Propanenitrile, 2,3,3,3-tetrafluoro-2-(trifluoromethyl)-

Hydrolysis

Description of key information

The rate limiting step for hydrolysis of C4 F-isonitrile hydrolysis is diffusion into water. The half-life for hydrolysis of dissolved material is <12 hours at ambient temperature (ca. 23 °C)

Key value for chemical safety assessment

at the temperature of:

23 °C

Additional information

The stability of C4 F-isonitrile in ecotoxicity test media was studied. Gas was introduced into the test system vessels at ambient temperature (ca. 23 °C at this location) and allowed to diffuse into the test media up to the maximum solubility. Once in solution, the dissolved isonitrile hydrolyzed to form the corresponding amide.

For ISO medium, 32% of the gaseous isonitrile dosed into the test system vials was hydrolyzed to amide after 72 hours of incubation without shaking. The measured aqueous levels of amide were over 1000 times greater than the measured levels of isonitrile. The plot of aqueous amide concentration versus time produced a linear fit suggestive of zero-order kinetics with a combined diffusion/hydrolytic rate constant of 511 ng/mL per hour.

For M2 medium, 94% of the gaseous isonitrile dosed into the test system vials was hydrolyzed to amide after 48 hours, under the experimental conditions of this study (ambient temperature with continuous, gentle mixing). Measured levels of amide were over 500 times greater than the isonitrile. A combined dissolution/hydrolytic rate constant could not be determined as only three time points were investigated.  

It is evident from the above study, as well as from the water solubility and Henry's Law constant studies, that mixing has a strong effect on dissolution of gaseous isonitrile into aqueous matrices. This is typical for substances that do not mix well into water. Also, concentration of isonitrile in the gas phase has an impact on dissolution as shown by the difference in loss from gas phase in the water solubility and Henry's law experiments.  For purposes of exposure modeling, the remaining mass of isonitrile at the end of the M2 medium incubation, six percent at 48 hours, is used to estimate an approximate hydrolytic half-life.  Remaining isonitrile is roughly one-sixtienth of the starting amount, indicating that ca. four half-lives had passed during the 48-hour incubation period.  As shown, distribution from the gas phase to the aqueous phase is rate-limiting for the overall process of dissolution and hydrolysis.  This limitation is also evidenced by the measured Henry's Law constant of 590 atm m³/mole.  The gentle mixing used in the M2 experiment is not expected to fully compensate for slow dissolution kinetics.  The estimated half-life of 12 hours is therefore an overestimate of the time needed for hydrolysis of dissolved material.