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Physical & Chemical properties

Vapour pressure

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vapour pressure
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.
Principles of method if other than guideline:
The test apparatus involve the use of a Carius tube.
GLP compliance:
Type of method:
other: Carius tube
Key result
Test no.:
20 °C
Vapour pressure:
113.7 hPa

Vapour pressure in mmHg (PSI) at 20°C

Test 1         

Test 2          

Test 3

85.30 (1.65)

85.30 (1.65)   

85.30 (1.65)

A vapour pressure value of 113.7 hPa at 20°C was determined for the substance in a reliable study conducted according to generally accepted scientific principles, but not according to GLP.

Description of key information

Vapour pressure [trimethoxysilane]: 11370 Pa at 20°C

Vapour pressure [silanetriol]: negligible

Vapour pressure [silicic acid]: negligible

Vapour pressure [methanol]: 12790 Pa at 20°C

Key value for chemical safety assessment

Vapour pressure:
11 370 Pa
at the temperature of:
20 °C

Additional information

A measured vapour pressure value of 11370 Pa (approximately 11400 Pa) at 20°C was determined for the submission substance using a relevant test method, but not in compliance with a known quality system. The result is considered to be reliable and is selected as key study.

The key study is supported by a vapour pressure approximately 7500 Pa at 20°C which was obtained for the substance using a temperature-vapour pressure correlation estimation method.

In available secondary sources to which reliability could not be assigned, vapour pressure values of 10130 Pa at 25°C, 930 Pa at 24.4°C and 10570 Pa at 26.5°C were reported for the substance.

In a disregarded study, a vapour pressure value of approximately 975000 Pa at 176.8°C was determined for the substance. The result is however disregarded because the study was conducted at high elevated temperature and there was observed decomposition before and during the experiment.

In contact with water, trimethoxysilane reacts very rapidly to form silanetriol and silicic acid as intermediate and ultimate hydrolysis products respectively. The other hydrolysis products are methanol and hydrogen gas.

Both silicon-containing hydrolysis products are expected to have negligible vapour pressure values.

Methanol has a reported vapour pressure of 12,790 Pa at 20°C (OECD 2004).


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