[No public or meaningful name is available]

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

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 and falling into its applicability domain, with adequate and reliable documentation / justification

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

No.:

#3

pH:

4

DT50:

<= 0.3 h

Remarks on result:

other: 20-25°C

Remarks:

The result is for the cis and trans isomers

pH:

7

DT50:

<= 5.5 h

Remarks on result:

other: 20-25°C

Remarks:

The result is for the cis and trans isomers

pH:

9

DT50:

<= 0.1 h

Remarks on result:

other: 20-25°C

Remarks:

The result is for the cis and trans isomers

Conclusions:

Hydrolysis half-life values at 20-25°C of ≤5.5 h at pH 7, ≤0.3 h at pH 4 and ≤0.1 h at pH 9 were obtained for the cis and trans isomers of Constituent 1 using an accepted calculation method. The result is considered to be reliable.

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 and falling into its applicability domain, with adequate and reliable documentation / justification

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:

0.1 h

Remarks on result:

other: 20-25°C

pH:

5

DT50:

0.2 h

Remarks on result:

other: 20-25°C

pH:

7

DT50:

1.6 h

Remarks on result:

other: 20-25°C

pH:

9

DT50:

0.03 h

Remarks on result:

other: 20-25°C

Conclusions:

Hydrolysis half-life values at 20-25°C of 0.1 h at pH 4, 1.6 h at pH 7 and 0.03 h at pH 9 were obtained for Constituent 2 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:

Constituents 1a and 1b [cis and trans isomers] = ≤5.5 h at pH 7, ≤0.3 h at pH 4 and ≤0.1 h at pH 9

Constituent 2 = 1.6 h at pH 7, 0.1 h at pH 4 and 0.03 h at pH 9

Additional information

The submission substance is a multi-constituent substance. Each constituent contains two or three Si-OR’ groups which can hydrolyse to form Si-OH and ROH. The hydrolysis study is not a requirement at Annex VII but information about hydrolysis rates is important for the interpretation of other studies. Therefore, predictions for the rate of hydrolysis of the constituents are made using a validated QSAR method.

Constituent 1a and Constituent 1b: 1-[(2-ethylhexyl)oxy]propenyloxydimethoxy(methyl)silane (combined cis and trans isomers)

The predicted half-lives for degradation of Constituents 1a and 1b are ≤5.5 h at pH 7, ≤0.3 h at pH 4 and ≤0.1 h at pH 9 and 20-25°C. The QSAR method has been developed for alkoxysilanes. Constituents 1a and 1b contain a 1-[(2-ethylhexyl)oxy]propenyloxy group (as well as the two methoxy groups). There are no substances in the training set with this, or similar groups. This Si-OR’ group is expected to hydrolyse more rapidly than a similarly sized alkoxy group because both the carbon-carbon double bond and the second oxygen would weaken the Si-O bond electronically. This would speed up the hydrolysis. In addition, this group has some structural similarity with Si-carboxylate type structures that hydrolyse very rapidly. Therefore, the hydrolysis half-lives are reported as less than or equal to the predicted values.

The hydrolysis products are methylsilanetriol (1 mole), 1-[(2-ethylhexyl)oxy]prop-1-en-1-ol (1 mole) and methanol (2 moles). The 1-[(2-ethylhexyl)oxy]prop-1-en-1-ol formed by the hydrolysis of the Si-O bond undergoes tautomerism. This results in rearrangement of the enol-type structure to give the stable ester, 2-ethylhexyl propanoate. In the long-term, the hydrolysis product, 2-ethylhexyl propanoate may undergo further degradation/hydrolysis to the corresponding alcohol and acid; 2 -ethylhexylalcohol and propionic acid. This is supported by the observation made in a ready biodegradation study (Sudo 1995) where the products of degradation were reported as methylsilanetriol, propionic acid, methanol and 2-ethylhexylalcohol within the time scale of the study (28 days). The hydrolysis half-life is not known but this is expected to be slow at standard environmental temperature and pH (Mabey W and Mill T, 1978).

Therefore, the properties of 2-ethylhexyl propanoate, methanol and methylsilanetriol are considered in the chemical safety assessment.

Constituent 2: 2-ethylhexyl-3-[dimethoxy(methyl)silyl]propanoate

The predicted half-lives for degradation of Constituent 2 are 1.6 h at pH 7, 0.1 h at pH 4 and 0.03 h at pH 9 and 20-25°C.

The hydrolysis products are 2-ethylhexyl-3-[dihydroxy(methyl)silyl]propanoate (1 mole) and methanol (2 moles).

Reference:

Mabey W and Mill T, Critical review of hydrolysis of organic compounds in water under environmental conditions, J. Phys. Chem. Ref. Data, Vol. 7, No. 2, 383-415, 1978.