Lithium bis(oxalato)borate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-08-11

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP and guideline compliant study.

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

May 12th 1981

Deviations:

yes

Remarks:

-

Principles of method if other than guideline:

The storage tests could not be carried out in buffer solutions, because all of them contain alkali metal salts. In aqueous solutions of LiBOB and other alkali metal salts a salt metathesis reaction occurs, i.e. precipitates of MBOB-salts (M= Na, K, Rb, Cs) are formed, because such compounds with heavier alkali metals are insoluble in water.

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

not specified

Buffers:

The storage tests could not be carried out in buffer solutions, because all of them contain alkali metal salts. In aqueous solutions of LiBOB and other alkali metal salts a salt metathesis reaction occurs, i.e. precipitates of MBOB-salts (M= Na, K, Rb, Cs) are formed, because such compounds with heavier alkali metals are insoluble in water. For this reason the LiBOB hydrolysis experiments were carried out in heavier alkali element-free solutions.

Details on test conditions:

0.01 m solutions of LiBOB were prepared in heavy water and analyzed with 11B-NMR.

Duration:

1 400 min

Temp.:

25 °C

Initial conc. measured:

>= 8.7 - <= 9.2 other: mmol/kg

Duration:

220 min

Temp.:

40 °C

Initial conc. measured:

>= 7.2 - <= 8.5 other: mmol/kg

Duration:

120 min

pH:

4

Temp.:

60 °C

Initial conc. measured:

ca. 4.4 other: mmol/kg

Duration:

35 min

Temp.:

60 °C

Initial conc. measured:

>= 5.9 - <= 7.6 other: mmol/kg

Number of replicates:

None

Preliminary study:

LiBOB is unstable in water and decomposes into two different products: borole and boric acid. Whereas in concentrated solutions (> ca 0.1 m) a mixture of the borole and boric acid is formed, in dilute solutions only boric acid as decomposition product is observed. In the main study a dilute solution was used.

Transformation products:

no

No.:

#1

% Recovery:

0

pH:

4

Temp.:

25 °C

Duration:

1 400 min

% Recovery:

0

pH:

7

Temp.:

25 °C

Duration:

1 400 min

% Recovery:

0

pH:

9

Temp.:

25 °C

Duration:

1 400 min

% Recovery:

4

pH:

4

Temp.:

40 °C

Duration:

220 min

% Recovery:

4

pH:

7

Temp.:

40 °C

Duration:

220 min

% Recovery:

1.5

pH:

9

Temp.:

40 °C

Duration:

220 min

% Recovery:

0

pH:

4

Temp.:

60 °C

Duration:

120 min

% Recovery:

9.8

pH:

7

Temp.:

60 °C

Duration:

35 min

% Recovery:

11.9

pH:

9

Temp.:

60 °C

Duration:

35 min

pH:

4

Temp.:

25 °C

DT50:

ca. 169 min

St. dev.:

0.991

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

25 °C

DT50:

ca. 182 min

St. dev.:

0.995

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

25 °C

DT50:

ca. 182 min

St. dev.:

0.993

Type:

(pseudo-)first order (= half-life)

pH:

4

Temp.:

40 °C

DT50:

ca. 48 min

St. dev.:

0.998

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

40 °C

DT50:

ca. 48 min

St. dev.:

0.993

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

40 °C

DT50:

ca. 38 min

St. dev.:

0.986

Type:

(pseudo-)first order (= half-life)

pH:

4

Temp.:

60 °C

DT50:

ca. 11 min

St. dev.:

0.973

Type:

(pseudo-)first order (= half-life)

pH:

7

Temp.:

60 °C

DT50:

ca. 12 min

St. dev.:

0.989

Type:

(pseudo-)first order (= half-life)

pH:

9

Temp.:

60 °C

DT50:

ca. 12 min

St. dev.:

0.993

Type:

(pseudo-)first order (= half-life)

Details on results:

With increasing temperatures the hydrolysis of LiBOB is accelerated from 169 min at 25 °C to 12 min at 60 °C. The pH does not seem to have an influence on the hydrolysis reaction.

Validity criteria fulfilled:

not specified

Conclusions:

The hydrolysis of lithium bis(oxalato)borate in different heavier alkali element-free buffer solutions (pH = 4, 7, 9) at different temperatures (T = 25 °C, 40 °C, 60 °C) was investigated using 11B-NMR. Measurements revealed a hydrolysis of LiBOB (half-lives: >12<169 min). The degradation product of the hydrolysis is boric acid (in concentrated solutions borole can also be detected).

Executive summary:

The hydrolysis of lithium bis(oxalato)borate and the identification of the decomposition product were assessed based on the OECD guideline 111 and the EU method C.7. The hydrolysis of lithium bis(oxalato)borate in different heavier alkali element-free buffer solutions (pH = 4, 7, 9) at different temperatures (T = 25°C, 40°C, 60°C) was investigated using 11B-NMR. The half live of LiBOB decreased with increasing temperature. The pH value does not have an influence on the hydrolysis. The detected degradation product boric acid was identified with 11B-NMR.

The storage tests could not be carried out in the recommended buffer solutions as they are all containing alkali metal salts. In aqueous solutions a salt metathesis reaction occurs among the alkali metal salts leading to BOB-salts of heavier alkali metals. These substances are insoluble in water and precipitate. The kinetics of the hydrolysis of heavier alkali metal BOB salts is very different from that of LiBOB. For this reason other buffer solutions had been used in this study. (Chemetall, 2010)

Description of key information

The hydrolysis of lithium bis(oxalato)borate in different heavier alkali element-free buffer solutions (pH = 4, 7, 9) at different temperatures (T = 25°C, 40°C, 60°C) was investigated using 11B-NMR. Measurements revealed a hydrolysis of LiBOB (half-lives: >12<169 min). The degradation product of the hydrolysis is boric acid (in concentrated solutions borole can also be detected). (Chemetall, 2010)
In a study from 2000 of Chemetall more degradation products had been postulated based on mechanistic considerations but were not detected in the study from 2010. Also the half live of about three days could not be confirmed. The new study revealed a much faster degradation.

Key value for chemical safety assessment

Half-life for hydrolysis:

169 min

at the temperature of:

25 °C

Additional information

key study

The hydrolysis of lithium bis(oxalato)borate and the identification of the decomposition product were assessed based on the OECD guideline 111 and the EU method C.7. The hydrolysis of lithium bis(oxalato)borate in different heavier alkali element-free buffer solutions (pH = 4, 7, 9) at different temperatures (T = 25°C, 40°C, 60°C) was investigated using 11B-NMR. The half live of LiBOB decreased with increasing temperature. The pH value instead does not have an influence on the hydrolysis. The detected degradation product boric acid was identified with 11B-NMR. The storage tests could not be carried out in the recommended buffer solutions as they are all containing alkali metal salts. In aqueous solutions a salt metathesis reaction occurs among the alkali metal salts leading to BOB-salts of heavier alkali metals. These substances are insoluble in water and precipitate. The kinetics of the hydrolysis of heavier alkali metal BOB salts is very different from that of LiBOB. For this reason other buffer solutions had been used in this study. (Chemetall, 2010)

other study

Upon contact with water or moisture, lithium bis(oxalato)borate hydrolyses spontaneously. The identity of the degradation products was postulated based on mechanistic considerations. The postulated final degradation products are lithium hydrogen oxalate, oxalic acid, and boric acid. These are responsible for the acidity of the solution (less acid than a comparable solution of oxalic acid which has a pH of 0.9). In organic solvent (e.g. EC/DMC) lithium bis(oxalato)borate hydrolyses if water is added. The postulated degradation products are lithium hydrogen oxalate, the complex C2HBO5, oxalic acid, and boric acid. Lithium hydrogen oxalate and the complex C2HBO5 are poorly soluble and responsible for precipitations. In conclusion of these test results, at a ratio of 1:6 lithium bis(oxalato)borate to water the degradation is estimated to be 50% after about 3 days. (Chemetall, 2000)