Lithium hexafluorophosphate(1-)

Dissociation constant

Administrative data

Endpoint:

dissociation constant

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is hydrolytically unstable (half-life less than 12 hours)

Cross-reference

Reason / purpose for cross-reference:

data waiving: supporting information

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Adequately documented investigation of hydrolysis rate in contact with water and atmospheric moisture, using non-standard methodology which is however suitable for the particular properties of the test substance.

Principles of method if other than guideline:

[1] Observation of speed of dissolution and hydrolysis in water by measurement of HF formation by pH determination and LiF formation by pF determination.
[2] Observation of reaction with atmospheric moisture by accurate monitoring of sample weight change.

GLP compliance:

not specified

Remarks:

This study was a bespoke test performed by the manufacturer of the substance. This study was not carried out specifically for REACH, however it provides key information to show the substance is hydrolytically unstable and relevant for risk assessment.

Analytical monitoring:

yes

Details on test conditions:

Hydrolysis on contact with water.
Experiment 1:
5g samples of test material added to 500 ml volumes of water with stirring - test run with water at 20, 30, 40, 50 and 60C. pH and pF recorded at start (T0) and when reaction appeared complete, as judged by pH/pF change (15-21 seconds after sample addition).
Experiment2:
different amounts of test substance (5-50g) added to 500 ml volumes of water with stirring, at 20C. pH and pF recorded at start (T0) and when reaction appeared complete, as judged by pH/pF change (21-49 seconds after sample addition).
Experiment 3:
30g samples of test material added to 500 ml volumes of water with stirring - test run with water at 20, 30, 40, 50 and 60C. pH and pF recorded at start (T0) and at intervals until the reaction appeared complete, as judged by pH/pF change (11-42 seconds after sample addition).

Reaction with atmospheric moisture.
Experiment 1:
approximately 1g samples of test material (accurately weighed to 0.1 mg) exposed to high humidity atmospheres (84.4-93.6% RH) for up to 150 minutes, with accurate recording of sample mass at frequent intervals. Separate determinations for two test samples showing some difference in particle size (designated big and small).
Experiment 2:
3 further determinations of sample mass change in moist air of differing RH (54.7-85.8%), over time periods up to 160 minutes and using the test material designated small particle size.

Number of replicates:

Hydrolysis in contact with water: 3 experiments, 5 different test temperatures.
Reaction with atmospheric moisture: 2 experiments, different RH levels and sample particulate sizes.

Statistical methods:

Not applicable

Transformation products:

yes

No.:

#1

No.:

#2

No.:

#3

Details on hydrolysis and appearance of transformation product(s):

It was known that the test substance reacts rapidly with water, releasing HF/hydrofluoric acid, LiF and phosphoric acid. The hydrolysis reaction was followed by measurement of pH and PF.
Reaction with atmospheric moisture was shown to follow a biphasic pattern: an initial increase considered to reflect water absorption was followed by a decrease associated with release of POF3 and HF.

DT50:

< 3 s

Type:

not specified

Remarks on result:

other: hydrolysis rate constant not determined

Reaction with water: Experiment 1

Sample number	Temperature[C]	Sample weight	pH Start	pH End	pF Start	pF End	End time (secs)
1	20	5.06	6.35	4.32	7.05	4.46	20
2	30	5.03	6.52	4.57	8.51	4.91	15
3	40	5.05	6.02	4.66	7.03	4.84	20
4	50	5.04	5.87	4.65	6.63	4.91	20
5	60	5.02	6.00	4.60	7.20	5.05	21

Reaction with water: Experiment 2

Sample number	Temperature[C]	Sample weight	pH Start	pH End	pF Start	pF End	End time (secs)
1	20	5	6.00	4.60	7.20	5.05	21
2	20	20	7.45	3.17	7.18	3.18	31
3	20	30	6.23	3.52	7.23	3.71	42
4	20	40	6.43	3.06	7.32	3.31	49
5	20	50	6.25	3.08	7.12	3.48	32

Reaction with water: Experiment 3 (summarised)

Sample number	Temperature[C]	Sample weight	pH Start	pH End	pF Start	pF End	End time (secs)
1	20	30	6.23	3.52	7.23	3.71	42
2	30	30	6.53	3.32	7.68	3.74	22
3	40	30	5.70	3.53	6.76	3.96	16
4	50	30	5.39	2.70	6.18	3.37	29
5	60	30	5.70	1.75	6.06	3.05	11

Reaction with water: Experiment 3 (full results)

Temperature 20 C sample 30g			Temperature 30 C sample 30g			Temperature 40 C sample 30g
Time (secs)	pH	pF	time	pH	pF	time	pH	pF
0	6.23	7.23	0	6.53	7.68	0	5.70	6.76
3	3.55	3.75	3	3.35	3.77	3	3.56	3.99
5	3.55	3.74	5	3.34	3.76	5	3.55	3.98
10	3.54	3.73	10	3.33	3.75	10	3.54	3.97
20	3.53	3.73	22	3.32	3.74	16	3.53	3.96
30	3.53	3.72	-	-	-	-	-	-
42	3.52	3.71	-	-	-	-	-	-
Temperature 50 C sample 30g			Temperature 60 C sample 30g
Time (secs)	pH	pF	time	pH	pF
0	5.39	6.18	0	5.70	6.06
3	2.75	3.40	3	1.77	3.07
5	2.74	3.39	5	1.76	3.06
10	2.73	3.38	11	1.75	3.05

Moist air reaction, Experiment 1: LPF big particle, 19.6 C, humidity 93.6%

Time [min]	Mass [g]	Time [min]	Mass [g]	Time [min]	Mass [g]
0	1.0438	60	1.0502	110	1.0761
10	1.0547	70	1.0540	120	1.0802
20	1.0596	80	1.0583	130	1.0864
30	1.0545	90	1.0641	140	1.0902
40	1.0520	100	1.0699	150	1.0974
50	1.0491	-	-	-	-

Mass increase: (1.0596-1.0438) /1.0438=1.5% time: 20min. Mass decrease: (1.0596-1.0491) /1.0596=0.99% time: 30min.

Moist air reaction, Experiment 1: LPF small particle, 20.7 C, humidity 84.4%

Time [min]	Mass [g]	Time [min]	Mass [g]	Time [min]	Mass [g]
0	1.0049	30	1.0071	60	0.9970
5	1.0095	35	1.0039	65	0.9977
10	1.0133	40	1.0008	70	0.9987
15	1.0137	45	0.9988	75	0.9998
20	1.0125	50	0.9977	80	1.0010
25	1.0097	55	0.9973	85	1.0025

Mass increase: (1.0137-1.0049) /1.0049=0.87% time: 15min. Mass decrease: (1.0137-0.9970) /1.0137=1.65% time: 45min.

Moist air reaction, Experiment 2: LPF small particle, 20.7 C, humidity 85.8%

Time [min]	Mass [g]	Time [min]	Mass [g]	Time [min]	Mass [g]
0	1.0462	25	1.0456	50	1.0468
5	1.0491	30	1.0444	55	1.0482
10	1.0520	35	1.0438	60	1.0497
15	1.0496	40	1.0441	65	1.0511
20	1.0478	45	1.0451	70	1.0524

Mass increase: (1.0520-1.0462) /1.0462=0.55% time: 10min. mass decrease: (1.0520-1.0438) /1.0520=0.78% time: 25min.

Moist air reaction, Experiment 2: LPF small particle, 20.4 C, humidity 65.1%

Time [min]	Mass [g]	Time [min]	Mass [g]	Time [min]	Mass [g]
0	1.0201	35	1.0031	70	0.9991
5	1.0235	40	1.0008	75	1.0002
10	1.0238	45	0.9992	80	1.0008
15	1.0201	50	0.9992	85	1.0010
20	1.0155	55	0.9990	90	1.0028
25	1.0113	60	0.9988	95	1.0037
30	1.0070	65	0.9987	100	1.0047

Mass increase: (1.0238-1.0201) /1.0201=0.36% time: 10min. Mass decrease: (1.0238-0.9987) /1.0238=0.25% time: 55min.

Moist air reaction, Experiment 2: LPF small particle, 21.5 C, humidity 54.7%

Time [min]	Mass [g]	Time [min]	Mass [g]	Time [min]	Mass [g]
0	1.0567	55	1.0194	110	1.0073
5	1.0585	60	1.0177	115	1.0070
10	1.0596	65	1.0159	120	1.0064
15	1.0599	70	1.0143	125	1.0054
20	1.0571	75	1.0119	130	1.0060
25	1.0533	80	1.0110	135	1.0058
30	1.0479	85	1.0114	140	1.0057
35	1.0440	90	1.0101	145	1.0056
40	1.0381	95	1.0097	150	1.0065
45	1.0265	100	1.0092	155	1.0080
50	1.0226	105	1.0074	160	1.0088

Mass decrease: (1.0599-1.0567) /1.0567=0.30% time: 15min. Mass decrease: (1.0599-1.0056) /1.0599=5.12% time: 130min.

Conclusions:

Rapid reaction with water releases HF and LiF, leading to production of dissolved F- ions; subsequently, release of Li+ and PO4(3-) ions will follow.