3,5,5-trimethylhexanoic acid

Henry's Law constant

Link to relevant study record(s)

Reference

Endpoint:

Henry's law constant

Type of information:

(Q)SAR

Remarks:

and calculation from water solubility and vapour pressure.

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification

Qualifier:

no guideline followed

Principles of method if other than guideline:

Modelling with SRC - HENRYWIN v3.10: Bond estimation method

GLP compliance:

no

Key result

H:

0.104 Pa m³/mol

Temp.:

20 °C

Atm. press.:

1 013 hPa

Remarks on result:

other: from water solubility and vapour pressure

H:

0.286 Pa m³/mol

Temp.:

20 °C

Atm. press.:

1 013 hPa

Remarks on result:

other: QSAR, bond contribution method

H:

0.403 Pa m³/mol

Temp.:

25 °C

Atm. press.:

1 013 hPa

Remarks on result:

other: QSAR, bond contribution method

Estimating Henry's law constant from vapour pressure (0.46 Pa at 20°C) and water solubility (0.7 g/L at 20°C and pH 3.8) results in a value of 0.104 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 3.8), this value corresponds to a dissociation degree of 8.5% according to the Henderson-Hasselbach equation. Therefore, at higher environmental pH Henry's law constant will even be lower.

Conclusions:

Henry's law constant (HENRYWIN v3.10, bond contribution method): 0.286 Pa*m³/mol at 20 °C.
Henry's law constant (from water solubility and vapour pressure): 0.104 Pa*m^3/mol at 20°C.
Concluding, 3,5,5-trimethylhexanoic acid is expected to have a low potential to volatilise from aqueous solutions.

Executive summary:

Using HENRYWIN v3.10, Henry's law constant was calculated according to the bond contribution method to be 0.403 Pa*m³/mol (25 °C; ECT, 2008). The corresponding value according to HENRYWIN (bond contribution) for 20°C is 0.286 Pa*m^3/mol.

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

Estimating Henry's law constant from vapour pressure (0.46 Pa at 20°C) and water solubility (0.7 g/L at 20°C and pH 3.8) results in a value of 0.104 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 3.8), this value corresponds to a dissociation degree of 8.5% according to the Henderson-Hasselbach equation. Therefore, at higher environmental pH Henry's law constant will even be lower.

Concluding, 3,5,5-trimethylhexanoic acid is expected to have a low potential to volatilise from aqueous solutions.

Description of key information

HLC = 0.104 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):

0.104

at the temperature of:

20 °C

Additional information

Using HENRYWIN v3.10 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 v3.10	2	ECT (2008)

The corresponding value according to HENRYWIN (bond contribution) for 20°C is 0.286 Pa*m^3/mol.

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

Estimating Henry's law constant from vapour pressure (0.46 Pa at 20°C) and water solubility (0.7 g/L at 20°C and pH 3.8) results in a value of 0.104 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 3.8), this value corresponds to a dissociation degree of 8.5% 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, 3,5,5-trimethylhexanoic acid is expected to have a low potential to volatilise from aqueous solutions.