Aqueous phase hydration and hydrate acidity of perfluoroalkyl and n:2 fluorotelomer aldehydes

Abstract

AbstractPerfluoroalkyl aldehydes (PFAlds) and n:2 fluorotelomer aldehydes (FTAlds) are degradation products of precursor compounds that include fluorotelomer alcohols, iodides, acrylates, phosphate esters, and other derivatives, as well as hydrofluorocarbons and hydrochlorofluorocarbons. The SPARC software program and comparative density functional theory (DFT) calculations were used to investigate the aqueous phase hydration equilibrium constants (K~hyd~) of PFAlds and FTAlds. DFT studies suggest that all PFAlds will be dominantly present as the hydrated form in aqueous solution. While SPARC correctly estimates the K~hyd~ for the C~1~ PFAld, it appears to incorrectly predict a large decline in K~hyd~ (particularly between C~1~ and C~2~) with increasing perfluoroalkyl chain length for this class of compounds. Both SPARC and DFT investigations suggest that FTAlds will not likely be substantially hydrated in aquatic systems or in vivo. Using corrected SPARC estimates, PFAld hydrates are expected to have pK~a~ values in the range of phenols (ca. 9 to 10), whereas n:2 FTAld hydrates are expected to have pK~a~ values ca. 2 to 3 units higher (ca. 12 to 13). Where relevant, the molecular and/or dissociated hydrate forms of PFAlds and FTAlds need to be explicitly considered in environmental, toxicological, and waste treatment investigations.