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EC number: 297-566-6 | CAS number: 93642-68-3
Dissociation constant
Administrative data
Link to relevant study record(s)
Description of key information
Dissociation constant [3-[3-(triethoxysilyl)propyl]oxolane-2,5-dione]: not relevant
Dissociation constant [2-[3-(triethoxysilyl)propyl]butanedioic acid] (butanedioate group): 4.21 at 25°C
Dissociation constant [2-[3-(trihydroxysilyl)propyl]butanedioic acid] (triol group): approximately 10 at 22°C
Key value for chemical safety assessment
Additional information
The requirement to conduct a dissociation constant study for the substance is waived because in contact with water, it hydrolyses very rapidly to form an intermediate ethoxysilane hydrolysis product, 2-[3-(triethoxysilyl)propyl]butanedioic acid. The ultimate silanol hydrolysis product is 2-[3-(trihydroxysilyl)propyl]butanedioic acid and ethanol. There are no reliable measured data for the dissociation constant of 2-[3-(trihydroxysilyl)propyl]butanedioic acid. The typical dissociation constants for the hydroxyl protons of silanetriols are available from studies on other silanetriols. It is appropriate to read across dissociation constant data for 2-[3-(trihydroxysilyl)propyl]butanedioic acid from phenylsilanetriol. This suggests that silanols are not expected to undergo significant dissociation within the range of pH relevant in the environment or in vivo. Phenylsilanetriol has a measured first dissociation constant of approximately 10 at 22°C in a reliable study using a relevant test method, (reliability 1, read-across conclusion given reliability 2). Additional information is given in a supporting report (PFA, 2013b) attached to Section 13.
The butanedioate group is acidic and will therefore ionise in aqueous solution. Butanedioic acid has a reported pKa of 4.21 at 25°C (Haynes 2010). Similarly, in Dean 1987, pKa values of pKa1 = 4.207 and pKa2 = 5.635 at 25°C were reported for butanedioic acid.
Reference:
Dean J.A (1987). Handbook of Organic Chemistry. New York, NY: McGraw-Hill Book Co., p. 8-50.
Haynes W M, Lide D R (2010). CRC Handbook of Chemistry and Physics: A Ready-Reference Book of Chemical and Physical Data. 91st edition, CRC Press, Boca Raton.
Peter Fisk Associates (2013b). Peter Fisk Associates, Dissociation constant Analogue report, PFA.300.001.001
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