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

Endpoint summary

Additional information

Stability of the C4 fluorinated isonitrile was addressed in three phototransformation studies. In the atmosphere the isonitrile undergoes reaction with hydroxyl radical in the gas phase. The rate of reaction was monitored v. HFC-125 or methane, with the isonitrile reacting less quickly than either. The average lifetime obtained by comparing relative reaction rates with known atmospheric lifetimes of the reference compounds is ca. 30 years.

A study of hydrolytic stability in aquatic toxicology test media is available, and additional information on hydrolytic stability is derived from water solubility, Henry's Law constant, and octanol-water partition coefficient (log P) studies. The isonitrile is hydrolytically unstable, forming the corresponding fluorinated amide when held in contact with aqueous phases. In the water solubility study a pure isonitrile gas phase comprising ca. 25% of total volume was shaken with water for up to 12 days. Test vials were held upside-down during shaking so that the headspace was in contact with the glass and thereby prevent gas from leaking through the cap. The average measured concentration was 272 µg/L in this period, but the amount of isonitrile in the headspace was reduced by 75% in the same time period. The Henry's Law constant experiment was done similarly, but contained larger headspaces with dilute isonitrile (5000 ppmv). With the more dilute gas, distribution from the gas phase into the water with concomittant hydrolysis was less favorable. Concentrations of isonitrile in the headspace were unstable only at the smallest headspace volume (ca 25%) and declined by 13% over 11 days of shaking. However, the same degradation product was detected by HPLC analysis of water samples

in both experiments. The presence of the amide was confirmed in the log P experiment although concentrations were not quantified. The isonitrile is also subject to hydrolysis in water-saturated octanol, and may also form imidate adducts which could not be detected by the analytical methodology used in the log P experiment. Average reduction of nitrile in headspace gases was 60%. The fluorinated amide was not confirmed in the Henry's Law or water solubility experiments; however, the results obtained in these other experiments were consistent with the log P result. The exact rate of hydrolysis is not well defined, since the process involves distribution to the aqueous phase as a prior step before hydrolysis. 

In addition to these studies, feasibility studies were conducted to evaluate the potential to perform aquatic toxicology tests on the gas. Small volumes of gas were injected into sealed containers completely filled with medium, and then held for 48 hours. Time points for chemical analyses were as soon as possible after test vessel assembly, at 24 hours, and at 48 hours. The parent was analyzed in the limited headspace and in solution, and the hydrolysis product was measured in solution only. Average mass balances during these tests were 98-108%, indicating that all parent and degradation product were recovered. In the daphnia medium experiment (unshaken), ca. 75% of the parent gas remained in the headspace. The aqueous concentration of parent declined from 200 µg/L to 30 µg/L within 48 hours, while the concentration of hydrolysis product increased from 700 µg/L at time zero to 40,000 µg/L at 48 hours. The total process (entry into the aquatic phase and hydrolysis) showed first-order kinetics, indicating that the process was limited by transport into the dissolved phase. In the test of algae medium (with shaking), ca. 80% of parent was lost from the headspace within 24 hours and 90% within 48 hours. The initial and 24-hour parent aqueous concentrations were similar (ca. 600 and 800 µg/L) but declined at 48 hours (ca. 200 µg/L). The remaining mass of parent had been converted to dissolved hydrolysis product (ca. 90 % by 48 hours, >100 mg/L). The overall process did not follow first-order kinetics, which is expected since the flasks were shaken and limitation by transport was at least partially mitigated. The extent of increase in the hydrolysis product's concentration indicates that the parent can only be maintained in solution by replacement from an adequately large headspace, while concentration of the hydrolysis product would increase throughout the test. If the headspace were removed, the remaining dissolved parent would quickly hydrolyze to form the amide. Consistent test concentrations of the parent and its hydrolysis product cannot be maintained even in a closed container.

 

Given the relatively long atmospheric lifetime of C4 fluorinated isonitrile and the ready hydrolysis of the vapor when in contact with liquid water, the possibility of hydrolysis in the atmosphere cannot be discounted. However, no information on rate is available for the atmospheric compartment. The net effect of hydrolysis in the atmosphere would be to reduce atmospheric lifetime of the isonitrile, with deposition of amide to the terrestrial and the aquatic compartments.