The Merck Index: An Encyclopedia of Chemicals, Drugs, and Biologicals, Fifteenth Edition, The Royal Society of Chemistry, UK, 2013.