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Hydrolysis

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Reference
Endpoint:
hydrolysis
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2016-08-11
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods
Justification for type of information:
QSAR calculation was performed as supporting information. HYDROWIN gave the following prediction regarding hydrolysis based on the chemical structure of the test item:

"Isocyanates hydrolyze readily in water to yield a carbamic acid, which decarboxylates to produce CO2 and an amine; the latter immediately reacts with more isocyanate to yield a disubstituted urea. The hydrolysis rate increases with electron-withdrawing substituents. Steric hindrance also influences hydrolysis rate; aliphatic isocyanate rates are:
primary > secondary > tertiary (Ullmann's Encycl, A14:611-613). Even at low pHs, hydrolysis Half-Life < 10 minutes (25 deg C) Experimental Hydrolysis Half-Lifes (HSDB, 2007):
Methyl isocyanate: 9 minutes (25 deg C)
Phenyl isocyanate: 55 seconds (water/dioxane solution)

Hydrolysis of alkoxysilanes is both acid and base-catalyzed (Osterholtz and Pohl, 1992; Mill and Tse, 1989). Rates are slowest near pH7."

Once the Isocyanate group is hydrolyzed, the resulting structures are predicted to be hydrolytically stable or having hydrolytical half lifes of > 100 days.
Qualifier:
no guideline followed
Principles of method if other than guideline:
The substance solubility and degradation in water was analytically investigated.
GLP compliance:
yes
Remarks:
In house data according to GLP-like accepted national standards.
Specific details on test material used for the study:
SMILES: CO[Si](CCCSC(=O)NCCCCCCNC(=O)N(CCCCCC\N=C=O)C(=O)NCCCCCCC\N=C=O)(OC)OC
Radiolabelling:
no
Analytical monitoring:
yes
Details on sampling:
- Sampling intervals for the parent/transformation products: Three and fifteen days after preparation of the aqueous suspension a mass spectrum was recorded

- Other observation, if any: initially an aqueous suspension in water was observed. Gradually the suspension became clear within 5-7 days while a white solid matter was formed at the bottom and the wall of the glass vial.
Number of replicates:
3
Positive controls:
no
Negative controls:
no
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
Key result
Remarks on result:
not determinable because of methodological limitations

The vortex-shaked aqueous solutions of the test item were initially cloudy. Two milliliters of each solution were filtered through a 0.2 μm PTFE-membrane. As a result clear aqueous solutions were obtained. Consequently the test item forms an aqueous suspension in water. Gradually the suspensions became clear within 5-7 days while a white solid matter was formed at the bottom and the wall of the glass vial. Three days after preparation of the aqueous suspension a mass spectrum was recorded.

Basically hydrolyzed Hexamethylene diisocyanate, oligomers (-2CO2) and adducts with Mercaptopropyltrimethoxysilane(- MeOH) were found in the clear aqueous solution. The measurement was repeated after 15 days. The mass spectra indicate no significant difference.

The mass spectrum of the test item sample shows a signal at m/z = 427.33740. Based on the accurate mass measured, the chemical formula of C21H42O3N6 and 4 ring double bond equivalents (RDB) were calculated for the neutral molecule.

The mass spectrum of the test item shows a signal at m/z = 581.34979. Based on the accurate mass measured, the chemical formula of C24H52O6N6SSi and 3 ring double bond equivalents (RDB) were calculated for the neutral molecule. The mass spectrum of the test item sample shows a signal at m/z = 629.31067. Based on the accurate mass measured, the chemical formula of C25H50O7N6NaSSi+ and 5 ring double bond equivalents (RDB) were calculated for the neutral molecule. The mass spectrum of the test item sample shows a signal at m/z = 761.34100. Based on the accurate mass measured, the chemical formula of C28H60O10N6S2Si2 + and 4 ring double bond equivalents (RDB) were calculated for the neutral molecule.

Executive summary:

The test item is a reaction product of Hexamethylene diisocyanate, oligomers with Mercaptopropyltrimethoxysilane. The sample was tested in water for environmental behavior. Therefore, it is essential to know whether the sample will react in presence of water to polymeric components. The test item formed initially an aqueous suspension in water. Gradually the suspension became clear within 5-7 days while a white solid matter was formed at the bottom and the wall of the glass vial. Three days after preparation of the aqueous suspension a mass spectrum was recorded. Basically hydrolyzed Hexamethylene diisocyanate, oligomers (-2CO2) and adducts with Mercaptopropyltrimethoxysilane (- MeOH) were found in the clear aqueous solution. The measurement was repeated after 15 days. The mass spectra indicate no significant difference.

Description of key information

The study cannot be conducted due to technical limitations. Based on company data the substance hydrolses rapidly. This is further supported by QSAR calculation.

Key value for chemical safety assessment

Additional information

The substance is not stable in water. Its technical function is to hydrolyse and/or polymerize rapidly upon contact with water. Thus, it was technically not feasible to develop and validate analytical method suitable to detect the substance or its hydrolysis products in water. Consequently, it is technically not feasible to conduct the study according to OECD 111 under GLP.

The test item is a reaction product of Hexamethylene diisocyanate, oligomers with Mercaptopropyltrimethoxysilane. The sample was tested in water to determine its environmental behavior as it is essential to know whether the sample will react in presence of water to polymeric components. The test item formed initially an aqueous suspension in water. Gradually the suspension became clear within 5 - 7 days while a white solid matter was formed at the bottom and the wall of the glass vial. Three days after preparation of the aqueous suspension a mass spectrum was recorded. Basically hydrolyzed Hexamethylene diisocyanate, oligomers (-2CO2) and adducts with Mercaptopropyltrimethoxysilane(- MeOH) were found in the clear aqueous solution. The measurement was repeated after 15 days. The mass spectra indicate no significant difference.

Alongside the expected polymer fractions in the water phase were detected the theoretical hydrolysis products - (3-mercaptopropyl)trimethoxysilane (MPTMS) and Methanol. According to published data (ECHA Disseminated Database) both hydrolysis products are also not hydrolytically stable. An identification of these hydrolysis products was possible only by the molecular weight in the mass spectrum. Determination using reference substances as external standard was also not possible due to their hydrolytical instability.

 

Additionally, a QSAR estimation using Hydrowin (v.2.0 , part of EpiSuite v.4.11) was performed and a half-life of <10 min at 25 °C for the test item was estimated.

The adequacy of a prediction depends on the following conditions:

a) the (Q)SAR model is scientifically valid: the scientific validity is established according to the OECD principles for (Q)SAR validation;

b) the (Q)SAR model is applicable to the query chemical: a (Q)SAR is applicable if the query chemical falls within the defined applicability domain of the model;

c) the (Q)SAR result is reliable: a valid (Q)SAR that is applied to a chemical falling within its applicability domain provides a reliable result;

d) the (Q)SAR model is relevant for the regulatory purpose.

 

For assessment and justification of these 4 requirements the QMRF and QPRF files were developed and attached to this study record.

 

Description of the prediction Model

The prediction model was descripted using the harmonised template for summarising and reporting key information on (Q)SAR models. For more details please refer to the attached QSAR Model Reporting Format (QMRF) file. 

 

Assessment of estimation domain

The assessment of the estimation domain was documented in the QSAR Prediction Reporting Format file (QPRF). Please refer to the attached document for the details of the prediction and the assessment of the estimation domain.