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Environmental fate & pathways

Hydrolysis

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Description of key information

In contact with water the substance will hydrolyse rapidly.

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Additional information

Boron trifluoride diethyl ether is known to rapidly decompose on contact with water to form boronfluoride dihydrate (H3O+[BF3(OH)]-) and diethyl ether (BASF AG, 1987) as a first step. Diethyl ether is relatively unreactive and may only hydrolyse at elevated temperatures with either acid or base catalysis (Keeley in Kirk-Othmer 1980). Hydrolysis under environmental conditions is therefore unlikely. Metal halides are known to hydrolyze readily in the environmentally relevant pH range (pH 4 to pH 10). Boron trifluoride (BF3) reacts instantly 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+ H2OHBF3(OH) + HF

HBF3(OH) + H2OHBF2(OH)2+ HF

HBF2(OH)2+ H2OHBF(OH)3+ HF

HBF(OH)3B(OH)3+ HF

Definitive experimental determination of the hydrolysis of diethyl ether - boron trifluoride according to EC Method C.7 and OECD Test Guideline 111 is 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 concentrations of hydrolysis products. 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 based on these results, the stability of the anticipated degradates, fluoroboric acid (tetrafluoroborate) and boric acid was investigated. With regards to boric acid, the preliminary study showed that at each of pH 1.2, 4, 7 and 9 and 50 ± 0.5 ºC, less than 10 % hydrolysis had occurred after 5 days, equivalent to a half-life of greater than 1 year under environmental conditions (25°C).Boric acid was determined to be hydrolytically stable under acidic, neutral and basic conditions. With regards to tetrafluoroborate, it is apparent that tetrafluoroborate hydrolyses under environmental conditions, forming boric acid and, predominantly, partially hydrolysed fluoroborate species. Wamser reported the reaction rate constant (k) for the hydrolysis of tetrafluoroborate k = 0.00090 min-1 (Wamser, 1948), which corresponds to a half-life of 12.8 hours.