Registration Dossier

Administrative data

Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2006
Report Date:
2006

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 105 (Water Solubility)
Qualifier:
according to
Guideline:
EU Method A.6 (Water Solubility)
GLP compliance:
yes
Type of method:
other: Column elution method chosen for pure water and water buffered at pH 9. Flask method chosen for solubility test at pH 4.

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid: particulate/powder
Specific details on test material used for the study:
Batch-No.: 05.9.9
Expiry date: 20/05/2007
Storage conditions: Dark and dry at ambient temperature.

Results and discussion

Water solubilityopen allclose all
Water solubility:
2.03 mg/L
Conc. based on:
test mat.
Temp.:
20 °C
pH:
7
Remarks on result:
other: Solvent: Pure water (saturated with atmospheric carbon dioxide)
Water solubility:
1.91 mg/L
Conc. based on:
test mat.
Temp.:
30 °C
pH:
7
Remarks on result:
other: Solvent: Pure water (saturated with atmospheric carbon dioxide)
Water solubility:
23.9 mg/L
Conc. based on:
test mat.
Temp.:
20 °C
pH:
4.1
Remarks on result:
other: Solvent: Water, 0.2 mL H2SO4 0.2M
Water solubility:
0.12 mg/L
Conc. based on:
test mat.
Temp.:
20 °C
pH:
9
Remarks on result:
other: Solvent: Borate buffer, 50 mmol/L

Any other information on results incl. tables

Preliminary Test

Table 1: Preliminary test

 Test No.  Test substance weight (g)  Solvent  pH  Determined Copper concentration (mg/L)  Solubility of Cuprous Thiocyanate in Water (mg/L)
 1  2.0005  Pure water  6.95  1.41  2.70
 2  2.0131  Borate buffer, 50 mmol/L  9.01  0.30  0.57
 3  10.0110  50 mL water and 0.2mL H2SO4 (0.2M)  4.05  14.75  28.22

The approximate solubility of the test substance was estimated to be below 0.01 g/L at 20°C in pure water and in water buffered at pH9. For these solvents the column method had to be performed in the main test. The solubility of the test substance was estimated to be above 0.01 g/L for the water/sulphuric acid solution. Therefore the main test has to be performed by the flask method.

Main Test

Column Elution Method

The main test was performed at two different solvent conditions. The results are presented in the following tables.

Solubility in pure water, saturated with atmospheric carbon dioxide

Table 2: pH and copper concentrations during column elution with water, saturated with atmospheric carbon dioxide at 20°C

 Flow  25 mL/h  12.5mL/h
 Fraction  Cu (mg/L)  Cu (mg/L)
 1 1.09   1.04
 2  1.02  1.07
 3  1.04  1.02
 4  1.07  1.10
 5  1.07  1.08
 6  1.07  1.12
 7  1.08  1.01
 8  1.13  0.97
 9  1.06  1.00
 10  1.06  1.07
 Mean  1.07  1.05
 Std. Dev.  0.03  0.05
 RSD in %  2.73  4.56
 Mean of both flows

    1.06

 pH  7.01  6.99

Table 3: pH and Cuprous Thiocyanate concentrations during column elution with water, saturated with atmospheric carbon dioxide at 20°C

 Flow  25 mL/h  12.5mL/h
 Fraction CuSCN CuSCN
 1 2.09 1.99
 2 1.95 2.05
 3 1.99  1.95
 4 2.05  2.10
 5 2.05 2.07 
 6 2.05  2.14
 7  2.07 1.93
 8 2.16 1.86
 9 2.03 1.92
 10 2.03 2.05
 Mean 2.05 2.01
 Std. Dev. 0.06 0.09
 RSD in % 2.74 4.48
 Mean of both flows

   2.03

 pH  7.01 6.99

Table 4: pH and copper concentrations during column elution with water, saturated with atmospheric carbon dioxide at 30°C

 Flow  25 mL/h  12.5mL/h
 Fraction  Cu (mg/L) Cu (mg/L)
 1 0.94 1.06
2 0.92 1.04
 3 0.94 1.03
 4 1.05 1.07
 5 1.06 1.07
 6 0.90 1.12
 7 0.88 1.04
 8 0.89 1.01
 9 0.89 1.04
 10 1.03 1.07
 Mean 0.95 1.06
 Std. Dev. 0.07 0.03
 RSD in % 7.38 2.87
 Mean of both flows

   1.01 

 pH 7.04 7.02

Table 5: pH and Cuprous Thiocyanate concentrations during column elution with water, saturated with atmospheric carbon dioxide at 30°C

 Flow  25 mL/h  12.5mL/h
 Fraction CuSCN CuSCN
 1 1.80 2.03
 2 1.76 1.99
 3 1.80 1.97
 4 2.01 2.05
 5 2.03 2.05
 6 1.72 2.14
 7 1.68 1.99
 8 1.70 1.93
 9 1.70 1.99
 10 1.97 2.05
 Mean 1.79 2.02 
 Std. Dev. 0.13 0.06
 RSD in % 7.17 2.88
 Mean of both flows

1.91 

 pH 7.04 7.02

Solubility in water buffered at pH9

The test fractions were concentrated at final volume that was half of the beginning volume, filtered through 0.45 μm filter, and the dissolved copper was determined.

Table 6: pH and copper concentrations during column elution with water buffered at pH 9 at 20°C

 Flow  25 mL/h  12.5mL/h
 Fraction Cu (mg/L)  Cu (mg/L)
 1 0.06 0.06
 2 0.06 0.06
 3 0.06 0.06
 4 0.06 0.07
 5 0.06 0.07
 6 0.06 0.07
 7 0.06 0.06
 8 0.06 0.07
 9 0.06  0.07
 10 0.06 0.07
 Mean 0.06 0.07
 Std. Dev. 0 0.01
 RSD in % 0 7.82
 Mean of both flows

  0.07

 pH 9.00  9.05

Table 7: pH and Cuprous Thiocyanate concentrations during column elution with water buffered at pH 9 at 20°C

 Flow  25 mL/h  12.5mL/h
 Fraction CuSCN CuSCN
 1 0.11 0.11
 2 0.11 0.11
 3 0.11 0.11
 4 0.11 0.13
 5 0.11 0.13
 6 0.11 0.13
 7 0.11 0.11
 8 0.11 0.13
 9 0.11 0.13
 10 0.11 0.13
 Mean 0.11 0.12
 Std. Dev. 0 0.01
 RSD in % 0 8.47
 Mean of both flows

0.12

 pH 9.00 9.04

Flask Method

The main test was performed at solvent conditions. The results are presented in the following tables.

Solubility in Water/Sulphuric Acid at pH4

Table 8: pH and copper concentrations during solubility test with water/sulphuric acid at pH 4 at 20°C

 Vessel incubation time (h) at 30°C

and re-equilibrium at 20°C

 pH

 Copper Concentration

(mg/L)

 24  4.11  11.65
 48  4.15  12.30
 72  4.13  12.26
 Mean  4.13  12.07
 Std. Dev.  0.02  0.36
 RSD in %  0.5  3.0

Table 9: pH and Cuprous Thiocyanate concentrations during solubility test with water/sulphuric acid at pH 4 at 20°C

 Vessel incubation time (h) at 30°C

and re-equilibrium at 20°C

 pH

 Cuprous Thiocyanate

Concentration (mg/L)

 24  4.11  22.29
 48  4.15  23.54
 72  4.13  23.46
 Mean  4.13  23.09
 Std. Dev.  0.02 0.70
 RSD in %  0.5 3.0

Applicant's summary and conclusion

Conclusions:
The water solubility of cuprous thiocyanate was determined to be:
2.03mg/L in pure water (saturated with atmospheric carbon dioxide) at pH7.0 (20°C); 1.91mg/L in pure water (saturated with atmospheric carbon dioxide) at pH7.0 (30°C); 23.9mg/L in water, 0.2ml H2SO4 0.2M at pH4.1 (20°C); 0.12mg/L in borate buffer, 50mmol/L at pH9.0 (20°C).
Executive summary:

The water solubility of the test substance Cuprous Thiocyanate was determined according to OECD Guideline 105 and EC method A.6. The work was done according to the principles of Good Laboratory Practice.

The solubility of the test substance was determined in pure water, saturated with atmospheric carbon dioxide and in water free of carbon dioxide buffered at pH 9 by the column method. The pH in the neutral range was not adjusted by buffer solution. The pH in the alkaline range was adjusted with a borate buffer solution of 50 mmol/L free of carbon dioxide.

The solubility in the acidic range was determined by the flask method. The solubility in the acidic pH range was determined by titration of 3 g Cuprous Thiocyanate and 200 mL of water with 0.2 M H2SO4 (0.2 mL) until the pH was constant at pH 4.

The solubility tests were performed at 20°C. An additional test was performed with pure water, saturated with atmospheric carbon dioxide at 30°C to show a temperature dependence of the solubility. The temperature dependence was < 3 % per °C.

The samples taken were filtered through 0.45 µm filter.

Temp

(°C)

pH 

Solubility of Cuprous Thiocyanate

in water (mg/L) 

Solvent
20 7.0 2.03

 Pure water

(saturated with atmospheric carbon dioxide)

30 7.0 1.91

 Pure water

(saturated with atmospheric carbon dioxide)

20 4.1 23.9

 Water,

0.2ml H2SO4 0.2M

20 9.0 0.12  Borate buffer, 50 mmol/L

Cuprous Thiocyanate under normal conditions is a mainly covalent solid with a low solubility in water. The dissolution could be explained by the electrolyte theory that assumes all low material to be dissolved, completely dissociated:

CuSCN —> Cu+ + SCN-

This is the basis of the solubility product used in chemical analysis. The Cu+ rapidly gives Cu2+ predominantly.

The solubility of a particular compound depends on the solvating power of the solvent. It also depends on the ionic strength and the pH. At slightly acidic pH, or as acid is added to water containing a trace of Cu ion and thiocyanate ion, in accordance with the Le Chatelier principle, the latter will form thiocyanic acid with the hydrogen ion. This will displace the equilibrium and allow more CuSCN to dissolve. Therefore, what is being measured is not dissolved CuSCN, rather Cu2+ released from the dissociation of the CuSCN molecule.