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Physical & Chemical properties

Endpoint summary

Administrative data

Description of key information

Additional information

HD4 is a liquid at standard temperature and pressure, with a melting point of <-20°C, and a boiling point of 134 to 135°C. It has a density of 0.98 g/cm3at 20°C and a viscosity of 6.9 mm²/s (static) at 20°C. The measured vapour pressure is 479 Pa at 20°C.

The substance is classified as flammable on the basis of a flash point of 27.9°C. It has a self-ignition temperature of 270°C, is not explosive and is not oxidising.

In contact with water it reacts very rapidly (half-life 2.2 min at pH 7 and 22.5°C); this initial half-life relates to opening of the siloxane ring. The end product of the hydrolysis is methylsilanetriol; hydrogen gas is produced as a by-product of the reaction. At high concentrations, condensation products of methylsilanetriol and of intermediate hydrolysis products can form, but this is not relevant for environmental concentrations. The intermediate products of hydrolysis are linear siloxanols and methylsilanediol.

Methylsilanetriol is predicted to be miscible with water, with low log Kow(-2.4, predicted). It is not surface active and does not undergo significant dissociation within the environmentally relevant range. It is less volatile than the parent substance (vapour pressure = 0.05 Pa, predicted).

Predicted values for the key physicochemical properties of the expected intermediate and final hydrolysis products are shown in the table below.

Table: Key physicochemical properties of some expected hydrolysis products of HD4

 

SMILES

VP / Pa at 25°C

WS / mg/l

Log Kow

Hydrolysis at pH 7 and 20-25°C / h

Intermediate HP1

[Si](O[Si](O[Si](O)C)C)(O[Si](O)C)C

1.7E-04

7.5E+02

2.5

0.2 h

Intermediate HP2

[Si](O[Si](O[Si](O)C)C)(O)C

3.8E-03

1.3E+04

1.6

0.4 h

Intermediate HP3

C[Si](O)O[Si](O)C

1.3E-01

1.9E+05

0.6

1.0 h

Methylsilanediol

C[Si](O)O

6.5 Pa

7.6E+05

-1.0

n/a

Methylsilanetriol

C[Si](O)(O)O

0.05 Pa

1.0E+06

-2.4

n/a