Dimethoxymethylvinylsilane

Endpoint summary

Description of key information

Read-across studies for skin irritation, conducted with trimethoxy(vinyl)silane and triethoxy(vinyl)silane found them not irritating to rabbit skin. Similarly, the studies for eye irritation conducted  trimethoxy(vinyl)silane and triethoxy(vinyl)silane found them not irritating to rabbit eyes.

Key value for chemical safety assessment

Skin irritation / corrosion

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Eye irritation

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (not irritating)

Respiratory irritation

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No in vitro or in vivo skin and eye irritation data are available for the registered substance. Reliable data are therefore read across from related alkoxysilanes as weight of evidence for these endpoints.

In a skin irritation study with triethoxy(vinyl)silane (WIL, 1998), the test substance was concluded to be slightly irritating to the skin of rabbits. However, the observed irritation did not meet the criteria for classification under Regulation (EC) No 1272/2008. 3 rabbits per sex were treated with 0.5 ml of the neat test substance for 4 h. The mean scores (over 24, 48, and 72 h) were 0.9 for erythema and 0.1 for edema reactions. Desquamation was observed in 1/6 animals after 72 h and was fully reversible within 11 days. Erythema and edema reactions were fully reversible within 9 days and 48 h, respectively.

The trimethoxy(vinyl)silane study for skin irritation found the test material not irritating to the skin of rabbits (Consultox 1976). There were no signs of erythema or edema at any time point.  The Primary Irritation Index was 0.0 so the test material was considered a non-irritant under these conditions.

In an eye irritation study with triethoxy(vinyl)silane (WIL, 1998), the test substance was not irritating to the eyes of rabbits. 2 male and 4 female rabbits were treated with 0.1 ml of the neat test substance and were observed up to 72 h. No washing was performed after treatment with the test substance. Minor (grade 1) conjunctival effects were observed in 6/6 animals at 1 h, in 2/6 animals at 24 h and in 1/6 animals at 48 h, but no corneal or iridial effects were observed. The mean score over 24, 48, and 72 h was 0.1 for conjunctivae and was fully reversible within 48 h. Chemosis mean score was 0.1 with a maximum grade of 1 and was fully reversible within 72 h.

The trimethoxy(vinyl)silane study for eye irritation found the test material not irritating to the eyes of rabbits (Hoechst 1991). The conjunctiva of the animals showed marked hyperaemia and redness and slight conjunctival swelling was evident. Irritation was only observed 30 - 60 minutes post application; all effects were reversible within 1 day.

READ-ACROSS JUSTIFICATION

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint. In the case of irritation the relevant properties are structural similarity as well as physical-chemical properties in the same range. In the following paragraphs the proposed read-across from trimethoxy(vinyl)silane and triethoxy(vinyl)silane to dimethoxy(methyl)vinylsilane is evaluated point by point.

A report considering read across for all endpoints is attached in Section 13.

Read-across hypothesis

The hypothesis is that source and target substances have similar toxicological properties because they are structurally similar and hydrolyse to similar silicon-containing hydrolysis products. The non-silanol hydrolysis products, methanol and ethanol, do not contribute to any adverse effects for irritation at the relevant concentrations based on publicly available information. This is discussed further below.

Read-across justification

The predicted hydrolysis half-lives of the registered substance, dimethoxy(methyl)vinylsilane, are 18.3 minutes at pH 7, <2 minutes at pH 2, and 0.7 minutes at pH 9, all at 25^oC; at 37.5^oC and at pH 7 and 2 the predicted half-lives are 0.1 hours and 5 seconds respectively. The products of hydrolysis are methylvinylsilanediol and methanol.

The read-across substance triethoxy(vinyl)silane has predicted hydrolysis half-lives at 20-25°C of 0.1 hours at pH 4, 0.2 hours at pH 5 and 0.02 hours at pH 9. As the hydrolysis reaction may be acid or base catalysed, the rate of reaction is expected to be slowest at pH 7 and increase as the pH is raised or lowered. The hydrolysis products are vinylsilanetriol and ethanol.

The read-across substance trimethoxy(vinyl)silane has predicted hydrolysis half-lives at 25°C of 0.1 hours at pH 7, 0.04 hours at pH 4, and 0.004 hours at pH 9. The hydrolysis products are vinylsilanetriol and methanol.

Therefore, the predicted half-lives for the registration and read-across substances at physiological pH are generally comparable so during exposure similar levels of parent and hydrolysis products will be present and so read-across from triethoxy(vinyl)silane and trimethoxy(vinyl)silane to dimethoxy(methyl)vinylsilane for irritation is valid.

Analogue approach justification

(a) Structural similarity

The registration and read-across substances are structurally similar and are members of an analogue group of methylvinyl silane substances. All contain a silicon atom to which is attached to a vinyl group which is identical for all three. The registered substance has two alkoxy groups bound to silicon, the read-across substances have three. For the registered substance the two alkoxy groups are methoxy, the read-across substance trimethoxy(vinyl)silane has three such groups, while for the other read-across substance triethoxy(vinyl)silane, the three alkoxy groups are ethoxy. All hydrolyse rapidly to produce the similar silicon-containing hydrolysis products, methylvinylsilanediol or vinylsilanetriol and methanol or ethanol.

(b) Similar physicochemical characteristics

The key physicochemical parameters are summarised below.

Table: Key physicochemical parameters

	Target (registration substance)	Source (read-across substance	Source (read-across substance
CAS number	016753-62-1	000078-08-0	002768-02-7
EC number	240-816-6	201-081-7	220-449-8
Chemical Name	dimethoxy(methyl)vinylsilane	triethoxy(vinyl)silane	trimethoxy(vinyl)silane
Molecular weight  (gmol^-1)	132.23	190.31	148.23
log Kow(parent)	2.3	3	Not applicable
log Kow(silicon-containing hydrolysis product)	-0.1	-2.0	-2.0
Water solubility (parent)	3000 mg/L	930 mg/L	3E+04 mg/L
Water solubility (silicon-containing hydrolysis product)	5E+05 mg/L	1E+06 mg/L	1E+06 mg/L
Vapour pressure (parent)	3000 Pa	304 Pa	1190 Pa
Vapour pressure (silicon-containing hydrolysis product)	2.1 Pa	0.02 Pa	0.02 Pa

 

(c) Discussion of irritation properties of the non-silanol hydrolysis products

The non-silanol hydrolysis products, methanol and ethanol, do not contribute to any irritant effects at the relevant concentrations based on publicly available information.

Justification for selection of skin irritation / corrosion endpoint:
One study was conducted according to an appropriate guideline and in compliance with GLP, the other was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Justification for selection of eye irritation endpoint:
Studies were conducted according to an appropriate guideline and in compliance with GLP.

Justification for classification or non-classification

Based on the available read-across data from trimethoxy(vinyl)silane and triethoxy(vinyl)silane, dimethoxy(methyl)vinylsilane does not require classification for skin or eye irritation according to Regulation (EC) 1272/2008.