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Description of key information

Henry's Law Constant (taken from EUSES 2.1.2):

Constituent 1: Calculated HLC at environmental temperature (12°C): 2.1E+04 Pa m3mol-1, 4.3E+04 Pa m3mol-1 at 25°C

Constituent 2: Calculated HLC at environmental temperature (12°C): 2.2E+05 Pa m3mol-1, 4.5E+05 Pa m3mol-1 at 25°C

Key value for chemical safety assessment

Henry's law constant (H) (in Pa m³/mol):
1 200 000
at the temperature of:
25 °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 (HLC). No measured value for this parameter is available. The HLC can be estimated for the constituents of the substance from the ratio of the vapour pressure (VP) to the water solubility (WS).


HLC = (VP x MW)/WS


Where MW is molecular weight.

The estimated HLC for the constituents (taken from EUSES 2.1.2) is reported in Table 4.2.2.

Table 4.2.2: Estimated HLC for the constituents


Predicted water solubility (mg/L)

Predicted vapour pressure (Pa)

Molecular weight (g/mol)

Henry's Law Constant at 25°C (Pa m3mol-1)

Henry's Law Constant at 12°C (Pa m3mol-1)

% abundance of each constituent 

Constituent 1 - 3,3-Diphenylhexamethyltrisiloxane







Constituent 2 - 3,3,5,5-Tetraphenylhexamethyltetrasiloxane







Based on the percentage amount of each constituent in the submission substance, the calculated water solubility and measured vapour pressure for the whole substance and a weighted molecular weight average of 405.16 g/mol, HLC value of 1.2E+06 Pa m3mol-1 at 25°C and 5.6E+05 Pa m3mol-1 at 12°C were obtained for the whole substance.