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EC number: 274-092-8 | CAS number: 69709-01-9
Hydrolysis
Administrative data
Link to relevant study record(s)
Description of key information
Hydrolysis half-life: 0.7 h at pH 4, <26 h at pH 7 and <0.4 h at pH 9 and 20-25°C (QSAR).
Key value for chemical safety assessment
Additional information
The hydrolysis study is not required at Annex VII. However, hydrolysis is important when considering the interpretation of ecotoxicological tests. Trimethoxysilanes such as 1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine hydrolyse rapidly to moderately rapidly in water to give 1 mole of a trisilanol and 3 moles of methanol.
A QSAR has been developed for the hydrolysis half-lives at pH 4, 7 and 9 of trialkoxysilanes with descriptors for the steric and electronic effects of the side-chain and the steric effects of the alkoxy group.
Using this QSAR, hydrolysis half-lives of 0.7 h at pH 4, 26 h at pH 7 and 0.4 h at pH 9 and 20-25°C were determined for the substance. However, the substance is outside the defined applicability domain of the QSAR in terms of one descriptor value (see QPRF). In addition, the training set does not contain any substances with guanidine side-chains. The QMRF states that substances with a diamine or urea group in the side chain are outside the domain as an intramolecular catalysis mechanism has been identified for these substances. This mechanism results in significantly faster hydrolysis at pH 7 and 9 than would be predicted by the QSAR. It is possible that a substance with a guanidine group could show a similar intramolecular catalysis. Therefore, the predicted half-lives at pH 7 and 9 should be considered as an upper limit of the possible half-lives and the results are therefore reported as <26 h at pH 7 and <0.4 h at pH 9.
This is supported by the results of studies of the acute toxicity of 1,1,3,3-tetramethyl-2-[3-(trimethoxysilyl)propyl]guanidine to Daphnia and algae. The substance was found to hydrolyse very rapidly in test media at pH 8-9.
The hydrolysis products in this case are 1,1,3,3-tetramethyl-2-[3-(trihydroxysilyl)propyl]guanidine (1 mole) and methanol (2 moles).
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