Registration Dossier

Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

The registration substance is a multi-constituent substance containing four constituents, trimethoxy(methyl)silane (Constituent 1, CAS No. 1185-55-3), 3-(trimethoxysilyl)-1-propanamine (Constituent 2, CAS No. 13822-56-5), 2,2-dimethoxy-8-{[3-(trimethoxysilyl)propoxy]methyl}-1,6,2-oxazasilocane (Constituent 3) and 9-{[dimethoxy(methyl)silyl]oxy}-3,3,15,15-tetramethoxy-2,7,16-trioxa-11-aza-3,15-disilaheptadecane (Constituent 4).

Since the registration 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 -137°C was obtained. It has a measured boiling point of 96.2°C. It has a measured density of 1.00778 g/cm3 at 20°C and a measured vapour pressure of 2220 Pa at 20°C and 2995 Pa at 25°C.

The registration substance is classified for flammability according to Regulation (EC) No. 1272/2008 on the basis of a measured flash point of 13°C and a measured boiling point of 96.2°C. It has a measured auto-ignition temperature of 276°C 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. The properties of the constituents have been measured or estimated using appropriate methods. In solution, the amine groups present in some of the constituents will protonate; therefore, the estimated log Kow for the unionised form of the constituents were corrected for ionisation using the equation CORR = 1/1 +10A(pH-pKa) [where A = 1 for acids, -1 for bases; pH = pH-value of the environment; pKa = acid/base dissociation constant]. The key physicochemical data for each constituent are reported in the table below.

Table 1.3.2: Key physicochemical properties of constituents of the registration substance

Constituent No

Constituent

SMILES

Molecular Weight (g/mol)

Vapour Pressure (Pa)

Log Kow

Water solubility (mg/L) at 20°C

Constituent 1

Trimethoxy(methyl)silane

CO[Si](OC)(OC)C

136.22

approximately 3000 at 20°C

0.7 at 20°C

9.1E+04

Constituent 2

3-(Trimethoxysilyl)-1-propanamine

NCCC[Si](OC)(OC)OC

179.29

18 at 25°C

0.2 at 20°C (unionised)

-4 at pH 2, -4 at pH 4, -2.8 at pH 7, -0.8 at pH 9 (ionised values)

5.7E+05

Constituent 3

2,2-Dimethoxy-8-{[3-(trimethoxysilyl)propoxy]methyl}-1,6,2-oxazasilocane

CO[Si](CCCOCC1CNCCC[Si](O1)(OC)OC)(OC)OC

383.59

5.9E-04 at 25°C

-0.3 at 20°C (unionised)

-4 at pH 2, -4 at pH 4, -3.3 at pH 7, -1.3 at pH 9 (ionised values)

2.3E+05

Constituent 4

9-{[Dimethoxy(methyl)silyl]oxy}-3,3,15,15-tetramethoxy-2,7,16-trioxa-11-aza-3,15-disilaheptadecane

CO[Si](OC(COCCC[Si](OC)(OC)OC)CNCCC[Si](OC)(OC)OC)(OC)C

519.82

1.4E-05 at 25°C

-1.2 at 20°C (unionised)

-4 at pH 2, -4 at pH 4, -4 at pH 7, -2.2 at pH 9 (ionised values)

1.7E+04

 

In contact with water, all of the constituents of the registration substance react rapidly (half-life of <12 hours at pH 7) to produce the corresponding silanol hydrolysis products and methanol. The reactions are shown in the attached figure. The half-lives are as follows.

Constituent 1: <0.033 h at pH 4, 2.2 h at pH 7 and 0.11 h at pH 9 and 25°C

Constituent 2: 0.2 h at pH 4, 2.6 h at pH 7 and 0.1 h at pH 9 and 20-25°C

Constituent 3: 0.4 h at pH 4, 8 h at pH 7 and 0.1 h at pH 9 and 20-25°C

Constituent 4: 0.3 h at pH 4, 6 h at pH 7 and 0.1 h at pH 9 and 20-25°C

The final hydrolysis products in addition to methanol are:

Hydrolysis product 1 - Methylsilanetriol

Hydrolysis product 2 - (3-Aminopropyl)silanetriol

Hydrolysis product 3 - 5-Oxa-9-aza-1,13-disilatridecane-1,1,1,7,13,13,13-heptol

Therefore, the requirements for testing of water-based physicochemical properties for the constituents of the registration substance are waived on the basis of instability in water. However, the key physicochemical properties for the constituents of the substance are reported in the table above.

The properties of the silanol hydrolysis products and methanol are assessed instead and are reported in the table below.

 

Table 1.2: Key physicochemical properties of silanol hydrolysis products

Hydrolysis product No

Hydrolysis product

SMILES

Molecular Weight (g/mol)

Vapour Pressure (Pa)

Log Kow

Water solubility (mg/L) at 20°C

Hydrolysis product 1

Methylsilanetriol

C[Si](O)(O)O

94.14

0.05 at 20°C

-2.4 at 20°C

1.0E+06 but condensation possible at 1000 mg/L

Hydrolysis product 2

(3-Aminopropyl)silanetriol

NCCC[Si](O)(O)O

137.21

2.5E-04 at 25°C

-2.9 at 20°C (unionised)

-4 at pH 2, -4 at pH 4, -4 at pH 7, -3.5 at pH 9 (ionised values)

1.0E+06 but condensation possible at 1000 mg/L

Hydrolysis product 3

5-Oxa-9-aza-1,13-disilatridecane-1,1,1,7,13,13,13-heptol

OC(COCCC[Si](O)(O)O)CNCCC[Si](O)(O)O

331.47

4.0E-13 at 25°C

-4 at 20°C (unionised)

-4 at pH 2, -4 at pH 4, -4 at pH 7, -4 at pH 9 (ionised values)

1.0E+06 but condensation possible at 1000 mg/L

 

The saturation concentrations in water of the silanol hydrolysis products are limited by condensation reactions that can occur over time at loadings above approximately 1000 mg/L. However, the silanol hydrolysis products are very hydrophilic, predicted key physicochemical results for the silanol hydrolysis products are reported in the table above.

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

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

 

Reference:

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

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