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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
16 January 2015 to 03 March 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Version / remarks:
2004
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
no
Analytical monitoring:
yes
Buffers:
The buffer systems were selected according to the guidelines. The chosen buffers provided the required pH values. Commercially available solutions were used:
pH 1.2: HCl 0.1 M
pH 4.0: HCl / NaCl / Citric acid
pH 7.0: Na2HPO4 / NaH2PO4
pH 9: H3BO3 / KCl / NaOH
Details on test conditions:
High pH testing (pH 4.0, 7.0 and 9.0)
The test material was used without a co-solvent or a detergent.
1 g (1.3 mMol) of the test material was added to 100 mL of the respective buffer solution in a 250 mL Erlenmeyer flask. The flask was closed with a stopper and heated in a heating cabinet for 5 days (120 h) at 50 °C. The mixture was stirred by a magnetic stirrer using a 40*7, stir bar at approx. 100 rpm. The test was carried out at pH 1.2 and 37 °C.
After the pre-determined reaction time, the reaction mixture was allowed to cool down to room temperature and extracted with hexane. The phases were separated using a separatory funnel. The organic phase was transferred to a pre-weighed flask and the solvent was removed in a rotary evaporator (< 40 °C, 10 mbar). The weight difference was recorded for the mass balance and the samples were analysed by 119Sn-NMR.
The water phase was analysed by AAS for a total tin content.

Gastric pH testing (pH 1.2 / 37 °C)
The test material was used without a co-solvent or a detergent.
1 g (1.3 mMol) test material was added to 100 mL of 0.1 < aqueous solution of hydrochloric acid that was pre-heated to 37 °C in a 250 mL Erlenmeyer flask with ground.
The flask was closed with a stopper and heated on a heating cabinet for 4 h at 37 °C. The mixture was stirred by a magnetic stirrer using a 40 x 7 mm stir bar at approximately 100 rpm.
After the pre-determined exposure time, the solution was allowed to cool down to room temperature; extracted 2 times with 25 mL hexane; the phases were separated using a separatory funnel. The organic phase was transferred into a flask, and the solvent was removed in a rotary evaporator (< 40 °C, 10 mbar). The sample was analysed by 119Sn-NMR spectroscopy.
Duration:
120 h
pH:
4
Temp.:
50 °C
Initial conc. measured:
1.3 mmol/L
Duration:
120 h
pH:
7
Temp.:
50 °C
Initial conc. measured:
1.3 mmol/L
Duration:
120 h
pH:
9
Temp.:
50 °C
Initial conc. measured:
1.3 mmol/L
Duration:
4 h
pH:
1.2
Temp.:
37 °C
Initial conc. measured:
1.3 mmol/L
Remarks:
Gastric pH testing
Number of replicates:
Not specified
Positive controls:
no
Negative controls:
no
Transformation products:
yes
No.:
#1
Details on hydrolysis and appearance of transformation product(s):
Hydrolysis at pH 4.0, 7.0 and 9.0: samples of the test material were added to the respective buffer solutions at 50 °C for 5 days (120 h). The reaction products were extracted with hexane. The 119Sn-NMR spectra of the extracted reaction products did not show any sign of hydrolysis.

Hydrolysis at pH 1.2: A sample of the test material was added to an excess of a 0.1 M hydrochloric acid at 37 °C for 4 h. The 119Sn-NMR spectrum of the recovered reaction product showed that the test material is partially hydrolysed to MMTEC. Both substances were present in equilibrium in a ca. 70/30 MMTE / MMTEC mol % ratio.
MMTEC a product of hydrolysis, has been identified based on the 119Sn-NMR signal at -12.7 ppm. The substance was already present in the non-treated test material as an impurity of ca. 4 % (NMR).
No signal corresponding to MMTC (typically present at 133 ppm) was detected.


pH:
7
Temp.:
50 °C
DT50:
> 1 yr
Type:
not specified
Remarks on result:
other: St. dev. not reported.
Details on results:
Mass balance: For each tested pH value, a 1 g (1.3 mmol) sample of the test material was added to the respective buffer solution. After the required hydrolysis period of 5 days amounts of the hydrolysate were recovered via hexane extraction from the aqueous phase.
The mass balance showed a high recovery of the initial material of the test material after completing the hydrolysis test over the required period (5 days) and the extraction with hexane. It demonstrates high reliability of the chosen experimental design of the study.

The aqueous phases of the hydrolyses at different pH values have been analysed for tin content by AAS.
Tin content in remaining aqueous phases:
pH 4: 280 mg tin/L.
pH 7: 70 mg tin/L.
pH 9: 115 mg tin/L.
This shows that water soluble tin compounds were only present in trace amounts in the reaction mixture after the hydrolysis test followed by the extraction with hexane.

Composition of test material lysate in the pH 1.2 buffer based on 119Sn-NMR analysis

pH value

MMTE

[Mol%]

MMTEC

[Mol%]

MMTE:MMTCE ratio

Start

96

4

96:4

pH 1.2

69

31

69:31

NMR ppm

6807

-12.7

 

 

Recovery of the tested material

pH

Initial mass

[g]

Recovered

[g]

Recovery rate

[%]

4

1.0

0.89

89

7

1.0

0.97

97

9

1.0

0.89

89

 

Validity criteria fulfilled:
not specified
Conclusions:
Under the conditions of the study the test material at pH 4, 7 and 9 can be considered hydrolytically stable. After 5 days at 50 °C less than 10 % of the test material was hydrolysed (t0.5 25°C > 1 year).
Under simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) the test material was partially hydrolysed to its monochloro ester.
It can be concluded that the monochloro ester is the only metabolite of the test material that was formed in the simulated mammalian gastric environment. 
Executive summary:

The hydrolysis of the test material was assessed according to OECD Test Guideline 111 and EU Method C.7. Quantitative ^119Sn-NMR spectroscopy has been used as a valuable analytical tool to directly identify and quantify all organotin components, which are formed as a result of hydrolysis of the tested substance.

The study shows that the test material at pH 4, 7 and 9 can be considered hydrolytically stable. After 5 days at 50 °C less than 10 % of the test material was hydrolysed (t0.5 25°C > 1 year).

Under the simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) the test material was partially hydrolysed to its monochloro ester.

It can be concluded that the monochloro ester is the only metabolite of the test material that was formed in the simulated mammalian gastric environment. No MMTC was formed under the conditions of the study.

Description of key information

Under the conditions of the study the test material at pH 4, 7 and 9 can be considered hydrolytically stable. After 5 days at 50 °C less than 10 % of the test material was hydrolysed (t0.5 25°C > 1 year).

Under simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) the test material was partially hydrolysed to its monochloro ester.

It can be concluded that the monochloro ester is the only metabolite of the test material that was formed in the simulated mammalian gastric environment. 

Key value for chemical safety assessment

Additional information

The hydrolysis of the test material was assessed according to OECD Test Guideline 111 and EU Method C.7. Quantitative ^119Sn-NMR spectroscopy has been used as a valuable analytical tool to directly identify and quantify all organotin components, which are formed as a result of hydrolysis of the tested substance.

The study shows that the test material at pH 4, 7 and 9 can be considered hydrolytically stable. After 5 days at 50 °C less than 10 % of the test material was hydrolysed (t0.5 25°C > 1 year).

Under the simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) the test material was partially hydrolysed to its monochloro ester.

It can be concluded that the monochloro ester is the only metabolite of the test material that was formed in the simulated mammalian gastric environment. No MMTC was formed under the conditions of the study.