N-[3-(trimethoxysilyl)propyl-1,3-Benzenedimethanamine

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

(Q)SAR

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification

Justification for type of information:

See attached QMRFs/QPRFs

Principles of method if other than guideline:

The result was obtained using an appropriate QSAR method (see attached QMRF and QPRF for details)

The model for hydrolysis at pH 7 has been developed for and applies specifically to di- and tri-alkoxysilanes. It is a multiple linear regression based model with descriptors representing (i) steric effects of the alkoxy group, (ii) steric effects of the side-chain(s), and (iii) electronic effects of the side-chain(s).

The models for hydrolysis at pH 4, 5 and 9 have been developed for, and apply specifically to organosilicon compounds. They are linear regression based models where the descriptor is the half-life at pH 7.

Transformation products:

yes

No.:

#1

No.:

#2

Key result

pH:

4

DT50:

0.3 h

Remarks on result:

other: 20-25°C

Key result

pH:

7

DT50:

4.8 h

Remarks on result:

other: 20-25°C

Key result

pH:

9

DT50:

0.1 h

Remarks on result:

other: 20-25°C

Conclusions:

Hydrolysis half-life values at 20-25°C of 0.3 h at pH 4, 4.8 h at pH 7 and 0.1 h at pH 9 were obtained using an accepted calculation method. The result is considered to be reliable.

Description of key information

Hydrolysis half-lives at 20-25°C using QSAR method for the alkoxysilane group (Si-OMe):

Constituent 1 (alkoxysilane, Si-OMe group) = 0.3 h at pH 4, 4.8 h at pH 7 and 0.1 h at pH 9

Constituent 2 (silyl amine, Si-N group): very rapid hydrolysis in contact with water

Intermediate 2 (N-[3-(diihydroxy(methoxy)silyl)propyl]-1,3-benzenedimethanamine): <0.3 h at pH 4, <4.8 h at pH 7 and <0.1 h at pH 9.

Additional information

The submission substance is a multi-constituent substance containing two main constituents, N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine (Constituent 1) and 3-[(2,2-dimethoxy-1,2-azasilolidin-1-yl)benzenedimethanamine (Constituent 2).

The constituents undergo hydrolysis reactions. Based on the structure of the constituents and knowledge of alkoxysilane hydrolysis pathways, the expected hydrolysis pathways of the constituents are discussed below and illustrated in Figure 1 attached in Section 13.

Each constituent undergoes three consecutive hydrolysis reactions. The first hydrolysis step for Constituent 1 is loss of a methoxy group to give Intermediate 1, N-[3-(hydroxy(dimethoxy)silyl)propyl]-1,3-benzenedimethanamine and methanol. The first hydrolysis step for Constituent 2 is ring-opening at the Si-N bond. This also results in Intermediate 1, N-[3-(hydroxy(dimethoxy)silyl)propyl]-1,3-benzenedimethanamine (but not methanol). Intermediate 1 undergoes two further hydrolysis steps involving loss of its two methoxy groups to give Intermediate 2 (N-[3-(diihydroxy(methoxy)silyl)propyl]-1,3-benzenedimethanamine) and the final hydrolysis product (N-[3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine). Therefore, the intermediate and final silicon-containing hydrolysis products are the same for Constituent 1 and Constituent 2. The co-product of hydrolysis is methanol for both constituents (3 moles for Constituent 1 and 2 moles for Constituent 2).

 

Constituent 1 is a trimethoxysilane. The half-lives at pH 4, pH 7 and pH 9 at 20-25°C have been calculated using a validated QSAR estimation method. The calculated half-lives are 0.3 h at pH 4, 4.8 h at pH 7 and 0.1 h at pH 9. These half-lives refer to degradation of the parent substance (k₁). In general, for trialkoxysilanes the first step is the slowest and rate limiting factor. Each successive step is at least as fast as the previous one (k₁< k₂< k₃) and often approximately twice as fast as the previous one (Spivack et al 1997). Therefore, the half-lives for the second and third steps of the hydrolysis reaction are estimated to be less than those for the first-step: <0.3 h at pH 4, <4.8 h at pH 7 and <0.1 h at pH 9.

In addition to the alkoxysilane (Si-OMe) groups that are present in both constituents, Constituent 2 (3-[(2,2-dimethoxy-1,2-azasilolidin-1-yl)benzenedimethanamine) also contains a silyl amine (Si-N) group. The Si-N bond is known to be highly susceptible to hydrolysis by both acid-catalysed and base-catalysed mechanisms (Marcinick 2009). Therefore, the silyl amine bond present in Constituent 2 will undergo very rapid hydrolysis in contact with water. The half-life is estimated as <1 minute at pH 4, pH 7 and pH 9. The intermediate hydrolysis product produced by this reaction is N-[3-(hydroxy(dimethoxy)silyl)propyl]-1,3-benzenedimethanamine (Intermediate 1). As discussed for Constituent 1 above, the half-lives of Intermediate 1 and Intermediate 2 (N-[3-(dihydroxy(methoxy)silyl)propyl]-1,3-benzenedimethanamine) are estimated to be <0.3 h at pH 4, <4.8 h at pH 7 and <0.1 h at pH 9.

In the biodegradation study (Kayashima 2002), the submission substance was observed to immediately undergo hydrolysis in contact with water. From the result of the qualitative analysis of the residual components using LC-MS, one peak which correspond to the residual component (assumed to be the final hydrolysis product) was detected on the total ion chromatography in each of the test solutions (water + test item) and (sludge + test item). Similarly, from the GC analysis, the theoretical amount of methanol was detected in the test solution (water + test item) but not in the test solutions (sludge + test item). When the theoretical amount of methanol is produced and biodegraded, the average residual DOC amount (12.4 mgC) and the measured BOD value (11.9 to 14.6 mg) in the test solutions (sludge + test item) approximated the calculated DOC and TOD values of 13.7 mgC and 13.4 mgC respectively.

The hydrolysis half-lives are shown in Table 5.1 below.

Table 5.1: Hydrolysis half-lives for the constituents of the submission substance

Constituent name	Constituent Number	Step	Half-lives at 20-25°C
			pH 4	pH 7	pH 9
N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine	1	First -	0.3 h	4.8 h	0.1 h
N-[3-(trimethoxysilyl)propyl]-1,3-benzenedimethanamine	1	Second and third	<0.3 h	<4.8 h	<0.1 h
3-[(2,2-dimethoxy-1,2-azasilolidin-1-yl)benzenedimethanamine	2	First	<1 min	<1 min	<1 min
3-[(2,2-dimethoxy-1,2-azasilolidin-1-yl)benzenedimethanamine	2	Second and third	<0.3 h	<4.8 h	<0.1 h

 

The ultimate products of hydrolysis are:

Constituent 1 [3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine (1 mole) and methanol (3 moles).

Constituent 2 [3-(trihydroxysilyl)propyl]-1,3-benzenedimethanamine (1 mole) and methanol (2 moles).

References:

Spivack J L, Pohl E R, Kochs P (1997). Organoalkoxysilanes, Organosilanols and Organosiloxanols. The Handbook of Environmental Chemistry Vol. 3 Part H. Organosilicon Materials (ed. by G. Chandra). Springer-Verlag Berlin Heidelberg 1997

Marcinick Bogdain (2009). Hydrosilylation, a Comprehensive Review on Recent Advances. Springer Verlag pp289 -290.