Trifluoroacetic acid

Phototransformation in water

Administrative data

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not specified

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1995

Materials and methods

Study type:

indirect photolysis

Principles of method if other than guideline:

This study invastigated the reaction between haloacetates (including TFA) and the most likely strong one electron oxidants to be able to react in atmospheric droplets: the radicals Cl2-, SO4- and OH. Rate constants for the reactions of the radicals with haloacetates were measured by laser-flash photolysis. Decay or formation curves observed subsequent to the flash were average before undergoing least-square analysis to obtain the first order rate constants.All the chemicals used were the purest grade available and all the experiment were performed in aquous medium with water purified.

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

Sodium salt of Trifluoroacetate

IUPAC Name:

Sodium salt of Trifluoroacetate

Details on test material:

- Name of test material (as cited in study report): Sodium salt of Trifluoroacetate (TFA)
- Molecular formula (if other than submission substance): CF3COO-
- Other: test material obtained from Aldrich and of the purest grade available.

Specific details on test material used for the study:

Aqueous solutions of trifluoroacetic acid have naturally low pH and for testing on organisms either the sodium salt or pH adjustment were required.
Sodium trifluoroacetate (TFANa, CAS RN: 2923-18-4) is appropriate as test material in replacement of trifluoroacetic acid because of the following elements :
Both substances are very soluble in water (water solubility at 25°C of 625 g/L for TFANa and 1520 g/L for TFA) and have a low potential of bioaccumulation (QSAR estimated LogKow values of -3.31 for TFANa and 0.79 for TFA). TFANa is a crystalline solid with a low vapour pressure (Vapour pressure at 25°C of 10E-5 Pa for TFANa estimated by QSAR) whereas TFA is a liquid with a medium vapour pressure (12.4 kPa at 20°C). Despite this different volatility, in the aquatic environment, both substances are ionized into the trifluoroacetate anion. This is justified by the fact that trifluoroacetic acid is a strong organic acid with a pKa of 0.23 meaning that it is under dissociated form in all environmental compartments.
Therefore, the environmental bioavailability of the trifluoroacetate moiety should be the same for both substances. Additionally, as the degradability of the cation Na is not applicable, the degradability of the trifluoroacetate moiety is taken into account to assess the degradability of TFA and TFANa.

Study design

Radiolabelling:

no

Sensitiser (for indirect photolysis)

Sensitiser (for indirect photolysis) 1

Type of sensitiser:

NO3 radical

Concentration of sensitiser:

other: 4 different substrates concentrations

Sensitiser (for indirect photolysis) 2

Type of sensitiser:

OH radical

Details on sensitiser:

Use of gamma radiolysis to produce OH (dose rate= 1.22 Gy.s-1 or 4.10 Gy.s-1)

Concentration of sensitiser:

other: 4 different substrates concentrations

Sensitiser (for indirect photolysis) 3

Type of sensitiser:

other: SO4-

Details on sensitiser:

produced by the 248 nm excimer laser-flash photolysis of sodium persulfate solution.

Concentration of sensitiser:

other: 4 different substrates concentrations

Sensitiser (for indirect photolysis) 4

Type of sensitiser:

other: Cl2-

Details on sensitiser:

produced by the reaction of SO4- with Cl-.

Concentration of sensitiser:

other: 4 different substrates concentrations

Results and discussion

Transformation products:

not measured

Any other information on results incl. tables

The relative reactivities of the haloacetates was determined to be :

CH2ClOO- (MCA) > CH2FCOO- (MFA) > CHCl2COO- (DCA) > CHF2COO- (DFA) > CCl3COO- (TCA) > CF3COO- (TFA).

Rate constants for some reactions of radicals with TFA in water in units of L.mol-1.s-1

3.9E+03 for NO3

1.6 +/- 0.1E+04 for SO4-

< 104 for Cl2-

<1E+06 for OH

Applicant's summary and conclusion

Validity criteria fulfilled:

not applicable

Conclusions:

TFA shows a low relative reactivity at the photolysis in aqueous solution.

Executive summary:

The kinetics of the acqueous-phase reactions of the free radicals OH, Cl2- and SO4- with the halogenated acetates, CH2FCOO- (MFA), CHF2COO- (DFA), CF3COO- (TFA) and with CH2ClOO- (MCA), CHCl2COO- (DCA), CCl3COO- (TCA) were investigated. Generally, the reactivity decreases with increasing halogen substitution and is in the order k(OH) > k(SO4 -) > k(Cl2 -), but there is no general relation between the effect on reactivity of chlorine and fluorine substitution.

Rate constants for some reactions of radicals with TFA in water in units of L.mol-1.s-1 were 3.9E+03 for NO3; 1.6 +/- 0.1E+04 for SO4 -; < 104 for Cl2- and <1E+06 for OH. TFA shows a low relative reactivity at the photolysis in aqueous solution.