Nonanoic acid

Henry's Law constant

Link to relevant study record(s)

Reference

Endpoint:

Henry's law constant

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

supporting study

Study period:

December 2020

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Justification for type of information:

For derivation of Henry's law constant, it is an accepted estimation method to use the vapour pressure (at 20 °C; in Pa) in the numerator and the water solubility (at 20 °C; in mol/m^3) in the denominator.

Reason / purpose for cross-reference:

reference to other study

Reason / purpose for cross-reference:

reference to other study

Key result

H:

0.065 Pa m³/mol

Temp.:

20 °C

Atm. press.:

1 013 hPa

Remarks on result:

other: Calculated from experimental vapour pressure (at 20 °C) and water solubility (at pH 4.2)

Conclusions:

Henry's law constant (from water solubility and vapour pressure; 20 °C): 0.065 Pa*m^3/mol

Executive summary:

Estimating Henry's law constant from vapour pressure (0.123 Pa at 20°C) and water solubility (0.3 g/L at 20°C and pH 4.2) results in a value of 0.065 Pa*m^3/mol at 20°C. Based on a pKa of 4.8 and the pH at which the water solubility had been determined (pH 4.2), this value corresponds to a dissociation degree of 20.1% according to the Henderson-Hasselbach equation. Therefore, at higher environmental pH Henry's law constant will even be lower.

Description of key information

HLC = 0.065 Pa*m³/mol at 20 °C (calculated from water solubility and vapour pressure)

Key value for chemical safety assessment

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

0.065

at the temperature of:

20 °C

Additional information

Using HENRYWIN v3.20 Henry's law constant was calculated according to the bond contribution method to be 0.403 Pa*m³/mol (25 °C; ECT, 2008):

HLC (Pa*m³/mol)	Temperature (°C)	Method	Reliability	Reference
0.403	25	estimated: SRC - HENRYWIN v3.20	4	ECT (2010)

Because the submission substance is an acid (pKa 4.8), this will overestimate Henry's law constant for the dissociated fraction.

Estimating Henry's law constant from vapour pressure (0.123 Pa at 20°C) and water solubility (0.3 g/L at 20°C and pH 4.2) results in a value of 0.065 Pa*m^3/mol at 20°C. Based on a pKa of 4.8 and the pH at which the water solubility had been determined (pH 4.2), this value corresponds to a dissociation degree of 20.1% according to the Henderson-Hasselbach equation. Therefore, at higher environmental pH Henry's law constant will even be lower.

Therefore, as a key result for environmental exposure and risk assessment the value derived from water solubility and vapour pressure is used.

Concluding, n-nonanoic acid is expected to have a low potential to volatilise from aqueous solutions.