Reaction mass of (4-{[4-(diphenylsulfanylium)phenyl]sulfanyl}phenyl)diphenylsulfonium bishexafluorophosphate

Endpoint summary

Additional information

Note that much of the data was proved by ECHA under the 12 year data access rule. No robust summary was available at the time of preparation of this document and some key data was not included in the information from ECHA.

 

The substance will rapidly degrade in light (the function is UV curing agent) ). Analysis from fish and Daphnia testing using semi-static conditions reported up to 75% loss of test substance under light conditions over 24 hours.

 

 

The limited data provided by ECHA indicates that the substance reaches 62% degradation in 28 days when tested at 10 mg/L and 39.3% biodegradation when tested at 20 mg/L. These results indicate that the substance can be readily biodegraded under specific conditions.

 

The adsorption coefficient study was not performed as part of the original registration (Notification under 6th Amendment), but estimates by established modelling methods are considered sufficient to provide adequate information for risk assessment purposes. It must also be noted that exposure to the environment of the substance is unlikely as the substance will quickly breakdown in light and will lose its identity in waste water treatment processes. The photolysis products are being assessed.

 

Limited information on a hydrolysis study was provided, but from the apparent stability in water in this study and from the poor stability as a result of the fish and Daphnia tests, it appears likely that this study was performed in the dark. This is consistent with accepted good practice. It can be concluded that the substance will degrade in the presence of light in water, but not in the absence of light.

 

Further investigations into the identity of the degradation products from reaction in light and water are planned and these degradation products will be assessed.

 

 

Photodecomposition information

The test substance is a multi-constituent substance consisting of mono and di-sulphonium salts, used in UV curing.

 

 

Under UV irradiation, the cationic salt decomposes to produce a proton, together with several other photoproducts. The proton coupled with the anion provides the Bronsted acid that is involved in the ring opening epoxy polymerisation process. Ref 1,2. Heterolytic cleavage is the dominant pathway.

 

 

A hydrogen donor is required in the process and this will invariably be the epoxy oligomer and the polyether that is formed.

 

An aryl cation is first formed in cage. The release of a proton, which forms the Bronsted acid via the hydrogen donor, produces a substituted aryl, usually bound to the oligomer. Diphenyl sulphide and the three isomers of phenylthiobiphenyl are the main photoproducts, all bringing odour and the characteristic sulphury smell very noticeable immediately after cure.

The latter species are also responsible for some yellowing that occurs with sulphonium salts.

 

 

There are other minor photo and thermal reactions that lead, via homolytic cleavage, to different by-products, some of which may be significant to the curing process and the application (see below). For example, an unsubstituted aryl group in the cationic salt will produce a phenyl radical. This may lead to the formation of benzene from hydrogen abstraction (oligomeric donor) and biphenyl from radical-radical interaction. 

 

 

In UV curing, a high density of reactive species is produced and radical interactions, rather than abstraction are more likely. While benzene may be formed in trace amounts, it is a significant toxicological hazard for some applications. However, benzene should be considered in the context of a variety of exposure scenarios both natural and synthetic. Ref 3.

 

 

Biphenyl is a registered food anti-oxidant and is considered harmless. 

Subsequent thermal treatment, sterilisation etc. of products such as metal cans will remove these photoproducts and any other odorous by-products. Despite the release, in some cases, of these odorous photoproducts, cationic sulphonium salts have been assessed for safety and migration under FDA tests and found suitable for printing inks for polyolefin stock and food packaging applications. Ref 4.

 

 

Diphenylsulphide is the major photoproduct. Biphenyl and benzene occur in trace amounts.

 

 

References:

 

1. Photoinitiators for free radical, cationic and anionic photopolymerisation. 2nd edition. (Volume III of Chemistry & technology of UV & EB formulation for coatings, inks and paints.) J. V. Crivello and K. Dietliker. Ed G Bradley.           Wiley/SITA series, 1998. pp 415-419.

 

2. ‘New sulphonium salt based photoinitiators for cationic photopolymerisation.’ M. Hofer, C. Heller, R. Liska. RadTech Eu. Conf. Proc. 2007. Posters – Advances in photochemistry and polymerisation.

 

3. ‘Cationic systems are not at a crossroads.’ R. Holman. PRA RADnews. Spring 2000, p32.

 

4.  ‘Cationic UV ink migration and safety assessment.’ J. W. Carter, M. J. Jupina. RadTech Eu. Conf. Proc. 1997, pp250-258.

 

AG. April 2010.