Reaction mass of bis(trimethoxysilylpropyl)methylphosphonate and (trimethoxysilylpropyl)methylmethyl phosphate

Endpoint summary

Description of key information

The substance is a multi-constituent substance containing two constituents, (trimethoxysilylpropyl)methylmethylphosphonate (Constituent 1) and bis(trimethoxysilylpropyl)methylphosphonate (Constituent 2).

Since the submission 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/substance as a whole as discussed below:

The substance is a liquid at standard temperature and pressure, no melting point was obtained using a differential scanning calorimetry, but glass transition temperature at about -108°C was obtained. It has a measured boiling point of 238.4°C. It has a measured density of 1.14754 g/cm³ at 20°C and a measured vapour pressure of 124 Pa at 20°C and 161 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 119°C and a measured boiling point of 238.4°C. It has a measured auto-ignition temperature of 293°C at 774.4 mmHg (1032 hPa) and is not explosive and not oxidising on the basis of chemical structure.

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

In contact with water, all of the constituents of the substance react rapidly (half-life of <12 hours at pH 7) to produce (trihydroxysilylpropyl)methylmethylphosphonate (HP1) and bis(trihydroxysilylpropyl)methylphosphonate (HP2) as silanol hydrolysis products for Constituent 1 and Constituent 2 respectively according to the following equations. The other hydrolysis product is methanol for both constituents. The reactions are shown in the attached figure in Section 13.

C₈H₂₁O₆PSi + 3H₂O → C₅H₁₅O₆PSi + 3CH₃OH (Constituent 1)

C₁₃H₃₃O₉PSi₂ + 6H₂O → C₇H₂₁O₉PSi₂ + 6CH₃OH (Constituent 2)

Therefore, requirements for testing of water-based physicochemical properties for the constituents are waived on the basis of instability in water. The properties of the silanol hydrolysis products, (trihydroxysilylpropyl)methylmethylphosphonate (HP1) and bis(trihydroxysilylpropyl)methylphosphonate (HP2) and methanol are assessed instead.

However, the key physicochemical properties of the constituents were predicted with the use of validated QSAR estimation methods. Constituent 1 has predicted vapour pressure of 0.077 Pa at 25°C, log K_ow of 0.3 at 20°C and water solubility of 1.0E+06 mg/L at 20°C. Constituent 2 also has predicted vapour pressure of 2.5E-04 Pa at 25°C, log K_ow of -0.2 at 20°C and water solubility of 4.3E+04 mg/L at 20°C.

The saturation concentration in water of the silanol hydrolysis products are limited by condensation reactions to approximately 1000 mg/L for HP1 and 100-500 mg/L for HP2. However, it is very hydrophilic (calculated solubility is 1E+06 mg/L for both HP1 and HP2 at 20°C using a QSAR method), have predicted log K_ow values of -2.8 and -4.0 for HP1 and HP2 respectively. The predicted vapour pressures are 1.2E-06 Pa at 25°C for HP1 and 1.1E-09 Pa at 25°C for HP2.

The silanol hydrolysis products are not expected to be surface active.

 

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).

 

Reference:

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