Ethyl trifluoroacetate

Hydrolysis

Description of key information

Algae growth range-finding test in combination with an analytical hydrolysis test, OECD 201, GLP, key study, validity 2:
Half-life c.a. 57 minutes.

Key value for chemical safety assessment

Half-life for hydrolysis:

57 min

at the temperature of:

23 °C

Additional information

One valid study report was available to assess the hydrolysis potential of Ethyl trifluoroacetate (TFAE).

This study, assess as the key study, is an algae growth range-finding test in combination with an analytical hydrolysis test. In first instance a range-finding test with algae was performed to provide information about the hydrolysis rate of the test substance under the test conditions. In the range-finding test, three replicates of exponentially growth algal cultures (Pseudokirchneriella subcapitata, initial algal cell density was 10000 cells/mL) were exposed per test group to a control and nominal concentrations of 0.1, 1.0, 10 and 100 mg/L during 72 hours. Samples for chemical analysis were taken from all concentrations at the start, after 24 and 72 hours of exposure. Additional solutions to determine the hydrolysis rate were prepared at 100 mg/L, incubated in the dark with pH adjusted to respectively 4, 7 and 9. The time points of sampling were t=0, t=0.5, t=2, t=4, t=8 and t=24h. From the results of the preliminary study, it was concluded that TFAE rapidly hydrolysed to TFA (half-life of approximatively 57 minutes). In the combined range-finding/hydrolysis test these results were not confirmed since a conversion of TFAE to TFA of only 15 -18% was observed. The explanation for this low TFA recovery is that TFAE was not completely dissolved in the test medium. Since no chemical analysis was performed to measure TFAE this can not be confirmed. However, from 48 hours onwards undissolved particles and or a floating layer were observed at 10 and 100 mg/L. At the end of the test undissolved particles were also observed at 1.0 mg/L. This observation clearly shows that TFAE was not dissolved completely and therefore not hydrolysed to TFA. Based on the results of the preliminary and range-finding studies, it can be concluded that TFAE is rapidly converted to TFA (half-life of TFAE is < 1 hour).

Furthermore, five publications performed between 1953 and 1974 and one recent study (2012) not in accordance with international guidelines, were available. These reports were assessed as not assignable and were flag in weight of evidence. All reports don’t give sufficient experimental details, but support the fact that TFAE is rapidly hydrolysed.

For the five publications, the results were expressed in rate constants. The half-life times were further estimated by the consultant in charge of the dossier.

The report of Gorin et al., published in 1953, described the investigation of the hydrolysis of a serie of ethyl fluoroacetate in 50% acetone and 0,1 M hydrochloric acid. Two methods were performed: the titration method and the conductivity method. It is apparent from the increasing susceptibility of ethyl trifluoroacetate to spontaneous hydrolysis that progressive fluorine substitution facilitates attack by water. This is because the water molecule is a nucleophilic reagent, and attack by such will be favored by inductive withdrawal of electrons from the carbethoxy carbon. The half-life times without catalyst of ethyl trifluoroacetate derived from this publication were 3.6 minutes at 25°C; 6.8 minutes at 15°C and 19.5 minutes at 0°C. 

The report of Winter and Scott, published in 1968, surveys the temperature dependence of the rates of hydrolysis in pure water and deuterium oxide of four esters derived from trifluoroacetic acid. The rate measurements were made using the conductance method. The rate constants which have been measured in light water for the ethyl trifluoroacetate were used for calculated the half-life times. These half-life times were 5.3 hours at 22°C; 8.2 hours at 15°C and 16.4 hours at 5°C.

The report of Barnes et al., published in 1972, investigated the rate of solvolysis of ethyl trifluoroacetate in a series of H2O/D2O mixtures at 9.97°C. The experimental methods for rate determinations were identical to those described in the report of Winter and Scott. The rate constants which have been measured in light water for the ethyl trifluoroacetate were used for calculated the half-life times. These half-life times were 8.1 hours at 15°C; 11.3 hours at 10°C and 16.3 hours at 5°C.

The report of Moffat and Hunt, published in 1956, allows to determine the effect of chain length of both the acid and the alcohol component upon the neutral hydrolysis of n-alkyl esters of perfluorinated acids. A mixture of acetone (70% by volume) and water was used in these experiments. The pseudo first-order rate constants for the ethyl esters of trifluoroacetic can be related quantitatively to molecular weight differences. The 25h-hydrolysis rate constant for ethyl trifluoroacetate was used for calculated the half-life time. This half-life time was 3.6 hours at 25°C.

The report of Bock et al., published in 1974, allows to determine the rates of hydrolysis of some of the thiol esters and phenyl trifluoroacetate in water or aqueous acetone have also been measured. Esters of trifluoroacetic acid react with water at low acid concentrations by the uncatalyzed process. The rate of hydrolysis of ester of trifluoroacetic acid in water at 6°C was used for calculated the half-life time. This half-life time was 14.9 hours at 6°C.

The recent study performed in 2012, used two methodologies to assess the hydrolysis potential of the test substance. The first method was performed in closed bottle with magnetic bar agitation, and the second method was performed in a reactor with four inclined blades agitation at 1100 rpm and 650 rpm. In the first method, only a single species is observed by RMN and a confirmation of the TFA presence was performed. TFAE was not observed during the whole period of the test. The water solubility of the TFAE is lower than the detection limit of the RMN. 75% of hydrolysis was observed after 5 minutes while an insufficient system of mixture is used. After 30 minutes, the totality (c.a. 90%) of the TFAE is converted in TFA. In the second method, the variation of the TFA concentration is linear in function of time. The hydrolysis rate of TFAE is directly related to the speed of dispersion in water of TFAE, therefore to the agitation. The final analysis shows that the totality of TFAE is converted in TFA (92% of hydrolysis). In conclusion, TFAE is poorly soluble in water (<<1g/L or < detection limit by RMN) but the hydrolysis in TFA is rapid, complete, regardless the initial concentration, and only function of agitation.