Fluorination

Recent findings in the synthesis of perfluoro-hypofluorites, their reactivity and their use in the preparation of important perfluoro monomers are herein summarized and analyzed. The experimental conditions to induce free radical or electrophilic reactivity as well as their use as initiation system in the oxidation and oxypolimerization of fluorinated olefins are also presented.

Particular emphasis is dedicated to safety issues since organic hypofluorites have the tendency to self-decompose forming gaseous compounds.The hypofluorites considered in this review are: CF3OF, CF2(OF)2, CF3CF2OCF2OF, CF3OCF2CF2OCF2OF, CF3O(CF2O)nCF2OF, CF3OCF2CF2OF, (CF3)2CFOF (CF3)3COF, FS(O)2CF2CF2OF, CF3OCF2CF2CF2OF, cyclo-(CF2OCF2OCF)-CF2OF, (CF3)2N-CF2OF

A variety of arylalkynoic acids reacted with 1,3-diiodo-5,5-dimethylhydantoin and HF·pyridine in the presence of AgOAc to provide the corresponding 1-fluoro-2,2-diiodovi-nylarenes in good yields and high regioselectivity. In addition, Pd-catalyzed cross-coupling reaction of 1-fluoro-2,2-diiodovi-nylarenes afforded diaryl coupling products in the Suzuki reaction and monoaryl coupling products with high stereo-selectivity in the Hiyama reaction. It was found that C−F-activated borylation of fluoroalkenes using Pd catalyst afforded the vinylboranes with good yields. M any biological and medicinal products, as well as important functional materials, contain the fluorine functionality. 1 Substitution of hydrogen with fluorine in organic materials can dramatically change the reactivity and the chemical, physical, and biological properties of the corresponding compounds. 2 As a consequence, fluorinated compounds have recently gained considerable attention in various fields, and the number of methodologies introducing the fluorine functionality into organic compounds has increased drastically over the last few decades. 3 Fluoroalkene, one of the numerous fluorine-containing compounds, is an important structural motif found in many bioactive compounds and is a useful building block. 4 A variety of synthetic methods for fluoroalkenes have been reported in the literature, and hydrofluorination of alkynes is one such straightforward method (Scheme 1a). 5 Sadighi first reported hydrofluorination of alkynes using Au catalyst to furnish fluoroalkenes in good yields. A number of Au-catalyzed hydrofluorination reactions of alkynes have been developed by several groups. In addition, it was reported that alkynes having a carbonyl group could be converted into the corresponding fluoroalkenes under metal-free or copper catalysis conditions (Scheme 1b). 6 Moreover, fluoroalkene derivatives 1,2-bromofluoro-and 1,2-fluoroiodoalkenes have received considerable attention as useful fluorinated building blocks because these vinyl bromides and iodides can be further transformed into versatile molecules via cross-coupling reactions (Scheme 1c). Jiang demonstrated that 1,2-bromofluoroalkenes could be synthesized by the reaction of terminal alkynes with NBS/AgF. 7 Synthesis of 1,2-fluoroiodoalkenes was accomplished by the fluoroiodination of alkynes employing HF-based reagents along with the iodine reagents such as I 2 , Tol-IF 2 , IF 5 , PhIO, and 1,3-diiodo-5,5-dimethylhydantoin (DIH). 8 In contrast, much less attention has been paid toward gem-dihalo-substituted fluoroalkenes, although in theory, they are highly likely to be employed as coupling partners in the cross-coupling reactions for the preparation of mono-and disubstituted fluoroalkenes. It has been reported that the preparation of gem-dibromo-and gem-dichlorofluoroalkenes from aldehydes requires a multistep process (Scheme 1d). 9 Therefore, simple and one-step synthetic methods are required.

Infrared spectroscopy (FTIR) is a standard technique for the characterisation of organic materials in conservation science. This analytical technique is particularly interesting to analyse historical varnishes from cultural artefacts, as only minute samples are required. Some limitations apply, however, when analysing such chemically complex multi-component materials with interfering absorption bands. A previously introduced sample pre-treatment method using gaseous sulfur tetrafluoride SF4 has shown to widen the application fields of the IR-technique by improving its specificity. One of these new fields is its successful application to the characterisation of complex aged natural varnish and lacquer systems. The fluorination treatment leads to characteristic band shifts of four individual saturated and unsaturated acid groups attached at varying positions of the terpene backbone. This allows the separation of otherwise overlapping carbonyl bands of different ketones and ester groups. Based on this technique, inert and unique functional groups can be used as material specific markers to identify drying oil, shellac and different terpene resins in varnishes and lacquers. The proposed markers proved to be stable for several hundred years. These findings are particularly interesting, as it is now possible to trace such markers even in very old varnishes dating back to the 16th century – with a likewise simple technique.

–We report precise triple oxygen isotope data of bulk materials and separated fractions of several Shergotty–Nakhla–Chassigny (SNC) meteorites using enhanced laser-assisted fluorination technique. This study shows that SNCs have remarkably identical D 17 O and a narrow range in d 18 O values suggesting that these meteorites have assimilated negligibly small surface materials (<5%), which is undetectable in the oxygen isotope compositions reported here. Also, fractionation factors in coexisting silicate mineral pairs (px-ol and mask-ol) further demonstrate isotopic equilibrium at magmatic temperatures. We present a mass-dependent fractionation line for bulk materials with a slope of 0.526 AE 0.016 (1SE) comparable to the slope obtained in an earlier study (0.526 AE 0.013; Franchi et al. 1999). We also present a new Martian fractionation line for SNCs constructed from separated fractions (i.e., pyroxene, olivine, and maskelynite) with a slope of 0.532 AE 0.009 (1SE). The identical fractionation lines run above and parallel to our terrestrial fractionation line with D 17 O = 0.318 AE 0.016& (SD) for bulk materials and 0.316 AE 0.009& (SD) for separated fractions. The conformity in slopes and D 17 O between bulk materials and separated fractions confirm oxygen isotope homogeneity in the Martian mantle though recent studies suggest that the Martian lithosphere may potentially have multiple oxygen isotope reservoirs.

We present a detailed analysis of the effect of fluorination on the conformation of perfluorosuccinic acid in the solid state, using database analysis, crystal structure determination and computational analysis of molecular conformations. Our results indicate that perfluorosuccinic acid exhibits strikingly different conformational preferences to its hydrocarbon analogue despite similarity in molecular size, and that this difference in conformational behavior also extends to the pair of adipic and perfluoroadipic acids. A search of the Cambridge Structure Database indicates that our analysis is valid for neutral molecules, salts, cocrystals as well as for metal-organic materials, suggesting that fluorination provides a general means of modifying the shape of a molecular building block without changing its size. The difference in molecular shape between hydrocarbon and perfluorocarbon molecules is expected to lead to significant differences in solid-state structures of the resulting materials. We illustrate this by comparing the structures of new multi-component crystals involving the model pharmaceutical ingredient caffeine and perfluorosuccinic or perfluoroadipic acid with the structures of analogous crystals based on the hydrocarbon diacids. Unlike hydrocarbon-based succinic and adipic acids which provide structurally similar hydrogen-bonded cocrystals and inclusion hosts with caffeine, perfluorosuccinic acid provides a salt and perfluoroadipic acid yields a cocrystal. Combined crystal structure analysis, solid-state and solution NMR analysis, single molecule conformational analysis and calculations of acid dissociation energies indicate that the different solid-state behavior of perfluoro- and hydrocarbon acids towards caffeine can be interpreted as a result of their distinct conformational properties rather than differences in pKa values.

We demonstrate that blending fluorinated molecules in PEDOT:PSS hole transport layers (HTL) induces charge transfers which impact on both charge extraction and photogeneration within organic photovoltaic (OPV) devices. OPVs fabricated with modified HTL and two photoactive
polymer blends led systematically to power conversion efficiencies (PCE) increases, with PTB7:PC70BM blend exhibiting PCE of ~ 8.3 %, i.e. ~ 15 % increase compared to pristine HTL devices. A reduced device-to-device characteristics variations was also noticed when fluorinated additives were used to modify the PEDOT:PSS. Shading lights onto the effect of HTL fluorination, we show that the morphology of the polymer:PCBM blends remains surprisingly unaffected by the fluorinated HTL surface energy but that, instead, the OPVs are impacted not only by the HTL electronic properties (work function, dipole layer, open circuit voltage, charge transfer dynamic) but also by alteration of the complex refractive indices (photogeneration, short circuit current density, external quantum efficiencies, electro-optic modelling). Both mechanisms find their origin in fluorination induced charge transfers. This work points towards fluorination as a promising strategy toward combining both external quantum efficiency modulation and power conversion efficiency enhancement in OPVs. Charge transfers could also be used more broadly to tune the optical constants and electric field distribution, as well as to reduce interfacial charge recombinations within OPVs.

The chemical vapor deposition method for fluorine-containing carbon materials preparation provided.  The claimed method comprises treating of carbons with fluorocarbons or derivatives that passes at a moderate high temperature. The fluorine-containing carbon materials show hydrophobicity, high thermal stability and can be used as catalysts support, lithium battery anodes, and hydrophobic materials or as surface precursor. Surface fluorine characterized by intensive signal in the XPS spectrum, found in a range of 685–687 eV. Obtained fluoro-containing functionalities is stable at a temperature about 1000 °C.

Superhydrophobic conductive carbon blacks were prepared by covalent bonding of perfluorocarbon and perfluoropolyether chains on the conductive carbon black surface. Perfluorodiacyl and perfluoropolyether peroxides were used as reagents for the chemical treatment. Their thermal decomposition produced respectively, perfluoroalkyl and perfluoropolyether radicals that directly bonded the polycyclic aromatic structure of carbon black surface. Measurements of contact angles with water on molded pellets made with carbon black powder demonstrated that water droplets were enduringly stable on the treated carbon blacks. Contact angle values were significantly high, exceeding the superhydrophobicity threshold. On the contrary, the droplets were adsorbed in few seconds by the native carbon black. Conductivity measurements showed that the covalent linkage of fluorinated chains weakly modified the electrical properties of the conductive carbon black, even if the surface properties changed so deeply. The relationship between the linkage of fluorinated chains and the variations of physical–chemical properties were studied combining electron spectroscopy, resistivity measurements, X-ray diffraction, scanning electron microscopy, surface area analysis and thermal gravimetric analysis. The superhydrophobic conductive carbon blacks were compared with a superhydrophobic carbon black obtained by direct fluorination of conductive carbon black with elemental fluorine, F2.