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Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
28 November - 07 December 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 105 (Water Solubility)
Version / remarks:
adopted 27th July 1995
Deviations:
yes
Remarks:
see principles of method if other than guideline
Qualifier:
according to guideline
Guideline:
EU Method A.6 (Water Solubility)
Version / remarks:
(EC) No 440/2008
Deviations:
yes
Remarks:
see principles of method if other than guideline
Principles of method if other than guideline:
In the definitive test, the temperature in the equilibration phase ranged from 20.4 to 21.1°C, with a mean of 20.7°C and was thus out of the range of 20 ± 0.5°C. However, this effect should be negligible considering a typical statistical uncertainty of at least 5 to 10% for such experimentally derived results due to the sampling process as well as substance-specific analysis.
GLP compliance:
yes (incl. QA statement)
Type of method:
flask method
Specific details on test material used for the study:
Batch No: CNAA053604
Storage: At room temperature, ca. 20°C
Key result
Water solubility:
75.4 mg/L
Conc. based on:
test mat. (dissolved fraction)
Temp.:
20 °C
pH:
>= 5.3 - <= 6.7
Remarks on result:
other: water solubility of N-propylphthalimide
Key result
Water solubility:
97.8 mg/L
Conc. based on:
test mat. (dissolved fraction)
Temp.:
20 °C
pH:
>= 5.3 - <= 6.7
Remarks on result:
other: water solubility of N-sec-butyl-phthalimide
Key result
Water solubility:
157 mg/L
Conc. based on:
test mat. (dissolved fraction)
Temp.:
20 °C
pH:
>= 5.3 - <= 6.7
Remarks on result:
other: water solubility of N-butylphthalimide
Details on results:
Preliminary test
The content of test item dissolved in the water sample was <1 g/L.

Main test
The test results obtained for all three, main components of the test item after one, two and seven days of stirring at 30 °C demonstrated that saturation had already been reached after one day of stirring. Due to significantly higher concentrations, test vessel three was considered an outlier and not used for further evaluation.
The water solubilities of the three, main components of the test item, calculated as the mean of test vessels one, two and four, are 75.4 mg/L for N-propylphthalimide, 97.8 mg/L for N-sec-butyl-phthalimide and 157 mg/L for N-butylphthalimide at pH values of 5.3 to 6.7 and ca. 20 °C. The test is satisfactory, if the concentrations of the three vessels do not differ by more than 15%. Detailed results are given in the table in the next section.

HPLC determinations for N-propylphthalimide:

 Test vessel  pH  Analysed concentration A (mg/L)   Analysed concentration B (mg/L)   Analysed concentration C (mg/L)   Mean (g/L)
 No. 1  6.6  67.3 77.1  74.1   72.8
 No. 2  6.7  74.8 75.2  75.2   75.1
 No. 4  5.3  79.2 77.2  78.7   78.4
      Overall Mean  75.4

The concentrations of the three vessels differed by 7% (validity criterion given by OECD is met).

HPLC determinations for N-sec-butyl-phthalimide:

 Test vessel  pH  Analysed concentration A (mg/L)   Analysed concentration B (mg/L)   Analysed concentration C (mg/L)   Mean (g/L)
 No. 1  6.6  90.8  108  99.4  99.4
 No. 2  6.7  95.2  96.3  95.6  95.7
 No. 4  5.3  100  96.6  98.2  98.3
         Overall Mean  97.8

The concentrations of the three vessels differed by 4% (validity criterion given by OECD is met).

HPLC determinations for N-butylphthalimide:

 Test vessel  pH  Analysed concentration A (mg/L)   Analysed concentration B (mg/L)   Analysed concentration C (mg/L)   Mean (g/L)
 No. 1  6.6  143  175  159  159
 No. 2  6.7  153  153  154  153
 No. 4  5.3  162  156  159  159
          Overall Mean  157

The concentrations of the three vessels differed by 4% (validity criterion given by OECD is met).

Further remarks

Using the SMILES code (section 4.2), the water solubilities of the three, main components of the test item were estimated to be 370 mg/l for N-propylphthalimide, 138 mg/l for N-secbutylphthalimide and 120 mg/l for N-butylphthalimide (WSKOW v1.42, EPI Suite v4.11). The experimentally obtained results in this study are in the same order of magnitude for N-secbutylphthalimide and N-butylphthalimide, however, they are significantly lower for Npropylphthalimide. The reason for this discrepancy is most likely due to the low content of only 13.5% N-propylphthalimide in the test item corresponding to 135 mg/l per test vessel (instead of 1850 mg/l N-propylphthalimide, which is the theoretical, initial loading for an OECD 105 test considering an intended fivefold excess of substance in the test vessel by the guideline). Furthermore, the three test item components with varying contents in the test item were not separately dissolved in water but together, which most probably led to competitive effects, especially considering the structural similarities of the three, main components of the test item.

Conclusions:
The water solubilities of the three, main components of the test item “Reaction mass of N-butylphthalimide and N-propylphthalimide and N-sec-butylphthalimide” were determined according to TG OECD 105 and revealed 75.4 mg/L for N-propylphthalimide, 97.8 mg/L for N-sec-butyl-phthalimide and 157 mg/L for N-butylphthalimide at pH values of 5.3 to 6.7 and ca. 20 °C.
Executive summary:

The water solubilities of the three, main components of the test item “Reaction mass of N-butylphthalimide and N-propylphthalimide and N-sec-butylphthalimide” were determined according to TG OECD 105.

Several test vessels containing ultra-pure water mixed with test item in great excess (initial amount of test item about 1 g per liter water), were incubated and stirred for different periods of time at about 30 °C (saturation phase), and then transferred to about 20 °C for 24 h (equilibration phase). Samples were taken from the middle of the solution by syringe, as undissolved test item swam on the surface of the test solution. The concentrations of the three main components of the test item in the clear aqueous phase were determined by HPLC.

Since the results after one, two and three days showed increasing concentrations, the test was prolonged by using longer equilibration times, and the concentrations were also determined after seven days.

No significant variation of the concentrations in the three respective test vessels was observed after one, two and seven days of incubation at 30 °C (followed by 24 h equilibration at ca. 20 °C). Due to significantly higher concentrations, test vessel three, which was incubated at 30 °C for three days and then equilibrated at ca. 20 °C for 24 h, was considered an outlier and not used for further evaluation.

The water solubilities of the three, main components of the test item, calculated as the mean of test vessels one, two and four, are 75.4 mg/L for N-propylphthalimide, 97.8 mg/L for N-sec-butyl-phthalimide and 157 mg/L for N-butylphthalimide at pH values of 5.3 to 6.7 and ca. 20 °C.

The validity criterion was fulfilled.

Description of key information

The water solubilities of the three, main components of Reaction mass of N-butylphthalimide and N-propylphthalimide and N-sec-butylphthalimide have been determined in a GLP study according to OECD guideline 105.

Results per component (mean of three test vessels): 75.4 mg/l for N-propylphthalimide, 97.8 mg/l for N-sec-butylphthalimide and 157 mg/l for N-butylphthalimide at pH values of 5.3 to 6.7 and ca. 20 °C (Klimisch 1, ACH 2017).

Key value for chemical safety assessment

Water solubility:
157 mg/L
at the temperature of:
20 °C

Additional information

The substance consists of three components. The value of the component with the highest water solubility has been used as key value as a worst-case.

Results per component (mean of three test vessels):

N-butylphthalimide (CAS No 1515-72-6):              157 mg/l

N-sec-butylphthalimide (CAS No 10108-61-9):       97.8 mg/l

N-propylphthalimide (CAS No5323-50-2):              75.4 mg/l