Vapor Pressure and Intramolecular Hydrogen Bonding in Fluorotelomer Alcohols

Abstract

Vapor pressure and aqueous solubility are important parameters used to estimate the potential for transport of chemical substances in the atmosphere. For fluorotelomer alcohols (FTOHs), currently under scrutiny by environmental scientists as potential precursors of persistent perfluorocarboxylates (PFCAs), vapor pressure is the more significant property since these compounds are only very sparingly soluble in water. We have measured the vapor pressures of a homologous series of fluorotelomer alcohols, F(CF2CF2)nCH2CH2OH (n = 2-5), in the temperature range 21-250 degrees C by three independent methods: (a) a method suitable for very low vapor pressures at ambient temperatures (gas-saturation method), (b) an improved boiling point method at controlled pressures (Scott method), and (c) a novel method, requiring milligram quantities of substance, based on gas-phase NMR, a technique largely unfamiliar to chemists and holding promise for studies of relevance to environmental chemistry. The concordant values obtained indicate that recently published vapor pressure data overestimate the vapor pressure at ambient temperature, and therefore the volatility, of this series of fluorinated compounds. It was suggested that substantial intramolecular -O-H...F- hydrogen bonding between the hydroxylic proton and the two fluorines next to the ethanol moiety was responsible for their putative high volatility. Therefore, we have used gas-phase NMR, gas-phase FTIR, 2D NMR heteronuclear Overhauser effect measurements, and high-level ab initio computations to investigate the intramolecular hydrogen bonding in fluorotelomer alcohols. Our studies unequivocally show that hydrogen bonding of this type is not significant and cannot contribute to and cause unusual volatility. The substantially lower vapor pressure at ambient temperatures than previously reported resulting from our work is important in developing a valid understanding of the environmental transport behavior of this class of compounds.

Using COSMOtherm to predict physicochemical properties of poly- and perfluorinated alkyl substances (PFASs)

“…In agreement with previous studies, [21,28,29] we found several energetically stable conformers for FTOHs. These belong to two groups: stretched conformations (SCs) and conformations with an intramolecular hydrogen bond between the hydroxylic proton and fluorine attached to the C 3 carbon (electrostatically interacting conformations, EICs), Fig.…”

“…In particular, K AW estimates calculated from measured P L and S W deviated by up to one order of magnitude for 10 : 2 FTOH from the experimental K AW values. The observed low internal consistency of the experimental data indicates that there is likely a measurement error in one (or all) of P L , [29] S W [30,31] or K AW . [19] COSMO calculation results for other PFASs A complete list of PFASs examined in this study, for which there are few or no measured physicochemical properties available, is included in the Accessory publication (see Tables A30-A33, 130 chemicals in total).…”

“…Ϫ3 Ϫ2 Modelled property data (data generated in this study with COSMOtherm and concerning different conformers, data from Arp et al [21] ; y-axis) for four FTOHs (4 : 2, 6 : 2, 8 : 2 and 10 : 2) v. experimental data [19,[29][30][31]58] (x-axis). carbon chain of polyfluorinated alkyl substances that include CH 2 linkers.…”

“…Since the authors have not specified which measured values of S W and P L they used, the result cannot be exactly reproduced. However, in the case of 8 : 2 FTOH, if we convert the reported subcooled-liquid P L (Pa) (log P L ¼ 0.60 [29] ) into solubility in air (S A , mol L À1 ) (log S A ¼ À5.79) and combine it with the reported solid phase S W (mol L À1 ) (log S W ¼ À6.38 [30,31] ), we are able to estimate the K AW (log K AW ¼ 0.59) and find that is very close to the reported K AW (log K AW ¼ 0.58 [19] ). Therefore, it is likely that the K AW of 8 : 2 FTOH was overestimated, because P L for the subcooled liquid was combined with S W for the solid state.…”

Occurrence of fluorotelomer alcohols at two Alpine summits: sources, transport and temporal trends

“…Naphthalene is the most volatile compound with log P L and log K OA values of 1.60 and 5.19, [33] respectively. The comparable log P L and log K OA values of 6:2, 8:2 and 10:2 FTOH were À0.70-1.26 [34] and 5.26-5.72, [35,36] respectively, which implies that the breakthrough of FTOHs during field air sampling was also negligible. Moreover, a breakthrough experiment was conducted indoor at a temperature of 22-24 8C, which gave breakthrough rates of 18, 11 and 5 % for 6:2, 8:2 and 10:2 FTOH, respectively.…”