Tetramethylsilane

Henry's Law constant

Description of key information

Henry's Law Constant:

Calculated HLC at 12°C: 2.4E+5 Pa m³/mol

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):

240 000

at the temperature of:

12 °C

Additional information

The transfer of a substance from the water phase to the gas phase can be estimated by means of the Henry’s Law Constant. No measured value for this parameter is available for tetramethylsilane. The Henry’s Law Constant and the K_air-water can be estimated from the ratio of the vapour pressure to the water solubility (ECHA 2010, R16):

HLC = VP x MW/WS 

K_air-water = HLC/R x T

Where:

HLC is the Henry’s Law constant in Pa m³/mol

VP is the vapour pressure in Pa at 285 K

MW is the molecular weight in g/mol

WS is the water solubility in mg/L at 285 K

R is the gas constant = 8.314 Pa m³mol^-1K^-1

T is the temperature at the air-water interface = 285 K

K_air-water is the air-water partitioning coefficient

K_air-water has been calculated for tetramethylsilane; the results are shown in Table 4.2.2 and indicate high volatilisation from water.

Table 4.2.2. Volatilisation of tetramethylsilane

Parameter (at 285 K)		Tetramethylsilane
VP^a		44700
MW		88.23
WS^b		16.3
HLC		242 000
Kair-water		102

 

Notes:

a - Calculated from the vapour pressure of 79500 Pa at 20°C using the equation:

 VP₂ = VP₁ x e^{((5000/R)x(1/T1 -1/T2))}

 

b Calculated from the predicted water solubility of 19.6 mg/L at 25°C using the equation:

WS₂ = WS₁ x e^{((10000/R)x(1/T1 -1/T2))}

The calculated Henry’s Law constant of 2.4E+5 Pa m³mol^-1 at 12°C suggests that air will be the main compartment to which tetramethylsilane partitions. Testing for adsorption properties is technically not feasible due to the high volatility of the substance and its slight solubility in water. However, exposure of the aquatic compartment will be minimal.