N-[3-(dimethoxymethylsilyl)propyl]ethylenediamine

Dissociation constant

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

dissociation constant

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

the study does not need to be conducted because the substance is hydrolytically unstable (half-life less than 12 hours)

Reference 2

Endpoint:

dissociation constant

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

accepted calculation method

Principles of method if other than guideline:

The pKa of the amine group was obtained using the SPARC on-line property calculator.

Dissociating properties:

yes

No.:

#1

pKa:

7

No.:

#2

pKa:

10

Conclusions:

The pKa for the diamine groups re 7 and 10 using an appropriate predictive method.

Reference 3

Endpoint:

dissociation constant

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

4 (not assignable)

Rationale for reliability incl. deficiencies:

secondary literature

Principles of method if other than guideline:

Titration method (no further details available)

GLP compliance:

not specified

Dissociating properties:

yes

No.:

#1

pKa:

11.9

Conclusions:

A dissociation constant of 11.9 was reported in a secondary literature for the substance dimethylsilanediol. The original reference was not available for review and no further information is available. The reliability of this result is not assignable.

Description of key information

Dissociation constant [N-[3-(dimethoxymethylsilyl)propyl]ethylenediamine]: not relevant due to very rapid hydrolysis in contact with water

Dissociation constant [di-amine group for parent and silanol hydrolysis product]: pKa approximately 10

Dissociation constant [dihydroxysilyl group of N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine]: pKa approximately 12

Additional information

The requirement to test the substance for dissociation constant is waived because in contact with water the substance hydrolyses very rapidly. The hydrolysis products in this case are N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine and methanol. There are no reliable measured data for the dissociation constant of the parent substance or hydrolysis product.

The amine groups in the parent substance and silanol hydrolysis products are basic and will gain a proton in aqueous solution to give a positively charged (cationic) species The dissociation constants of the di-amine group have been calculated using an appropriate predictive method to be approximately 7 and approximately 10. This means that they are present as a mixture of the singly and doubly ionised (cationic) forms at environmentally relevant pH.

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 N-[3-(dihydroxymethylsilyl)propyl]ethylenediamine 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.

Additional information is given in a supporting report (PFA 2013b) attached in Section 13.