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Diss Factsheets

Administrative data

Hazard for aquatic organisms

Hazard for air

Hazard for terrestrial organisms

Hazard for predators

Additional information

The submission substance is a multi-constituent substance:

Constituents 1a and 1b (cis and trans isomers): 1-[(2-ethylhexyl)oxy]propenyloxydimethoxy (methyl)silane (combined cis and trans isomers) at approximately 75%;

Constituent 2: 2-ethylhexyl 3-[dimethoxy(methyl)silyl]propanoate at approximately 9.5%;

The measured water solubility of the test substance as a whole is <7.8 mg/L, with predicted solubility values ranging from 2.1 to 95 mg/L for the individual constituents. The log Kow values for the constituents range from 4.2 - 5.4:

Constituents 1a and 1b (cis and trans isomers): water solubility = 95 mg/L, and log Kow = 4.2;

Constituent 2: water solubility = 2.1 mg/L, and log Kow = 5.4;


Each constituent hydrolyses rapidly in water (half-lives: Constituents 1a and 1b = ≤5.5 hours and Constituent 2 = 1.6 hours, at pH 7 and 20-25°C). It is therefore likely that the test organisms in each test were exposed primarily to the hydrolysis products.

The products of hydrolysis are:

Constituents 1a and 1b = methylsilanetriol, 1-[(2-ethylhexyl)oxy]prop-1-en-1-ol and methanol. However, 1-[(2-ethylhexyl)oxy]prop-1-en-1-ol, formed by the hydrolysis of the Si-O bond, undergoes tautomerism. This results in rearrangement of the enol-type structure to give the stable ester, 2-ethylhexyl propanoate. In the long-term, the hydrolysis product, 2-ethylhexyl propanoate may undergo further degradation/hydrolysis to the corresponding alcohol and acid; 2-ethylhexylalcohol and propionic acid. The hydrolysis half-life is not known but this is expected to be slow at standard environmental temperature and pH (Mabey W and Mill T, 1978), therefore the assessment will focus on the initial hydrolysis products.

Constituent 2 = 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate and methanol.

The water solubility and log Kow values of the hydrolysis products are varied:

Water solubility [methylsilanetriol]: Above approximately 1000 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated solubility is 1E+06 mg/L (QSAR).

Water solubility [2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate]: Above approximately 10 mg/L condensation reactions can occur over time, limiting the concentration dissolved in water. The calculated solubility is 360 mg/L (QSAR).

Water solubility [methanol]: miscible at 20°C

Water solubility [2-ethylhexyl propanoate]: 24 mg/L at 20°C


log Kow [silanol hydrolysis products of the constituents]: -2.4 to 3.0 at 20°C (QSAR)

log Kow [2-ethylhexyl propanoate]: 4.23 Pa at 20°C

log Kow [methanol]: -0.82 to -0.64

REACH guidance (ECHA 2016, R.16) states that “for substances where hydrolytic DT50 is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself”. TGD and ECHA guidance (EC 2003, ECHA 2016) also suggest that when the hydrolysis half-life is less than 12 hours, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity.

Therefore, the environmental hazard assessment, including sediment and soil compartments due to water and moisture being present, is based on the properties of the silanol hydrolysis product, in accordance with REACH guidance. As described in Section 4.8, the silanol hydrolysis products may be susceptible to condensation reactions.


Consideration of the non-silanol hydrolysis products methanol (CAS 67-56-1) and 2-ethylhexyl propanoate (CAS 6293-37-4)

Methanol: The properties of methanol have been discussed extensively in the public literature. Methanol is considered to be non-toxic to aquatic organisms at the concentrations at which it would have been present in the tests reviewed in this assessment; the short-term EC50 and LC50 values for methanol are in excess of 1000 mg/L (OECD (2004).

2-Ethylhexyl propanoate: No measured data are available for 2-ethylhexyl propanoate. ECOSAR predictions are available for short short-term toxicity to invertebrates and algae. These predictions calculate E(L)C50 values to be 2.04 mg/L for Daphnia and 0.61 mg/L for algae.


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

EC (2003). European Union Technical Guidance Document on Risk Assessment for New and Existing Substances, Part II, European Chemicals Bureau, 2003.

ECHA (2016). Guidance on information requirements and Chemical Safety Assessment. Chapter R.16: Environmental exposure assessment, version 3.0, February 2016.

Conclusion on classification

The substance has reliable short-term E(L)C50 values of >100 mg/L (WAF) in invertebrates and >100 mg/L (WAF) in algae based on a whole substance test. It has a reliable NOEC value of 100 mg/L (WAF) in algae.

The available short-term aquatic toxicity data indicate that there are no effects on aquatic organisms at the maximum loading rate tested of 100 mg/L.

The constituents of the substance hydrolyse rapidly in water. No significant biodegradation of the silanol hydrolysis products is expected.


These data are consistent with the following classification under Regulation (EC) No 1272/2008 (as amended) (CLP):

Acute toxicity: not classified

Chronic toxicity: not classified