Perfluoroalkanoic Acids Research Articles

Thermodynamic implications of size, hydrophilicity, and fluorine content on perfluoroalkyl adsorption in NU‐1000

AbstractThe molecular mechanisms that drive adsorption are critical for engineering new adsorbents to capture environmental contaminants, such as perfluoroalkyl substances (PFAS). Metal–organic frameworks (MOFs) have been shown to adsorb some classes of PFAS, yet a fundamental understanding of how PFAS identity and water competition affect adsorption capacity is unknown. Here, grand canonical Monte Carlo simulations of perfluoroalkanoic acids (PFAAs) adsorption in the MOF NU‐1000 were performed with coadsorbed water and varying carbon chain length sizes to interrogate how PFAS structure affects adsorption capacity. We found that larger PFAAs adsorb favorably into NU‐1000 than shorter chain PFAAs due to the formation of pore‐filling aggregates that stabilize anionic adsorption to the node. Due to their size and hydrophilicity, shorter chains tend to limit interactions with the adsorbent. These insights offer directions for developing novel materials that promote aggregate formation to capture and retain a wider set of PFAS from aqueous solutions.

Quantification of 3,4-Dimethyl-1H-Pyrazole Using Ion-Pair LC-MS/MS on a Reversed-Phase Column.

Few methods exist for the analysis of the soil nitrification inhibitor 3,4-dimethyl-1H-pyrazole (3,4-DMP), which is a pesticide with the ability to reduce the production of nitrogenous greenhouse gases in soils as a result of fertilizer application. Due to its small size and polar nature, 3,4-DMP can be difficult to retain on an LC column, which makes diversion of a co-extracted soil matrix away from the MS/MS impossible. The current study aims to better control the retention time (RT) of 3,4-DMP. Additionally, 3,4-DMP-15N2 was synthesized and used as an internal standard for the soil extraction of 3,4-DMP. Perfluoroalkanoic acids were used as ion-pair reagents and were compared for their abilities to improve peak shape and RT, to better separate 3,4-DMP from the soil matrix without the need for cleanup during soil extraction. RTs increased with both the carbon number and the concentration of the perfluoroalkanoic acid, and this improved peak shape and height. Perfluorooctanoic acid performed best, and improved peak height (PH) and shape were obtained by increasing the flow rate, resulting in a better S/N than from formic acid. The method provided a 10-fold improvement limit of quantitation on the most sensitive existing method and the use of 3,4-DMP-15N2 as an internal standard resulted in recoveries of 101-107%. Ion-pair reagents drastically increased the retention of 3,4-DMP and allowed the re-use of old LC columns that may otherwise be discarded. Improved separation of 3,4-DMP from the soil matrix allowed much of the matrix to be diverted from the MS/MS spray chamber. Greater control of 3,4-DMP retention by the LC column resulting in the ability to separate 3,4-DMP from the soil matrix. The inclusion of ion-pair reagents only in the aqueous phase reduced ionization suppression of the analytes in the MS source.

New Epoxy Resin Polymerization Catalysts Based on N,N-Dimethylaminoalkylamides of Perfluoroalkanoic Acids

New Epoxy Resin Polymerization Catalysts Based on N,N-Dimethylaminoalkylamides of Perfluoroalkanoic Acids

Dissociation constants of perfluoroalkanoic acids

The dissociation constants of six selected perfluoroalkanoic acids (from perfluoropentanoic to perfluorodecanoic acid) were determined using neutralization potentiometric titration method. The values of determined dissociation constants ranges from pK a = 2.17 to 2.44, and they are in partial agreement with published data which have also been reviewed. The decrease of value of dissociation constant with increasing number of carbon in alkyl chain has been observed. Also, the increase of values of dissociation constants of perfluoroalkanoic acids in comparison with their nonfluorinated analogs has been confirmed.

Reaction of 3-carene with perfluoroalkanoic acids

The addition of perfluoroalkanoic acids to 3-carene involves opening of the cyclopropane ring at the peripheral bonds with formation of a mixture of isomeric p-menth-1-en-8-yl and m-menth-1-en-8-yl perfluoroalkanoates. The reaction rate decreases as the length of the perfluoroalkyl radical of the acid increases. Trichloroacetic acid reacted with 3-carene at a lower rate than does trifluoroacetic acid, but the products are analogous p-menth-1-en-8-yl and m-menth-1-en-8-yl trichloroacetates.

New Approaches to Measuring Sticky Molecules: Improvement of Instrumental Response Times Using Active Passivation.

A novel method has been developed to improve sampling system response times for nominally "sticky" molecules such as HNO3 and NH3. The method reported here makes use of active, continuous passivation, where the instrument interfaces are continuously exposed to 0.01-1 ppm of fluorinated acidic or basic surfactants. To reduce HNO3 response times, perfluoroheptanoic acid and perfluorobutanesulfonic acid vapors are evaluated as passivation species. 1H,1H-perfluorooctylamine is used to improve NH3 response times. The resulting time responses using the perfluoroalkanoic acids are on the order of 0.4-0.7 s for a 75% quantitative recovery of HNO3, and 1-5 s for 90% recovery. Similar response time improvements are seen in detection of NH3 using perfluorooctylamine (<1 s for a 75% recovery, ∼ 2 s for 90% recovery). This generally applicable methodology significantly improves the capability of eddy covariance flux and real-time plume-based measurements of highly polar molecules that have historically been hampered by slow response times due to adsorption on sampling system surfaces. The utility of this approach is demonstrated by field measurements of HNO3 eddy covariance fluxes in a central U.S. prairie.

Addition of perfluoroalkanoic acids to (R)-(+)-limonene

Perfluoroalkanoic acids with different lengths of the perfluoroalkyl radical selectively add under mild conditions to the exocyclic double C=C of limonene to give the corresponding Markovnikov adducts, α-terpinyl perfluoroalkanoates. The reaction in the presence of sulfuric acid 0°C involves both double C=C bonds in the limonene molecule with formation of p-menthane-1,8-diyl bis(perfluoroalkanoates).

Adsorption of perfluorinated compounds on thin‐film composite polyamide membranes

AbstractThe adsorption behavior of perfluorinated compounds (PFCs), of various chain lengths and two different functional groups, on widely used thin‐film composite polyamide membranes has been investigated. Three commercially available polyamide membranes and two classes of PFCs were evaluated: Dow‐Filmtech BW30, NF90, and NF270 membranes; perfluorosulfonic and perfluoroalkanoic acid with 5, 7, 9, and 11 carbon atoms. The adsorption of PFCs on the membranes strongly depended on the active skin‐top layer material of the membranes, solution chemistry, and structure of PFCs. The piperazine based NF270 membrane showed higher adsorption of PFCs compared to BW30 and NF90 membranes (FT‐30 type membranes). The BW30 membrane, which has a coating layer of aliphatic carbons and hydroxyl groups on the surface of the polyamide substrate, had less interaction with PFCs than the NF90 polyamide membrane had. The adsorption of PFCs increased with increasing ionic strength, decreasing pH, and in divalent ion solutions. PFCs with longer chain lengths and more hydrophobic functional groups showed more attractive interactions with thin‐film composite membranes and, thus, greater adsorption on the membranes. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

ChemInform Abstract: Perfluoroalkylation of Olefins by Electrooxidation of Perfluoroalkanoic Acids: Relations Between Product-Selectivity and Current Density and Structures of Olefins.

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Preparation and assessment of fluorous supported liquid membranes based on porous alumina

Fluorous media have gained a foothold in the synthetic and analytical communities. There is a need for membranes or films that have good selectivity for transport of molecules with fluorous tags. We show here that supported liquid membranes (SLMs) based on modified porous alumina have the desired properties. Hydrophobic alumina membranes were prepared by surface modification with perfluoroalkanoic acids. The initial contact angles of modified alumina membranes exceed 130°. FTIR shows the loss of –OH stretching modes and the gain of carboxylate carbonyl stretch as well as C–F stretching modes indicative of the surface modification. SEM shows no gross changes in the membrane morphology resulting from the modification. The resulting modified membranes readily imbibe and hold fluorous solvents forming SLMs. Cinnamyl alcohol ( 1) and its ester with 2H,2H,3H,3H-perfluorononanoic acid (HOOC–(CH 2) 2–(CF 2) 5CF 3) ( 2c) were employed as solutes in transport experiments with the membranes. Transport selectivity (ratio of permeabilities of 2c to 1) was used as a measure of effectiveness in the optimization of modification conditions. Conditions for the surface modification leading to maximum selectivity for transport of 2c over 1 by the resulting SLM were to reflux membranes in 3 mM Krytox 157FSH/HFE 7100 solution for 3 h. Finally, the influence of membrane pore size on transport rate and selectivity was investigated for cinnamyl alcohol and its esters with fluorous carboxylic acids HOOC–(CH 2) 2–(CF 2) n−1 CF 3, n = 2, 4, 6, 8. The transport rate for the smallest pore size (20 nm) and largest solute ( n = 8) is anomalously high. This may be due to solute being transported in the modification layer as well as solvent.

Emerging endocrine disrupters: perfluoroalkylated substances

In recent years, polyfluorinated chemicals (PFCs) have increasingly been used as surfactants in various industry- and consumer products, because of their unique properties as repellents of dirt, water and oils. The most well-known PFCs are perfluorooctane sulfonic acid (PFOS), perfluorooctanoic acid (PFOA) and their derivatives belonging to the group of perfluoroalkylated substances. The PFCs are very persistent in the environment, and some of them have been discovered as global pollutants of air, water, soil and wildlife and even found in remote polar areas. Bioaccumulation occurs also in humans, and everybody in our society has traces of these PFCs in their blood and internal organs such as the liver, kidneys, spleen, gall bladder and testes. In the blood, PFOS and PFOA are bound to serum proteins. The acute toxicity of the polyfluorinated substances is moderate but some substances can induce peroxisome proliferation in rat livers and may change the fluidity of cell membranes. Some of these PFCs, such as PFOS and PFOA, are potential developmental toxicants and are suspected endocrine disruptors with effects on sex hormone levels resulting in lower testosterone levels and higher oestradiol level. Other PFCs have oestrogenic effects in cell cultures. The industrial production of PFOS and its derivatives stopped in 2000, and the European Union has banned most uses from the summer of 2008. However, hundreds of related chemicals: homologues with shorter or longer alkyl chain, PFOA and telomers, which potentially may degrade to perfluoroalkanoic (carboxylic) acids, are not regulated.

Water evaporation rates across hydrophobic acid monolayers at equilibrium spreading pressure

The effect of alkanoic acid [CH 3(CH 2) n−2 COOH; HC n] and perfluoroalkanoic acid [CF 3(CF 2) n−2 COOH; FC n] monolayers on the water evaporation rate was investigated by thermogravimetry tracing the decrease in amount of water with time. The evaporation rate from the surface covered by a monolayer was measured as a function of temperature and hydrophobic chain length of the acids, where the monolayer was under an equilibrium spreading pressure. From thermal behavior of the crystallized acids, their solid states are C-type in crystalline state over the temperature range from 298.2 to 323.2 K. The dry air was flowed through a furnace tube of a thermogravimetry apparatus at the flow rate of 80 mL min −1, where the evaporation rate becomes almost constant irrespective of the flow rate. The temperature dependence of the evaporation rate was analyzed kinetically to evaluate the activation energy and thermodynamics values for the activated complex, which demonstrated that these values were almost the same for both alkanoic acids and perfluoroalkanoic acids, although the effect of perfluoroalkanoic acids on the evaporation rate was smaller than that of corresponding hydrogenated fatty acids. The difference in the evaporation rate between FC n and HC n was examined by atomic force microscopy (AFM), Brewster angle microscopy (BAM), surface potential (Δ V) at equilibrium spreading pressure, and Langmuir curve ( π – A isotherm), and their results were consistent and supported the difference.

The synthesis of new liquid–crystalline mesogens containing bicyclohexane units

The synthesis and mesomorphism characterization of new thermotropic derivatives of cis, trans and trans, trans-4,4′-bicyclohexyl-bis[4-(6-hydroxyhexan-1-oxy)benzoate] are described. This last intermediate produces a liquid crystalline diacrylate, with lower refractive indices than the well-known aromatic analogues, that allows to obtain polymeric network via UV photopolymerization. The acrylate is very useful to optimize the contrast of polymer dispersed liquid crystals (PDLCs). Moreover, the acylation of the intermediates previously mentioned, with alkanoic or perfluoro alkanoic acids give low-molecular liquid crystals that exhibit a broad temperature range of mesophases.

19F Fast Magic-Angle Spinning NMR Studies of Perfluoroalkanoic Acid Self-Assembled Monolayers

The bonding and dynamic properties of perfluoroalkanoic acid self-assembled monolayers (SAMs) on zirconia and titania powders were characterized by Fourier transform infrared and solid-state 19F magic-angle spinning NMR spectroscopy. The perfluoro fatty acids investigated included C(n)F(2n+1)CO2H, n = 7, 13, 15 and 17. The acids bind to both metal oxides via ionic carboxylate bonds, but complete monolayers are only formed on the zirconia. The shift of the CF3 group from -83 ppm in the bulk state to -85 ppm for the adsorbed monolayers is assigned to CF3 groups located at the air/monolayer interface. With the exception of the perfluorooctanoic acid, 19F spin lattice relaxation measurements indicate that the fluorocarbon chains of the adsorbed acids, even in the case of densely packed monolayers, are significantly more mobile than those in the bulk state. The motions associated with the enhanced mobility of the adsorbed acids are proposed to involve reorientations along the long chain axes. No evidence for chain melting in the fluorocarbon SAMs is found for temperatures well above the melting temperature of the bulk acids.

Changing mechanisms in the beta-cyclodextrin-mediated hydrolysis of phenyl esters of perfluoroalkanoic acids.

The rate of hydrolysis of esters CF(3)(CF(2))(n)COOPh (1 (n = 1), 2 (n = 2), and 3 (n = 6)) was measured at pH 6.00 and at pH higher than 9.00 in the presence of beta-cyclodextrin (beta-CD). For compounds 1 and 2 the reaction rate decreases as the beta-CD concentration increases, and they show saturation effects at all pH. It is suggested that the substrate forms an inclusion complex with cyclodextrin. Analysis of the rate data allows calculation of the association equilibrium constant, K(CD), the rate constant for the reaction of the included compound, k(c), and K(TS) which is the hypothetical association equilibrium constant for the transition state of the cyclodextrin-mediated reaction. The dependence of log K(CD) and log K(TS) with the number of atoms in the chain is different. We suggest that the reactions of 1 and 2 take place with the perfluorinated alkyl chain included in the cavity, whereas the transition state for the reaction of phenyl trifluoroacetate involves a complex with the aryl ring inside the cavity. At low pH the inhibition comes from the protection of the carbonyl group toward nucleophilic attack by water. In basic pH the reaction of HO(-) as an external nucleophile is also inhibited. The cyclodextrin-mediated reaction involves the ionized OH group at the rim of the cyclodextrin cavity with poor efficiency due to an unfavorable orientation of the substrate in the complex. On the other hand, the reaction of compound 3 is strongly accelerated by cyclodextrin because the association of the substrate with cyclodextrin competes with the monomer-aggregate equilibrium and at high enough cyclodextrin concentration the main species present in solution is the complex between 3 and cyclodextrin.

Scavenging of fluorinated N,N'-dialkylureas by hydrogen binding: a novel separation method for fluorous synthesis.

[reaction: see text] A dramatic solubility increase in fluorous solvents is observed for N,N'-di(polyfluoroalkyl)ureas when hydrogen binding complexes are formed with commercially available perfluoroalkanoic acid scavengers. As a case example, analytically pure peptides and esters are obtained using this novel separation method.

Determination of Acidity Constants of Perfluoroalkanoic Acids

Abstract Acidity constants (Ka) of perfluoroalkanoic acids were determined by pH titration and by electric conductivity for shorter alkanoic acids (C1 to C5) with 1 to 5 carbon atoms in the alkyl chain. The acidity constants obtained by the two methods are in good agreement. They increase from C1 (ethanoic) to C3 (butanoic acid) and then decrease from C3 to C5 (hexanoic acid) with increasing alkyl chain length. An abrupt decrease in the Ka value for the C5 acid occurred; the attempt to explain this in terms of viscosity of the solutions did not succeeded. The decrease in the Ka values with increasing alkyl chain length was substantiated by the values for C9 (decanoic) to C11 (dodecanoic) acids, which were determined from the solubility change with the solution pH. For the intermediate alkanoic acids (C6 to C8), the Ka values could not be determined precisely by these methods due to the extreme difficulty in separating the colloidal acid particles from the aqueous phase, because the particles have an emulsifying action of their own.

Investigations on the adsorption properties of surface-chemically pure sodium salts of perfluoroalkanoic acids

Equilibrium surface tension-concentration isotherms of sodium salts of perfluoroalkanoic acids (C 6C 10) have been determined experimentally at 295 K. The sodium salts used were prepared by neutralization of the corresponding perfluoroalkanoic acids with sodium hydroxide, and were recrystallized several times from aqueous alcoholic solutions. Stock solutions of the salts were purified additionally by a special procedure [K. Lunkenheimer, H.-J. Pergande and H. Krüger, Rev.Sci.Instrum. 58 (1987), 2313] to obtain ‘surface-chemical purity’. The adsorption parameters: — free enthalpy of adsorption, minimum surface area per molecule adsorbed, and interaction parameter — are obtained from the evaluation of the measured adsorption isotherms by means of a surface equation of state. The parameters provide new insights into the adsorption properties, unknown so far. The most interesting feature consists of a distinct dependence of the surface area demand on the perfluorocarbon chain length. Quantitative relationships between the surface parameters, the free enthalpy of adsorption and of micellization, and the number of carbon atoms are derived. These results are compared with data already available from the literature. The reasons for contradictory findings in the literature are discussed with respect to errors introduced by unsuitable measuring conditions and insufficient surfactant purity. Recommendations for obtaining more reliable and non-contradictory results are given.

Homologation of trifluoroacetimidoyl iodides by palladium-catalyzed carbonylation. An approach to α-amino perfluoroalkanoic acids.

Homologation of trifluoroacetimidoyl iodides and the related perfluoro-compounds by palladium-catalyst under CO(1atm)-atmosphere in the presence of alcohols gives α-imino perfluoroalkanoates which are transformed to α-amino perfluoroalkanoic acids.

Perfluoroalkylation of Olefins by Electrooxidation of Perfluoroalkanoic Acids: Relations between Product-Selectivity and Current Density and Structures of Olefins

Abstract Electrooxidation of perfluoroalkanoic acids RfCO2H (Rf = CF3, C3F7, C7F15 together with CHF2, CH2F) in the presence of electron-deficient olefins (methyl acrylate, methyl methacrylate, acrylamide, and acrylonitrile) provided perfluoroalkylated products. The electrolysis was conducted in MeCN–H2O (7 : 1) using platinum electrodes in an undivided cell. Dimerization of methyl acrylate accompanying perfluoroalkylation, occurs in 40–50% yield under 20 mA cm−2 current density. 1,2-Addition of trifluoromethyl or difluoromethyl radicals to carbon-carbon double bond predominates in acrylamide under the high current density (100–200 mA cm−2). On the other hand, 1,2-addition of trifluoromethyl and acetamido groups and 1,2-addition of trifluoromethyl and hydroxyl groups occur in the low current density ( &amp;lt; 5 mA cm−2) electrolysis of methyl methacrylate.