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Hydrolysis

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Definitive experimental determination of the hydrolysis of boron trifluoride according to EC Method C.7and OECD Test Guideline 111 is, however, not possible due to the speed of the reaction and the lack of a specific, stability-indicating method of analysis for the parent compound.
A study of the more stable dihydrate form of boron trifluoride was conducted and assessment of the hydrolysis rate was made by monitoring degradate concentrations. Measurement of fluoride ion production over a range of pH values (1.2 to 9), using both ion chromatography and an ion-selective electrode, indicated a hydrolytic half-life time of less than 30 minutes for boron trifluoride. Subsequent analysis of boric acid by titration confirmed the rapidity of the reaction.
As a next step, assessment of the stability of the anticipated degradates, fluoroboric acid (tetrafluoroborate) and boric acid, may be worthy of consideration.
With regards to boric acid, the preliminary study showed that at each of pH 1.2, 4, 7 and 9 and 50±0.5ºC, less than 10% hydrolysis had occurred after 5 days, equivalent to a half-life of greater than 1 year under environmental conditions (25°C). No further testing was considered necessary. Boric acid was determined to be hydrolytically stable under acidic, neutral and basic conditions.
Fluoroboric acid was determined to be hydrolytically unstable under similar conditions, reacting to form the ultimate degradation product boric acid and, predominantly, intermediate fluoroborate species. These latter components were not positively identified but, chromatographing as a very broad peak between the tetrafluoroborate and boric acid peaks, and increasing in concentration over the duration of the test, it was considered likely that these were the partially hydrolysed fluoroborate species.

Key value for chemical safety assessment

Additional information

Metal halides are known to hydrolyze readily in the environmentally relevant pH range (pH 4 to pH 10). Boron trifluoride (BF3) reacts with water to give boric acid and fluoroboric acid (HBF4), which then further reacts to produce a number of partially hydrolysed fluoroborate species, boric acid (B(OH)3) and hydrofluoric acid:

HBF4+ H2O → HBF3(OH) + HF

HBF3(OH) + H2O → HBF2(OH)2+ HF

HBF2(OH)2+ H2O → HBF(OH)3+ HF

HBF(OH)3→ B(OH)3+ HF

Definitive experimental determination of the hydrolysis of boron trifluoride according to EC Method C.7and OECD Test Guideline 111 is, however, not possible due to the speed of the reaction and the lack of a specific, stability-indicating method of analysis for the parent compound.

A study of the more stable dihydrated form of boron trifluoride was conducted and assessment of the hydrolysis rate was made by monitoring degradate concentrations. Measurement of fluoride ion production over a range of pH values (1.2 to 9), using both ion chromatography and an ion-selective electrode, indicated a hydrolytic half-life time of less than 30 minutes for boron trifluoride. Subsequent analysis of boric acid by titration confirmed the rapidity of the reaction.

As a next step, assessment of the stability of the anticipated degradates, fluoroboric acid (tetrafluoroborate) and boric acid, may be worthy of consideration.

With regards to boric acid, the preliminary study showed that at each of pH 1.2, 4, 7 and 9 and 50±0.5ºC, less than 10% hydrolysis had occurred after 5 days, equivalent to a half-life of greater than 1 year under environmental conditions (25°C). No further testing was considered necessary. Boric acid was determined to be hydrolytically stable under acidic, neutral and basic conditions.

Fluoroboric acid was determined to be hydrolytically unstable under similar conditions, reacting to form the ultimate degradation product boric acid and, predominantly, intermediate fluoroborate species. These latter components were not positively identified but, chromatographing as a very broad peak between the tetrafluoroborate and boric acid peaks, and increasing in concentration over the duration of the test, it was considered likely that these were the partially hydrolysed fluoroborate species.