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Endpoint summary

Description of key information

The substance is a multi-constituent substance containing, 1-[(1Z)-1-(2-ethylhexyloxy)prop-1-enyloxy]-1,1-dimethoxy-1- silaethane (Constituent 1a), 1-[(1E)-1-(2 ethylhexyloxy)prop-1-enyloxy]-1,1-dimethoxy-1- silaethane (Constituent 1b) and 2-ethylhexyl-3-[dimethoxy(methyl)silyl]propanoate (Constituent 2). Constituent 1a and Constituent 1b are geometric isomers [1-[(2-ethylhexyl)oxy]propenyloxydimethoxy (methyl)silane (combined cis and trans isomers)]. It has not been possible to separate these isomers and no differences in physicochemical properties have been observed.

Since the substance is a multi-constituent substance, two aspects need to be considered in relation to physicochemical properties:

1) In the context of raw material handling and safe use it is important to understand the properties of the product as a whole

The substance is a liquid at room temperature and pressure, with a freezing temperature of <-20°C and a measured boiling point of 206±1°C at 1000.2 – 1017 hPa. It has a measured relative density of 0.94 at 20±0.5°C. The vapour pressure of the whole substance was measured to be 1.0 Pa at 20°C and 1.8 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 107±2°C and a measured boiling point of 206±1°C at 1000.2 – 1017 hPa. It has a measured auto-ignition temperature of 215°C at 1013.2 -1027 hPa, and is not explosive and not oxidising on the basis of chemical structure. Also, none of the constituents of the substance are expected to be surface active.

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

The predicted key physicochemical properties of the individual constituents are shown in Table 1.1

Table 1.1: Predicted key physicochemical properties of constituents of the substance

Constituent Number	Constituent name	SMILES	Molecular weight (g/mol)	Vapour pressure (Pa ) at 25°C	log Kow at 20°C	Water solubility (mg/L) at 20°C
1a	1-[(1Z)-1-(2-ethylhexyloxy)prop-1-enyloxy]-1,1-dimethoxy-1- silaethane	CCCCC(CO/C(=C/C)/O[Si](OC)(OC)C)CC	290.48	0.073	4.2	95
1b	1-[(1E)-1-(2 ethylhexyloxy)prop-1-enyloxy]-1,1-dimethoxy-1- silaethane	CCCCC(CC)CO\C(O[Si](C)(OC)OC)=C/C	290.48	0.073	4.2	95
2	2-Ethylhexyl 3-[dimethoxy(methyl)silyl]propanoate	CCCCC(COC(=O)CC[Si](OC)(OC)C)CC	290.48	0.065	5.4	2.1

In contact with water, the constituents react rapidly. Each constituent contains two or three Si-OR’ groups which can hydrolyse to form Si-OH and ROH.

The predicted half-lives for degradation of Constituents 1a and 1b (cis and trans isomers) are ≤5.5 h at pH 7, ≤0.3 h at pH 4 and ≤0.1 h at pH 9 and 20-25°C. The hydrolysis products are 2-ethylhexyl propanoate (1 mole), methanol (2 moles) and methylsilanetriol (1 mole).

The predicted half-lives for degradation of Constituent 2 are 1.6 h at pH 7, 0.1 h at pH 4 and 0.03 h at pH 9 and 20-25°C. The hydrolysis products are 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate (1 mole) and methanol (2 moles).

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 hydrolysis products, methylsilanetriol and 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate, 2-ethylhexylpropanoate and methanol are assessed instead.

The saturation concentration in water of the silanol hydrolysis products, methylsilanetriol and 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate, are limited by condensation reactions that can occur over time at loadings above approximately 1000 mg/L and 10 mg/L respectively.

The silanol hydrolysis products are not expected to be surface active. The physicochemical properties of the hydrolysis products are reported in Table 1.2.

Table 1.2: Predicted physicochemical properties of hydrolysis products

	Silanol hydrolysis product		Non-silanol hydrolysis product
	Methylsilanetriol, CAS 2445-53-6	2-Ethylhexyl 3-[dihydroxy(methyl)silyl]propanoate	2-Ethylhexyl propanoate, CAS 6293-37-4	Methanol, CAS 67-56-1
SMILES	C[Si](O)(O)O	CCCCC(COC(=O)CC[Si](O)(O)C)CC	CCCCC(COC(=O)CC)CC	CO
Vapour pressure	5.0E-02 Pa at 25°C	3.3E-06 Pa at 25°C	19 Pa at 25°C	12790 Pa at 20°C
log Kow at 20°C	-2.4	3.0	4.23	-0.82 to -0.64
Water solubility (mg/L) at 20°C	1.0E+06	360	24	Miscible