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EC number: 221-338-7 | CAS number: 3069-40-7
Test Conditions (de-ionized water):
When preparing the test solution (100 mg/l), the substance was observed to react rapidly with water with the generation of HCl and a flocculent white precipitate. After stirring for 4 hours and heating to 60°C the precipitate did not disappear. Before measurement at 20°C the precipitate was removed by filtration.
The concentration of the test substance was determined using the method for total carbon in the solution according to DIN EN 1484 H3. No carbon could be detected (detection limit < 3 mg/l). Additionally a 1H-NMR spectrum was measured. There was no signal of CH2Si or CH2 groups of an octyl chain. Therefore there is no indication of the test substance or organic groups as products of hydrolysis in the aqueous solution (detection limit < 10 mg/l).
Due to the very low concentration of dissolved material, it is difficult to interpret the result of the study.
The test substance was expected to hydrolyse rapidly generating HCl which will lower the pH of the solution. The condensation reaction of the silanol hydrolysis product are expected to be promoted at lower pH. Therefore the study was repeated in a pH 7 buffer solution as test medium.
Table 1: Surface tension result for non-neutralised (non-buffered solution)
Time after transferring to the measurement vessel [min]
Total mean value
Mean value (state of equilibrium)
Test Conditions (pH 7 buffer solution):
When preparing the test solution (100 mg/l) with the buffer solution at pH 7, the substance was observed to react at rapidly with water with flocculent white precipitate being generated. After 3 days the precipitate did not disappear. Before measurement at 20°C the precipitate was removed by filtration.
A 1H-NMR spectrum of the test solution was measured. There was no signal of CH2Si or CH2 groups of an octyl chain. Therefore there is no indication of the test substance or organic groups as products of hydrolysis in the aqueous solution (detection limit < 10 mg/l).
It was assumed that a very small amount of the hydrolysis product of the test substance remained on the surface of the aqueous solution. This was considered a possible reason for the effect of surface tension.
Table 2: Surface tension result for neutralised (buffered solution)
Surface tension [trimethoxy(octyl)silane]: not relevant due to rapid hydrolysis in contact with water
Surface tension [octylsilanetriol]: 53 mN/m (EU Method A.5)
The surface tension study for trimethoxy(octyl)silane (CAS 3069-40-7) was waived because in contact with water, the registered substance hydrolyse rapidly to form octylsilanetriol and methanol. The surface tension of the silanol hydrolysis product, octylsilanetriol was read-across from related substance; octyltrichlorosilane (CAS 5283-66-9).
In contact with water, trimethoxy(octyl)silane will hydrolyse rapidly to form octylsilanetriol and methanol. Similarly, octyltrichlorosilane will hydrolyse very rapidly in contact with water to form octylsilanetriol and hydrochloric acid. Both substances (trimethoxy(octyl)silane and octyltrichlorosilane) have the same silanol hydrolysis product; octylsilanetriol. Therefore, since both substances share the same silanol hydrolysis product and undergo rapid and/or very rapid hydrolysis in contact with water, it is considered valid to read-across between the two substances.
The hydrolysis product, octylsilanetriol was determined to be potentially surface active (surface tension of 53 mN/m) using a relevant test method. Significant condensation of the test substance was observed in water and there was no indication of the test substance or organic group as product of hydrolysis in aqueous solution, thus the result is difficult to interpret. However, the surface activity observed was assumed to be as a result of a very small amount of the hydrolysis product which remained on the surface of the aqueous solution.
The surface activity of the hydrolysis product is observed to be weak and non-ionic, although there is the potential of formation of emulsions and micelles. The critical micelle concentration (CMC) of the substance is assumed to be very high. The polymerisation of the substance is a more pronounced effect than the formation of micelles at high concentration.
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