Hexafluoroacetone Hydrate Research Articles

Semi-fluorinated (6F) polyaryl ethers and polyphenylenes via interfacial electrophilic condensation polymerization with hexafluoroacetone hydrate

A series of semi-fluorinated polymers were obtained by Friedel-Crafts polymerization of hexafluoroacetone trihydrate (HFAH) with a variety of activated and non-activated aromatic monomers. Interfacial (water/dichloroethane) electrophilic aromatic substitution (EAS) polymerizations were carried out with trifluoromethanesulfonic anhydride (Tf2O) and Aliquat® 336 as phase transfer catalyst. This versatile and straightforward method achieved the synthesis of moderate to high molecular weight (12.0–29.6 kDa) polyaryl ethers and polyphenylenes with 1,1,1,3,3,3-hexafluoroisopropylene (6F) main chain linkages. Predominantly amorphous film-forming materials were obtained with low branching, high solubilities in common organic solvents, thermo-oxidative stabilities up to 500 °C, and glass transitions (Tg) ranging from 157 to 250 °C. The optical and dielectric properties of these materials were also studied from which high visible region transmittance and low dielectric constant values comparable with commercial materials were found.

Teaching Old Polymers New Tricks: Improved Synthesis and Anomalous Crystallinity for a Lost Semi‐Fluorinated Polyaryl Ether via Interfacial Polymerization of Hexafluoroacetone Hydrate and Diphenyl Ether

Front Cover: Article 2200737 by Dennis W. Smith, Jr. and co-workers highlights the versatile and scalable electrophilic synthesis of a forgotten semi-fluorinated polyaryl ether from diphenyl ether and hexafluoroacetone hydrate catalyzed by triflic acid. Despite the presence of 6F linkages, anomalous crystallinity is observed for the very first time for this polymer. This interfacial electrophilic aromatic polymerization is applicable to other activated aromatics.

Teaching Old Polymers New Tricks: Improved Synthesis and Anomalous Crystallinity for a Lost Semi-Fluorinated Polyaryl Ether via Interfacial Polymerization of Hexafluoroacetone Hydrate and Diphenyl Ether.

A practical and direct electrophilic polymerization of hexafluoroacetone hydrate with diphenyl ether toward the preparation of semi-fluorinated polyaryl ethers (PAE) is reported. Electrophilic aromatic substitution (EAS) polymerization under interfacial conditions with phase transfer catalyst (Aliquat 336) proceeds in trifluoromethanesulfonic anhydride by generation of trifluoromethanesulfonic acid and the protonated hexafluoroacetone (HFA) in situ affording 1,1,1,3,3,3-hexafluoroisopropylidene (6F) PAE with high regioselectivity (4,4'-DPE) and high molecular weight (≈60kDa). Although first reported in a 1966 US Patent by DuPont using harsh conditions, improved synthetic methods or modern characterization has not been disclosed until now. Despite the presence of the 6F group, known to impart disordered morphology, this simple semi-fluorinated PAE exhibits anomalous crystallinity with polymorphic melting points (Tm ) ranging from 230-309°C, high solubility in common organic solvents, a glass transition (Tg ) of 163°C, and thermo-oxidative stability above 500°C. Tough optically clear films prepared from solution give transmittance higher than 90% throughout the visible region. Synthesis, mechanistic aspects, and characterization including surface and dielectric properties are discussed.

Photoredox-Catalyzed Deoxygenation of Hexafluoroacetone Hydrate Enables Hydroxypolyfluoroalkylation of Alkenes.

An unprecedented photoredox-catalyzed phosphine-mediated deoxygenation of hexafluoroacetone hydrate was established to accomplish the hydroxylpolyfluoroalkylation of electron-deficient alkenes. A range of bis(trifluoromethyl)carbinols were facilely accessed by using readily available hexafluoroacetone hydrate, instead of toxic gaseous hexafluoroacetone. A range of electron-deficient alkenes are tolerated, giving the corresponding hydro-hydroxylpolyfluoroalkylated products in moderate to high yields. Remarkable features of this synthetic strategy include operational simplicity, mild reaction conditions, excellent regioselectivity, and broad functional group tolerance. The success of this strategy relies on the delicate utilization of aldehyde/ketone-gem-diol intrinsic equilibrium, which offers an innovated open-shell pathway for the assembly of synthetically challenging polyfluoroalkylated scaffolds.

Photoredox‐Catalyzed Deoxygenation of Hexafluoroacetone Hydrate Enables Hydroxypolyfluoroalkylation of Alkenes

AbstractAn unprecedented photoredox‐catalyzed phosphine‐mediated deoxygenation of hexafluoroacetone hydrate was established to accomplish the hydroxylpolyfluoroalkylation of electron‐deficient alkenes. A range of bis(trifluoromethyl)carbinols were facilely accessed by using readily available hexafluoroacetone hydrate, instead of toxic gaseous hexafluoroacetone. A range of electron‐deficient alkenes are tolerated, giving the corresponding hydro‐hydroxylpolyfluoroalkylated products in moderate to high yields. Remarkable features of this synthetic strategy include operational simplicity, mild reaction conditions, excellent regioselectivity, and broad functional group tolerance. The success of this strategy relies on the delicate utilization of aldehyde/ketone‐gem‐diol intrinsic equilibrium, which offers an innovated open‐shell pathway for the assembly of synthetically challenging polyfluoroalkylated scaffolds.

Hydrophobicity/hydrophilicity control for SiO2-based aerogels: The role of a supercritical solvent

Effect of solvent used as a supercritical fluid during the synthesis of SiO2-based aerogels on their structure and hydrophobicity/hydrophilicity was studied. The use of different solvents allows varying water contact angle in the range from 0° to 142°. The use of hexafluoroisopropanol as supercritical fluid leads to preparation of hydrophobic aerogels containing considerable amount of chemically bound fluorine. The use of hexafluoroacetone hydrate as a co-solvent during the synthesis of SiO2 lyogels provides preparation of hydrophobic aerogels with high specific surface areas.

Hexafluoroacetone: A new solvent for manufacturing SiO2-based aerogels

Hexafluoroacetone (HFA) hydrate has been shown to appreciably influence the physicochemical parameters of SiO2 aerogels when used at the stage of preparing hydrated silica gels in the synthesis of the aerogels. For example, when [SiO2]: HFA = 1: 2 in the reaction mixture, aerogels have specific surface areas about 1.5 times as high as in similar samples prepared without HFA. Aerogel samples prepared in the presence of HFA contain considerable amounts of chemically bound fluorine.

Nucleophilic Trifluoromethylation of Carbonyl Compounds: Trifluoroacetaldehyde Hydrate as a Trifluoromethyl Source

A feasible nucleophilic trifluoromethylating protocol has been developed using trifluoroacetaldehyde hydrate as an atom-economical trifluoromethyl source. The reaction was found to be applicable to the nucleophilic trifluoromethylation of a broad spectrum of carbonyl compounds with satisfactory yields in general. DFT calculations have been performed to provide mechanistic insight into the present and related reactions employing 2,2,2-trifluoro-1-methoxyethanol and hexafluoroacetone hydrate.

Amidinate Salt of Hexafluoroacetone Hydrate for the Preparation of Fluorinated Compounds by the Release of Trifluoroacetate

A powerful, new reagent, an amidinate salt of hexafluoroacetone hydrate, is an air-stable salt that can be used for the preparation of fluorinated organic molecules. Nucleophilic trifluoromethylation reactions are demonstrated following the base-promoted release of trifluoroacetate. This reagent is soluble in many polar organic solvents and produces fluoroform, following the release of trifluoroacetate. Reactions with this reagent and common electrophiles provide excellent yields of trifluoromethylated products.

First synthesis of the N(1)-bulky substituted imidazole 3-oxides and their complexation with hexafluoroacetone hydrate

Synthesis of new 2-unsubstituted imidazole 3-oxides bearing bulky substituents at the N(1) atom, based on the condensation of appropriate alkylamines, formaldehyde, and corresponding α- (hydroxyimino)ketone, is described. Treatment of imidazole 3-oxides with hexafluoroacetone hydrate (HFAH) yields crystalline 1:1 complexes in nearly quantitative yields. Heating of isolated complexes possessing phenyl ring at the C(4) atom of imidazole ring, results in their isomerization into imidazol-2-ones in fair yields. The formation of analogous complexes of HFAH with other azole N-oxides is also described.

Reactions of 2-Unsubstituted 1H-Imidazole 3-Oxides with 2,2-Bis(trifluoromethyl)ethene-1,1-dicarbonitrile: A Stepwise 1,3-Dipolar Cycloaddition

The reaction of 1,4,5-trisubstituted 1H-imidazole-3-oxides 1 with 2,2-bis(trifluoromethyl)ethene-1,1-dicarbonitrile (7, BTF) yielded the corresponding 1,3-dihydro-2H-imidazol-2-ones 10 and 2-(1,3-dihydro- 2H-imidazol-2-ylidene)malononitriles 11, respectively, depending on the solvent used. In one example, a 1 : 1 complex, 12, of the 1H-imidazole 3-oxide and hexafluoroacetone hydrate was isolated as a second product. The formation of the products is explained by a stepwise 1,3-dipolar cycloaddition and subsequent fragmentation. The structures of 11d and 12 were established by X-ray crystallography.

Synthesis of Novel Lipophilic and/or Fluorophilic Ethers of Perfluoro‐tert‐butyl Alcohol, Perfluoropinacol and Hexafluoroacetone Hydrate via a Mitsunobu Reaction: Typical Cases of Ideal Product Separation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of novel lipophilic and/or fluorophilic ethers of perfluoro- tert-butyl alcohol, perfluoropinacol and hexafluoroacetone hydrate via a Mitsunobu reaction: Typical cases of ideal product separation

Fluorophilic ethers having the structure RC(CF 3) 2O(CH 2) 3C n F 2 n + 1 are obtained in high yields, when F- tert-butyl alcohol (R = CF 3), F-acetone hydrate (R = O(CH 2) 3C n F 2 n + 1 ), F-pinacol (R = C(CF 3) 2O(CH 2) 3C n F 2 n + 1 ) are reacted with 3-perfluoroalkyl-1-propanols (C n F 2 n + 1 (CH 2) 3OH, n = 4, 6, 8, 10) in a Mitsunobu reaction (Ph 3P/DIAD [ i-PrO 2CN = NCO 2Pr- i]/ether). The parent lipophilic ethers with the structure of (CF 3) 3CO(CH 2) 3C n H 2 n + 1 were prepared analogously using the corresponding fatty alcohols and F- tert-butyl alcohol. To achieve ideal separations, products were transferred to orthogonal phases relative to the other reaction components using fluorous extraction, fluorous solid–organic liquid filtration, or steam-distillation. Selected physical properties including melting and boiling point, together with fluorous partition coefficients of these ethers were determined and the figures obtained were qualitatively analyzed using relevant thermodynamic theories. Some of these ethers are liquids with rather low freezing points and are miscible with fluorocarbon solvents.

Embedded Mn-Porphyrins in PDMS and ORMOSILs as Effective Catalysts for Cyclooctene Epoxidation by H2O2 in Supercritical Carbon Dioxide

The heterogeneous oxidation of cyclooctene with H2O2 catalyzed by Mnporphyrins embedded in polydimethylsiloxane (PDMS) and organically modified silicates (ORMOSILs), in the presence of hexafluoroacetone hydrate (HFAH) as cocatalyst, has been studied in supercritical carbon dioxide (scCO2) at 40°C and 20 MPa. Complete olefin conversion may be obtained with the formation of cyclooctene oxide as sole product, employing molar ratios of Mn-porphyrin/Substrate/H2O2 of 1:400:2000. Keywords: carbon dioxide, hexafluoroacetone, hydrogen peroxide, oxidation, porphyrin

Catalytic Olefin Epoxidation With H2O2 in Supercritical CO2. Synergic Effect by Hexafluoroacetone and Manganese-Porphyrins

The heterogeneous oxidation of cyclooctene with hydrogen peroxide catalyzed by manganese 5,10,15,20-tetrakis(2′,6′-dichlorophenyl)porphyrinate, in the presence of hexafluoroacetone hydrate as co-catalyst, has been studied in supercritical carbon dioxide, at 40 °C and 20 MPa. Under proper conditions, a complete olefin conversion may be obtained with the formation of cyclooctene oxide as the sole product. Fixation by hexafluoroacetone into its perhydrate derivatives provides a useful system to solubilize hydrogen peroxide in supercritical carbon dioxide, and to hamper catalyst bleaching and oxidant decomposition. Moreover, in the presence of both manganese-porphyrin and hexafluoroacetone, the reaction rates are enhanced. Among the factors that may increase yields and rate of conversion, the use of a Teflon-coated steel reactor rather than an uncoated one proved to be quite relevant, thus indicating the occurrence of a parasite radical decomposition of hydrogen peroxide promoted by steel reactor walls.

Artificial Spinning and Characterization of Silk Fiber from Bombyx mori Silk Fibroin in Hexafluoroacetone Hydrate

Artificial Spinning and Characterization of Silk Fiber from <i>Bombyx </i><i>m</i><i>ori</i> Silk Fibroin in Hexafluoroacetone Hydrate

Highly efficient cascade-oxygen-transfer from H 2O 2 to olefins mediated by halogenated carbonyl compounds and metalloporphyrins

The catalytic oxidation of cyclohexene with hydrogen peroxide promoted by manganese and iron porphyrins has been studied in the presence of halogenated carbonyl compounds as co-catalysts in a dichloromethane/water biphasic medium. The efficiency of the overall catalytic process is strictly related to the nature of the co-catalyst and to the high reactivity of its perhydrate form toward metalloporphyrins in forming an high valent oxo-pororphyrin derivative. Hydrogen peroxide fixation by hexafluoroacetone hydrate provides an useful system to hamper catalyst bleaching and/or oxidant decomposition. Thus, a complete olefin conversion into oxygenated products is accomplished with a very limited excess of oxidant respect to the organic substrate.

Fluoroalcohols as structure modifiers in peptides and proteins: hexafluoroacetone hydrate stabilizes a helical conformation of melittin at low pH.

The effect of hexafluoroacetone hydrate (HFA) on the structure of the honey bee venom peptide melittin has been investigated. In aqueous solution at low pH melittin is predominantly unstructured. Addition of HFA at pH approximately 2.0 induces a structural transition from the unstructured state to a predominantly helical conformation as suggested by intense diagnostic far UV CD bands. The structural transition is highly cooperative and complete at 3.6 M (50% v/v) HFA. A similar structural transition is also observed in 2,2,2 trifluoroethanol which is complete only at a cosolvent concentration of approximately 8 M. Temperature dependent CD experiments support a 'cold denaturation' of melittin at low concentrations of HFA, suggesting that selective solvation of peptide by HFA is mediated by hydrophobic interactions. NMR studies in 3.6 M HFA establish a well-defined helical structure of melittin at low pH, as suggested by the presence of strong NH/NHi+1 NOEs throughout the sequence, along with many medium range helical NOEs. Structure calculations using NOE-driven distance constraints reveal a well-ordered helical fold with a relatively flexible segment around residues T10-G11-T12. The helical structure of melittin obtained at 3.6 M HFA at low pH is similar to those determined in methanolic solution and perdeuterated dodecylphosphocholine micelles. HFA as a cosolvent facilitates helix formation even in the highly charged C-terminal segment.

Chain Flexibility Characterization of Poly(oxymethylene)

Flory's characteristic ratio C∞ for poly(oxymethylene) (POM) has been measured by Stockmayer from viscosity measurements in hexafluoroacetone sesquihydrate. The value of C∞ determined was 10.5. almost the same as that for polystyrene. This C∞ value was suspected of being higher than the real C∞ value of POM because of the strong solvation power of hexafluoroacetone hydrate and its specific interaction with POM. In this paper, the C∞ of POM were determined in m-cresol at 100°C and p-chlorophenol at 60°C via intrinsic viscosity measurements. Characteristic ratios of 6.72 and 6.97 were found at 60°C and 100°C, respectively. The results show that the POM chain is more flexible than polystyrene and is similar in flexibility to polyethylene chain. The positive temperature coefficient of chain dimensions indicates that more compact chain conformations have lower energies. The Mark-Houwink-Sakurada equations for POM in m-cresol (100°C) and p-chlorophenol (60°C) have been evaluated simultaneously.

Hexafluoroacetone hydrate as a structure modifier in proteins: characterization of a molten globule state of hen egg-white lysozyme.

A molten globule-like state of hen egg-white lysozyme has been characterized in 25% aqueous hexafluoroacetone hydrate (HFA) by CD, fluorescence, NMR, and H/D exchange experiments. The far UV CD spectra of lysozyme in 25% HFA supports retention of native-like secondary structure while the loss of near UV CD bands are indicative of the overall collapse of the tertiary structure. The intermediate state in 25% HFA exhibits an enhanced affinity towards the hydrophobic dye, ANS, and a native-like tryptophan fluorescence quenching. 1-D NMR spectra indicates loss of native-like tertiary fold as evident from the absence of ring current-shifted 1H resonances. CD, fluorescence, and NMR suggest that the transition from the native state to a molten globule state in 25% HFA is a cooperative process. A second structural transition from this compact molten globule-like state to an "open" helical state is observed at higher concentrations of HFA (> or = 50%). This transition is characterized by a dramatic loss of ANS binding with a concomitant increase in far UV CD bands. The thermal unfolding of the molten globule state in 25% HFA is sharply cooperative, indicating a predominant role of side-chain-side-chain interactions in the stability of the partially folded state. H/D exchange experiments yield higher protection factors for many of the backbone amide protons from the four alpha-helices along with the C-terminal 3(10) helix, whereas little or no protection is observed for most of the amide protons from the triple-stranded antiparallel beta-sheet domain. This equilibrium molten globule-like state of lysozyme in 25% HFA is remarkably similar to the molten globule state observed for alpha-lactalbumin and also with the molten globule state transiently observed in the kinetic refolding experiments of hen lysozyme. These results suggest that HFA may prove generally useful as a structure modifier in proteins.