Polysulfides, bis[3-(triethoxysilyl)propyl]

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Data waiving:

study technically not feasible

Justification for data waiving:

the study does not need to be conducted because the substance is highly insoluble in water

Reference 2

Endpoint:

hydrolysis

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) 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

pH:

4

DT50:

>= 0.8 - <= 1.2 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

7

DT50:

>= 40 - <= 80 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

9

DT50:

>= 0.5 - <= 1 h

Remarks on result:

other: Temperatures; 20-25°C

Conclusions:

Hydrolysis half-life values of 0.8-1.2 h at pH 4, 40-80 h at pH 7 and 0.5-1.0 h at pH 9 and 20-25°C were obtained for the S2 constituent of the substance using an accepted calculation method. The result is considered to be reliable.

Reference 3

Endpoint:

hydrolysis

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) 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.

No.:

#1

No.:

#2

pH:

4

DT50:

>= 0.8 - <= 1.6 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

7

DT50:

>= 40 - <= 140 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

9

DT50:

>= 0.5 - <= 1.5

Remarks on result:

other: Temperatures; 20-25°C

Conclusions:

Hydrolysis half-life values of 0.8-1.6 h at pH 4, 40-140 h at pH 7 and 0.5-1.5 h at pH 9 and 20-25°C were obtained for the S5 identified named impurity of the substance using an accepted calculation method. The result is considered to be reliable.

Reference 4

Endpoint:

hydrolysis

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) 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

pH:

4

DT50:

>= 0.8 - <= 1.3 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

7

DT50:

>= 40 - <= 100 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

9

DT50:

>= 0.5 - <= 1.1 h

Remarks on result:

other: Temperatures; 20-25°C

Conclusions:

Hydrolysis half-life values of 0.8-1.3 h at pH 4, 40-100 h at pH 7 and 0.5-1.1 h at pH 9 and 20-25°C were obtained for the S3 constituent of the substance using an accepted calculation method. The result is considered to be reliable.

Reference 5

Endpoint:

hydrolysis

Type of information:

(Q)SAR

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

results derived from a valid (Q)SAR model, but not (completely) 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

pH:

4

DT50:

>= 0.8 - <= 1.4 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

7

DT50:

>= 40 - <= 120 h

Remarks on result:

other: Temperatures; 20-25°C

pH:

9

DT50:

>= 0.5 - <= 1.2 h

Remarks on result:

other: Temperatures; 20-25°C

Conclusions:

Hydrolysis half-life values of 0.8-1.4 h at pH 4, 40-120 h at pH 7 and 0.5-1.2 h at pH 9 and 20-25°C were obtained for the S4 constituent of the substance using an accepted calculation method. The result is considered to be reliable.

Description of key information

Hydrolysis half-lives at 20-25°C (QSAR):

S2 = 0.8 - 1.2 h at pH 4, 40 - 80 h at pH 7, 0.5 - 1 h at pH 9

S3 = 0.8 - 1.3 h at pH 4, 40 - 100 h at pH 7, 0.5 - 1.1 h at pH 9

S4 = 0.8 - 1.4 h at pH 4, 40 - 120 h at pH 7, 0.5 - 1.2 h at pH 9

S5 = 0.8 - 1.6 h at pH 4, 40 - 140 h at pH 7, 0.5 - 1.5 h at pH 9

Key value for chemical safety assessment

Half-life for hydrolysis:

140 h

at the temperature of:

20 °C

Additional information

The requirement to conduct a hydrolysis study for the substance is waived in accordance with Column 2 of REACH Annex VIII because the substance is insoluble in water. The constituents of the substance have water solubility values of < 1 mg/l.

 

The hydrolysis rates of the constituents; S2, S3 and S4, and S5 (identified as a named impurity), have been predicted using QSAR estimation methods. The half-lives are shown in Table 4.1.2 below.

 

As the hydrolysis reaction may be acid or base catalysed, the rate of reaction is expected to be slowest at around pH 7 and increase as the pH is raised or lowered. For an acid-base catalysed reaction in buffered solution, the measured rate constant is a linear combination of terms describing contributions from the uncatalyzed reaction as well as catalysis by hydronium, hydroxide, and general acids or bases.

 

k_obs = k₀+ k_H3O+[H₃O⁺] + k_OH_[OH^-] + k_a[acid] + k_b[base]

 

At extremes of pH and under standard hydrolysis test conditions, it is reasonable to suggest that the rate of hydrolysis is dominated by either the hydronium or hydroxide catalysed mechanism.

 

Therefore, at low pH:

 

k_obs≈k_H3O+[H₃O⁺]

 

At pH 4 [H₃O⁺] = 10^-4 mol dm^-3 and at pH 2 [H₃O⁺] =10^-2 mol dm^-3; therefore, k_obs at pH 2 should be approximately 100 times greater than k_obs at pH 4.

 

The half-life of a substance at pH 2 is calculated based on:

 

t_1/2(pH 2) = t_1/2(pH 4) / 100

 

The calculated half-lives of the constituents at pH 2 and 25°C are S2 = 0.012 h, S3 = 0.013 h, S4 = 0.014 h and S5 = 0.016 h.

 

Reaction rate increases with temperature therefore hydrolysis will be faster at physiologically relevant temperatures compared to standard laboratory conditions. Under ideal conditions, hydrolysis rate can be recalculated according to the equation:

 

DT₅₀(XºC) = DT₅₀(T) * e^(0.08.(T-X))

 

Where T = temperature for which data are available and X = target temperature.

 

The half-lives at 37.5ºC and pH 7 (relevant for lungs and blood) and pH 2 (relevant for conditions in the stomach following oral exposure) are calculated as shown in the table below. At 37.5°C and pH 5.5 (relevant for dermal exposure), the hydrolysis half-life is expected to be between the values for pH 4 and pH 7.

 

Table 4.1.2: Hydrolysis half-lives for constituents of the submission substance 

Constituent name	Abbreviation	Half-lives at 20-25°C (h)				Half-lives at 20-25°C (h)	Half-lives at 37.5°C
		pH 4	pH 5	pH 7	pH 9	pH 2	pH 2	pH 7
4,4,13,13-Tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane	S2	0.8 - 1.2	0.8 - 1.0	40-80	0.5 - 1.0	0.012	ca. 16 s	ca. 28 h
4,4,14,14-Tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane	S3	0.8 - 1.3	0.8 - 1.1	40-100	0.5 - 1.1	0.013	ca. 17 s	ca. 34 h
4,4,15,15-Tetraethoxy-3,16-dioxa-8,9,10,11-tetrathia-4,15-disilaoctadecane	S4	0.8 - 1.4	0.8 -1.2	40-120	0.5 - 1.2	0.014	ca. 19 s	ca. 42 h
4,4,16,16-Tetraethoxy-3,17-dioxa-8,9,10,11,12-pentathia-4,16-disilanonadecane	S5	0.8 - 1.6	0.8 - 1.2	40 - 140	0.5 - 1.5	0.016	ca. 21 s	ca. 51 h

 

The products of hydrolysis are bis[3-(trihydroxysilyl)propyl]polysulfides and ethanol.

Bis[3-(trihydroxysilyl)propyl]polysulfides is the hydrolysis product of the multiconstituent substance, consisting of the silanol hydrolysis products:

• For S2 constituent, (3-{[3-(trihydroxysilyl)propyl]disulfanyl}propyl)silanetriol
• For S3 constituent, (3-{[3-(trihydroxysilyl)propyl]trisulfanyl}propyl)silanetriol
• For S4 constituent, [3-({[3-(trihydroxysilyl)propyl]disulfanyl}disulfanyl)propyl]silanetriol
• For S5 named impurity, (3-{[3-(trihydroxysilyl)propyl]pentasulfanyl}propyl)silanetriol