1,1,1,2,2,3,4,5,5,5-decafluoro-3-methoxy-4-(trifluoromethyl)pentane

Endpoint summary

Additional information

HFE s-601 is stable to abiotic degradation. Hydrolysis of HFE s-601 is not expected based on lack of hydrolyzable structural elements. A hydrolysis test was deemed unreliable due to formation of a gas phase in all test vessels by end of test. Indirect phototransformation in the gas phase has a estimated lifetime of 3.8 years based on measured rate constant. The degradation pathway and products of HFE s-601 were not determined.  However, the pathway for HFE s-601 in the environment or in vivo can be predicted based on published data for CAS# 297730-93-9 [Hexane, 1,1,1,2,3,4,4,5,5,6,6,6-dodecafluoro-2-(trifluoromethyl)-3-ethoxy-].  CAS# 297730-93-9 differs from HFE s-601 by having one additional difluoromethylene group in the perfluoroalkyl moiety (i.e., a branched perfluoroheptyl group rather than a branched perfluorohexyl group) and by being an ethyl, rather than methyl, ether.  Atmospheric fate of CAS# 297730-93-3 was reported in Goto et al., 2002. Using infrared spectroscopy and reactivity characteristics, Goto et al. 2002 proposed a degradative pathway, based on reaction with either hydroxyl or chlorine radical. The first step is oxidation of the non-fluorinated ethyl ether group to either an acetate ester (major product) or formate ester (minor product). This transformation was oxygen dependent.  It should be noted that HFE s-601 contains a methoxy, rather than ethoxy, group, and the overall degradation pathway is much simpler.  Reactions leading to an acetate ester are not possible, and the formate ester is sole expected product.  This is exactly the result found by Wallington, et al. (1997) and Chen et al (2011) for 1 -methoxy 1,1,2,2,3,3,4,4,4-nonafluorobutane (EC# 422-270-2).  That is, 1-methoxy 1,1,2,2,3,3,4,4,4-nonafluorobutane was converted to 1,1,2,2,3,3,4,4,4-nonafluorobutyl formate.  By analogy, CAS# is 132182-92-4 would be converted to 1,1,1,2,2,3,4,5,5,5-decafluoro-4-(trifluoromethyl)pentyl 3-formate.

The analogous perfluoroalkyl esters were found to be subject to photolysis.  Indirect phototransformation of formate esters was found to occur at approximately the same rate as the parents or slower (Wallington et al., 1997; Chen et al., 2011; Goto et al., 2002).  In the case of perfluorobutyl formate, the ultimate degradation products were either carbonyl difluoride (from the normal isomer) or a 2:1 mixture of carbonyl difluoride and perfluoroacetyl fluoride (from the isobutyl isomer).  Goto et al. did not characterize photodegradation products of the esters.  In addition, Chen et al.(2004) examined photolysis of authentic samples of perfluoroethyl and perfluoropropyl formate with hydroxyl radical, whereas perfluorobutyl formate phototransformation was studied on the reaction products of 1-methoxy 1,1,2,2,3,3,4,4,4-nonafluorobutane (Chen et al., 2011).  While all cases direct UV photolysis of the esters was significant enough to interfere with their measurements, details sufficient to allow extrapolation from their experimental equipment to direct photolysis in the atmosphere were not provided.  In contrast, Nohara et al. (2001) examined photoreaction of a series of methyl perfluoroalkyl ethers with chlorine radicals.  The resulting formates were produced in 1:1 molar yield and reacted more slowly than the parent ether molecules.  In addition to carbonyl difluoride, a series of perfluoroalkyl fluoride with chain length 1, 2, or 3 carbons shorter than the parent were found through conversion of a perfluoroalkoxy radical to a perfluorinated alcohol and subsequent dehydrofluorination (it should be noted that this process depends on presence of HO2 and would occur in air with high levels of photooxidants).  Such a reaction sequence is not possible for HFE s-601 as only one fluorine atom is in the geminal position.  Dehydrofluorination can proceed only as far as a ketone, not a carboxylic acid (see below)

The hydrolytic instability of perfluoroalkyl esters due to inductive effects of the fluorine substituent has long been known (Pavlik and Toren, 1970).  Uchimara et al. (2003) performed ab initio calculations on fluorinated and non-fluorinated methyl acetate compounds. They concluded that inductive effects of fluorine substitution would stabilize the tetrahedral hydrolysis intermediate and increase the reaction rate. They speculated that neutral hydrolysis may also be potentiated by induction. Therefore, hydrolysis of dissolved ester is likely to occur on a timescale of minutes.  Hydrolysis of the ester from HFE s-601 would lead to a perfluorinated secondary alcohol.  Perfluorinated alcohols undergo spontaneous dehydrofluorination as noted earlier.  In the case of a secondary alcohol, this process can proceed only to the formation of a ketone.  For HFE s-601 phototransformation products dehydrofluorination leads to 1,1,1,2,2,4,5,5,5-nonafluoro-4-(trifluoromethyl)-3-pentanone (CAS# 756-13-8).  This material is registered under REACH and its photolytic and hydrolytic products are well known.

In two closed-bottle tests of biodegradability, no biodegradation of HFE s-601 was observed.  This suggests that metabolism of HFE s-601 in vivo is not likely.  In the unlikely event that biologically mediated oxidation were to occur, oxidase activity would be centered on the methoxy group similar to what has been observed in phototransformation experiments.

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