Registration Dossier
Registration Dossier
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EC number: 445-890-5 | CAS number: 201290-01-9
Dissociation constant
Administrative data
Link to relevant study record(s)
Description of key information
Dissociation constant [N,N-bis(trimethylsilyl)aminopropylmethyldiethoxysilane]: not relevant, very rapid hydrolysis
Dissociation constant [3-(diethoxymethylsilyl)propylamine] (RNH3+ → RNH2): pKa = ca. 10
Dissociation constant 3-(dihydroxymethylsilyl)propylamine (diol group): pKa = ca. 12
Dissociation constant 3-(dihydroxymethylsilyl)propylamine (amino group): pKa = ca. 10
Dissociation constant [trimethylsilanol]: ca. 11
Key value for chemical safety assessment
Additional information
The requirement to conduct a dissociation constant for the substance is waived because in contact with water the substance hydrolyses very rapidly to form an intermediate hydrolysis product of 3-(diethoxy(methyl)silyl)propylamine and trimethylsilanol. The intermediate silanol hydrolysis product, 3-(diethoxy(methyl)silyl)propylamine also undergoes further hydrolysis to form 3-(dihydroxymethylsilyl)propylamine and ethanol.
The amine group present in 3-(diethoxymethylsilyl)propylamine has a predicted pKa of approximately 10. There are no reliable measured data for the dissociation constant of 3-(dihydroxymethylsilyl)propylamine.The typical dissociation constants for the hydroxyl protons of silanediols are available from studies in other silanediols. It is appropriate to read-across dissociation constant data for 3-(dihdroxymethylsilyl)propylamine from dimethylsilanediol. This suggests that silanols are not expected to undergo significant dissociation within the range of pH relevant in the environment or in vivo.
Dimethylsilanediol is reported in a secondary source to have a first dissociation constant of 11.9.
Also trimethylsilanol has a reported pKa value of approximately 11.
The amine group present in both the parent substance and the silanol hydrolysis product is basic. The pKa is not known but an indicative read-across substance would be ethanolamine. This has a basic pKa of 9.5 (Haynes 2010). The amino group present in 3-(diethoxymethylsilyl)propylamine has a predicted basic pKa of 10.4. The read-across and the prediction are in agreement that the pKa of this group is approximately 10.
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