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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
06.07.2016-11.01.2017
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
OECD Guideline 111 (Hydrolysis as a Function of pH)
Deviations:
yes
Remarks:
The test item has been used as neat material, not as solution
GLP compliance:
no
Remarks:
Inhouse study
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
1 g (1.18 mMol) test item 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 hours) at 50°C.
The mixture was stirred by a magnetic stirrer using a 40*7 mm stir bar at approx. 100 rpm.
The test at pH 1.2 was carried out at 37 °C
Each reaction mixture was extracted with 20 ml hexane, the phases were separated using a separatory funnel. The organic phase was transferred into 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 analyzed by 119Sn-NMR
The aqueous phases were analysed by AAS for tin content.
Buffers:
Commercially available solutions purchased from VWR International GmbH
pH 1.2 HCl 0.1 M
pH 4.0 HCl/NaCl/Citric acid
pH 7.0 Na2HPO4/NaH2PO4
pH 9.0 H3BO3/KCl/NaOH
Details on test conditions:
Performing Tier 1 testing:

Tier 1 Testing (pH 1.2, 4.0, 7.0, 9.0):
1 g (1.18 mMol) test item 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 hours) at 50°C. The mixture was stirred by a magnetic stirrer using a 40*7 mm 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 solution was allowed to cool down to room temperature; each reaction mixture was extracted with 20 ml hexane, the phases were separated using a separatory funnel. The organic phase was transferred into 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 analyzed by 119Sn-NMR.

Tier 2 Testing (pH 1.2/37°C)
1 g (1.3 mMol) Test Item was added to 100 ml of 0.1 M hydrochloric acid that was preheated to 37 °C in an 250 ml Erlenmeyer flask with ground. For the initial time of the experiment (15 seconds), the reaction products were extracted with hexane immediately according to the below-described procedure. For longer exposure/hydrolysis times, the flask was closed with a stopper and heated in a heating cabinet for 1, 2, 4, 8, 24, and 48 hours at 37°C. The mixture was stirred by a magnetic stirrer using a 40*7 mm stir bar at approx. 100 rpm.

After the pre-determined reaction time, the solution was allowed to cool down to room temperature; each reaction mixture was extracted with 20 ml hexane; the phases were separated using a separatory funnel. The organic phase was transferred into 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 analyzed by 119Sn-NMR.

The experiments were run in duplicate.

Duration:
120 h
pH:
4
Temp.:
50 °C
Duration:
120 h
pH:
7
Temp.:
50 °C
Duration:
120 h
pH:
9
Temp.:
50 °C
Duration:
120 h
pH:
1.2
Temp.:
37 °C
Duration:
0.004 h
pH:
1.2
Temp.:
37 °C
Number of replicates:
The test at pH 1.2 have been run in duplicate for 0.004/1/2/4/8/24/48 hours
Transformation products:
yes
No.:
#1
Details on hydrolysis and appearance of transformation product(s):
Transformation product of the hydrolysis at low pH is Monooctyltin chloro bis(2-ethylhexylmercaptoacetate)
At pH 4 and 7 the substance was considered hyrolytically stable
At pH 9 the 39 % of the unreated substance coud be extracted with hexane from the reaction mixture. 61 % degraded into a more water soluble species which could not be unequivocally characterised. It is most likely a hydroxide.
pH:
4
Temp.:
25 °C
DT50:
> 1 yr
pH:
7
Temp.:
25 °C
DT50:
> 1 yr
pH:
9
Temp.:
25 °C
DT50:
< 1 yr
pH:
1.2
Temp.:
37 °C
DT50:
< 1 min
Validity criteria fulfilled:
yes
Conclusions:
The study showed that MOTE at pH 7 and 4 can be considered hydrolytically stable. After 5 days at 50 °C less than 10% DOTE was hydrolyzed (t 0.5 25°C > 1 year).
At pH 9 the 39 % of the unreated substance coud be extracted with hexane from the reaction mixture. 61 % degraded into a more water soluble species which could not be unequivocally characterised. It is most likely a hydroxide
Under the simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) MOTE was hydrolyzed to (Monooctyltin chloro bis(2-ethylhexyl mercaptoacetate) (MOTCE2), its monochloro ester.
It can be concluded that MOTCE2 is the only metabolite of MOTE that was formed in the simulated mammalian gastric environment. No Dichloro etster (MOTC2E) or MOTC was formed under the conditions of this study.
Executive summary:

The study showed that MOTE at pH 7 and 4 can be considered hydrolytically stable.  After 5 days at 50 °C less than 10% DOTE was hydrolyzed (t 0.5 25°C > 1 year).

At pH 9 the 39 % of the unreated substance coud be extracted with hexane from the reaction mixture. 61 % degraded into a more water soluble species which could not be unequivocally characterised. It is most likely a hydroxide

Under the simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) MOTE was hydrolyzed to (Monooctyltin chloro bis(2-ethylhexyl mercaptoacetate) (MOTCE2), its monochloro ester.

It can be concluded that MOTCE2 is the only metabolite of MOTE that was formed in the simulated mammalian gastric environment. No Dichloro etster (MOTC2E) or  MOTC was formed under the conditions of this study.

Description of key information

The study showed that MOTE at pH 7 and 4 can be considered hydrolytically stable.  After 5 days at 50 °C less than 10% DOTE was hydrolyzed (t 0.5 25°C > 1 year).

At pH 9 the 39 % of the unreated substance coud be extracted with hexane from the reaction mixture. 61 % degraded into a more water soluble species which could not be unequivocally characterised. It is most likely a hydroxide

Under the simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) MOTE was hydrolyzed to (Monooctyltin chloro bis(2-ethylhexyl mercaptoacetate) (MOTCE2), its monochloro ester.

It can be concluded that MOTCE2 is the only metabolite of MOTE that was formed in the simulated mammalian gastric environment. No Dichloro etster (MOTC2E) or  MOTC was formed under the conditions of this study.

Key value for chemical safety assessment

Additional information

The study showed that MOTE at pH 7 and 4 can be considered hydrolytically stable.  After 5 days at 50 °C less than 10% DOTE was hydrolyzed (t 0.5 25°C > 1 year).

At pH 9 the 39 % of the unreated substance coud be extracted with hexane from the reaction mixture. 61 % degraded into a more water soluble species which could not be unequivocally characterised. It is most likely a hydroxide

Under the simulated gastric conditions (0.1 M HCl / pH 1.2 / 37 °C) MOTE was hydrolyzed to (Monooctyltin chloro bis(2-ethylhexyl mercaptoacetate) (MOTCE2), its monochloro ester.

It can be concluded that MOTCE2 is the only metabolite of MOTE that was formed in the simulated mammalian gastric environment. No Dichloro etster (MOTC2E) or  MOTC was formed under the conditions of this study.