Fluoroalcohols as solvents for aliphatic polyamides

Some fluoroalcohols have been prepared by free-radical addition of methanol, ethanol and isopropanol to fluoroolefins as C₃F₆, CFHCFCF₃, (CF₃)₂CFCFCFCF₃, H(CF₂)₄CFCF₂, The general reaction is (1) R_fCFCF₂ + RR′CHOH = R_fCFHCF₂CRR′OH where R_f is a fluoroalkyl group, R and R′ are H or CH₃. NMR data of these alcohols are reported. 2,2,3,4,4,4-hexafluorobutanol (HFB) shows the best solvent ability among the compounds of this class. Its properties and solvent power have been evaluated and compared to the ones of trifluoroethanol (TFE) and hexafluoroisopropanol (HFIP). Some toxicological data related to HFB, TFE and HFIP are also reported.Owing to their strong tendency to form hydrogen bonds, fluoroalcohols are excellent solvents for polymeric materials which possess receptive sites for hydrogen bonding formation. The bonding power of the OH has been investigated by IR and NMR Spectroscopy on amide-group containing substrates. The properties and the correlations observed have pointed out that HFB may be usefully used as solvent for some aliphatic polyamides as Nylon 6.The polymer-solvent system Nylon 6-HFB has been studied and the constants of Mark-Houwink equation determined.     

Polymer radicals trapped in radical-initiated polytetrafluoroethylene

The electron spin resonance (ESR) spectra of polymer radicals found to be trapped in polytetrafluoroethylene (PTFE) polymerized with radical initiators were comparatively examined under various conditions and assigned. They are identified as the primary (propagating) radicals RCF₂CF₂·, which are transformed to primary peroxy radicals RCF₂CF₂OO· in the atmosphere. Studies of the rates of polymerization and postpolymerization and ESR measurements indicate that the radical content steadily increases during polymerization. The results are discussed in connection with the mechanism of polymerization of tetrafluoroethylene (TFE) and the unusual thermal stability of these radicals in PTFE prepared with initiator.     

Enthalpies of formation of radicals and the mass spectra of the products of tetrafluoroethylene polymerization in acetone

The mass spectra of the dissociative electron-impact ionization products of telomers formed upon the radiation-chemical telomerization of tetrafluoroethylene in acetone were measured over the range of m/z from 1 to 204. The most intense bands at m/z = 43, 51, and 57 were attributed to the CH₃CO⁺, CF₂H⁺ and CH₃COCH₂⁺ cations—the main dissociation products of the H(C₂F₄) _n CH₂COCH₃ telomers. The telomer composition was consistent with a radical telomerization mechanism, in which chain growth and chain transfer are due to the formation of the CH₃COCH₂^· radical. Based on published data supplemented with quantum-chemical calculations, the enthalpies of formation of the radicals R(CF₂) _n (n = 2–8; R = H, CH₃, CH₃CO, and CH₃COCH₂) were tabulated. The formation of telomers with the same terminal groups is consistent with thermodynamic data and a polymerization mechanism in which the chain growth reaction is diffusion-limited and the chain transfer reaction is activated hydrogen-atom transfer.     

ESR study of the structure and reactivity of spin-adducts of element- and metal-centered radicals with perfluorinated α-triketones

The addition of element-centered radicals to perfluorinated α-triketones (CF₃)₂CFCOCOCOC₂F₅ (1) and (CF₃)₂CFCOCOCO(CF₃)₂ (2) was studied by the ESR method. In the case of Si-centered radicals, α-siloxydiketomethyl radicals are formed, which are characterized by the highest delocalization of an unpaired electron. The dimerization of these radicals is characterized by a low value of the enthalpy of the radical—dimer equilibrium (2.7 kcal mol⁻¹). The Ge(C₆F₅)₃ and ·Mn(CO)₅ radicals are added to1 at the carbonyl group directly bound to the pentafluoroethyl substituent. The hindered rotation of the (CF₃)₂CF group was observed for the spin-adduct of ·Ge(C₆F₅)₃ with2. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 474–477, March, 1999.     

Tetrafluoroethylene telomerization using dibromohaloethanes as telogens

Carrier mediated telomerization (CMT) between C₂F₄ and bromochlorofluoroethanes has been evaluated in terms of product distributions arising from CMT and ‘normal’ telomerization. The effect of parameters like type of initiator and telogen, TFE pressure and temperature on the reaction has been studied. The peroxide initiated telomerization between dibromohaloethanes and C₂F₄ offers an easy synthetic route to α,ω-dibromo perfluoroalkanes Br(CF₂)_nBr with n = 2, 4, 6 and 8. The selectivity of the CMT products versus those from “normal” telomerization depends mainly on the choice of telogen and on its ability to act as ‘bromine donor’ in the radical telomerization. These perfluoroalkyl dibromides are useful intermediates for other derivatives, for example, perfluorinated mono- and diolefins, Br(CF₂)_nCHCH₂ and CH₂CH(CF₂)_nCHCH₂.     

ESR‐Vis/NIR Spectroelectrochemical Study of C70(CF3)2−. and C70(C2F5)2−. Radical Anions

A spectroelectrochemical study of the two isostructural asymmetric perfluoroalkyl derivatives C₁‐7,24‐C₇₀(CF₃)₂ and C₁‐7,24‐C₇₀(C₂F₅)₂ is presented. Reversible formation of their stable monoanion radicals is monitored by cyclic voltammetry and by in situ ESR‐Vis‐NIR spectroelectrochemistry. The ESR spectrum of the C₇₀(CF₃)₂^?. radical is a 1:3:3:1 quartet with a ¹⁹F hyperfine coupling constant (a(F)) of 0.323(4) G, demonstrating that the unpaired spin is coupled to only one of the two CF₃ groups. The ¹³C satellites are assigned to specific carbon atoms. The ESR spectrum of the C₇₀(C₂F₅)₂^?. radical is an apparent octet with an apparent a(F) value of 0.83(2) G. DFT calculations suggest that this pattern is due to the superposition of spectra for four nearly isoenergetic C₇₀(C₂F₅)₂^?. conformers. Time‐dependent DFT calculations suggest that the NIR band at 1090 nm exhibited by both C₇₀(R_f)₂^?. radical anions is assigned to the SOMO→LUMO+3 transition. The analogous NIR band exhibited by the closed‐shell C₇₀(CF₃)₂^2? dianion was blue‐shifted to 1000 nm.     

Chair‐ and Boat‐Configurations of Silver(I) Complexes of Ditopic Ligand Involving Benzimidazolyl Substituents

The ditopic ligand 1, 2‐bis(benzimidazol‐1‐ylmethyl)benzene (L¹) as well as its silver(I) complexes [Ag₂L¹₂(CF₃CO₂)₂] ( 1 ) and [Ag₂L¹₂](CF₃SO₃)₂ · (L¹) · 2H₂O · 0.5C₂H₅OH ( 2 ) were prepared and structures characterized by X‐ray crystallography. The Ag^I atoms in 1 are trigonally coordinated by two N_BIm atoms from the arms of L¹ and by one O atom of the anion CF₃CO₂^—, while those in 2 are only linearly ligated by N_BIm. Different silver salts of CF₃CO₂^— and CF₃SO₃^— lead to different configurations of the dimeric unit [Ag₂L¹₂]²⁺: chair‐form in ( 1 ) but boat‐form in ( 2 ). The discrete molecules in both 1 and 2 are assembled into network structures through face‐to‐face π · · · π stacking and edge‐to‐face C—H · · · π interactions in the crystalline state, as well as N—H · · · O and C—H · · · O hydrogen bonds. Solution ¹H NMR studies showed the formation of one sole species in solution or a rapid equilibrium was established on the NMR time scale at room temperature.     

Postradiation polymerization of tetrafluoroethylene on mineral supports at low temperatures

The low-temperature graft polymerization of tetrafluoroethylene (TFE) on mineral supports (SiO₂, Al₂O₃, TiO₂, and activated charcoal) has been investigated by the microcalorimetry, ESR, and IR spectroscopy techniques. It has been shown that polymerization of TFE is initiated by radical ion centers formed upon radiolysis of the support. The initiation stage includes the interaction of a radical ion particle of the support with a monomer molecule yielding a growing neutral radical. The radical growth of polymer chains has been confirmed by the appearnce of the ESR spectrum of terminal fluoroalkyl radicals ～CF₂?CF₂, and the covalent C-Si bonds of the polymer with the support have been detected by means of IR spectroscopy. The efficiency of the low-temperature graft polymerization depends on the monomer sorption and the sorbent nature: the highest efficiency is observed for Al₂O₃ and, then, macroporous glasses; grafting proceeds to the least extent (yield below 5%) on the carbon supports, which do not the form radical ion centers during radiation activation.     

Rapid intramolecular interactions between organic isocyanates and hexafluorobut-2-yne on a dirhodium centre; X-ray crystal structure of (η-C5H5)2Rh2 {μ2(η3-C(CF3)C(CF3)C(O)N(Ph)}

Complexes of formula (η-C₅H₅₂Rh₂{CF₃C₂CF₃ · RNCO} have been prepared by three methods, from reactions between organic isocyanates and (η-C₅H₅)₂Rh₂(CO)(CF₃C₂CF₃) or (η-C₅H₅)₂Rh₂(CO)₂(CF₃C₂CF₃); by treatment of (η-C₅H₅)₂Rh₂(CO)(CF₃C₂CF₃) with organic azides; and by oxidation with Me₃NO of the organic isocyanide in (η-C₅H₅)₂Rh₂(CO)(CNR)(CF₃C₂CF₃). The crystal and molecular structure of the complex (η-C₅H₅)₂Rh₂{CF₃C₂CF₃ · RNCO} with R = Ph has been determined from single crystal X-ray diffraction data. This reveals that the isocyanate has condensed with the hexafluorobut-2-yne to form an amide ligand of the form C(CF₃)C(CF₃)C(=O)N(R); this bridges the two rhodium atoms in a μ₂η³-manner.     

The kinetics of the addition of alkyl radicals to carbonyl groups. Part I. The addition of methyl radicals to hexafluoroacetone in the gas phase. The formation of the hexafluoro-t-butoxy radical

By pyrolyzing di-t-butyl peroxide over the temperature range of 405–450 K in the presence of hexafluoroacetone the kinetics of the addition reaction (1), CH₃ + (CF₃)₂CO→; (CF₃)₂C(?)CH₃, have been studied. Detailed analyses have shown that the principal product of the adduct radical, (CF₃)₂C(?)CH₃, is CF₃COCH₃ from reaction (2), (CF₃)₂C(?)CH₃ → CF₃COCH₃ + CF₃. The rate constant of the addition reaction was determined to be k₁(dm³/mol·s) = (1.1 ± 4.0) + 10⁹ exp(-(3680 ± 480)/T) over the temperature range 405–450 K, based on the value k₃ = 2.2 × 10¹⁰ dm³/mol·s for reaction (3), 2CH₃ → C₂H₆. The results are discussed in relation to existing data for radical additions to carbonyl groups.     

Kinetics and mechanism of radiation telomerization of tetrafluoroethylene in hexafluoropropan-2-ol and trifluoroethanol

The kinetics of radiation telomerization of tetrafluoroethylene (TFE) in trifluoroethanol and hexafluoropropan-2-ol (HFIP) has been investigated by method of kinetic calorimetry. The nature of active centers initiating the process of telomerization of tetrafluoroethylene in hexafluoroisopropanol in the temperature range of 77—300 K was investigated by ESR spectroscopy. The molecular structure and properties of the obtained telomeres were studied by IR spectroscopy and TGA.     

Mechanism of thermal decomposition of peroxide radicals formed in polytetrafluoroethylene by γ-ray irradiation

Thermal decomposition of polymer peroxide radicals formed in γ-irradiated polytetrafluoroethylene, ～CF₂CF(OO·)CF₂～ (radical I) and ～CF₂CF₂(OO～) (radical II), was studied by mass spectral analysis of the gas evolved in comparison with their photolysis with ultraviolet light. In the thermal decomposition of radicals I and II, CO₂ was the most abundant component, with smaller amount of CO, CF₂O, and gases present. In the photolysis, CO instead of CO₂ was the most abundant in the case of radical I, while in the case of radical II, CO₂ was again the main product. When a labeled polymer peroxide radical, ～CF₂CF(¹⁸O-¹⁸O·)CF₂～, was treated with heat or ultraviolet light, C¹⁸O¹⁶O was detected as a main component. In the treatment with ultraviolet light, a large amount of C¹⁸O comparable to that of C¹⁸O¹⁶O was also obtained. The mechanism of main-chain scission of radicals I and II is discussed.     

Metallocene and Organo-main Group Trifluoromethanesulfonates

The substituted metallocene compounds Cp₂M(OSO₂CF₃)₂ (Cp=η⁵-C₅H₅; M = Ti, Zr, Hf, Nb, Mo), CpTi(OSO₂CF₃)₃ · 0.75(1,2-dimethoxyethane), and the organo-main group compounds (C₆H₅)₃M′(OSO₂CF₃) (M′=Si, Ge), (C₆H₅)₂Sn(OSO₂CF₃)₂ and (C₆H₅)₃Sb(OSO₂CF₃)₂, were synthesized from the corresponding chloride or bromide compounds and silver trifluoromethanesulfonate (triflate) and characterized spectroscopically, including a detailed analysis of their IR spectra. Triflate coordination is typically monodentate, but CpTi(OSO₂CF₃)₃ · 0.75(1,2-dimethoxyethane) and the organo-germanium triflate show evidence of bidentate CF₃SO ₃⁻ ligands and are likely to have polymeric structures. Conductance measurements in nitromethane, acetone and acetonitrile have demonstrated the ease of triflate substitution, with a limited kinetic study of acetone solvation of the Ti and Hf compounds supporting an associative pathway. Three new catalysts for the polymerization of tetrahydrofuran, Cp₂HfCl₂/Ag(OSO₂CF₃), CpTiCl₃/Ag(OSO₂CF₃) and (C₆H₅)₂SiCl₂/Ag(OSO₂CF₃), are also reported.     

Mechanism and kinetics of the reaction of F with trivalent phosphorus iodide using electron spin resonance detection

The reaction of iodobistrifluoromethylphosphine, P(CF₃)₂I, with atomic fluorine was studied by fast-flow ESR methods. The initial stage of the reaction is the abstraction of I by F, to form IF with a bimolecular rate constant of (1.0 ± 0.3) × 10¹⁴ cm³ mol^?1 s^?1 at 297 K. In the presence of excess F, stepwise addition to the phosphorous occurs. In the presence of excess P(CF₃)₂I, the reaction P(CF₃)₂ + IF → P (CF₃)₂F + I appears to take place. This reaction rate is slow relative to P(CF₃)₂ + F → P(CF₃)₂F.     

Theoretical evaluation of the nature and strength of the F������F intermolecular interactions present in fluorinated hydrocarbons

The nature, strength and directionality of C?CF···F interactions were theoretically evaluated on all symmetry unique dimers present in the CF₄, C₂F₄ and C₆F₆ crystals and on CF₄, CHF₃, CH₂F₂ and CH₃F model dimers placed in two different geometries. On each dimer, the interaction energy was computed at the MP2/aug-cc-pVDZ level, and also an Atoms in Molecule analysis of the dimer electron density was done to find all intermolecular bonds. The characterization was completed by computing the energy components of the dimer interaction energy, using the SAPT method. The results show that in most dimers found in the CF₄, C₂F₄ and C₆F₆ crystals, there are more than one C?CF···F intermolecular bond and sometimes even a C?CF···?? intermolecular bond. By selecting dimers presenting one C?CF···F bond, the following strength can be estimated for a single C?CF···F bond: ?0.21?kcal/mol in C(sp³) atoms, ?0.25?kcal/mol in C(non-aromatic sp²), ?0.41?kcal/mol in C(aromatic sp²). The interaction energy of the dimer grows almost linearly with the number of C?CF···F bonds present. The relative orientation of the C?CF···F bond affects the bond strength. The SAPT calculations indicate that in collinear dimers, C?CF···F interactions are strongly dominated by the dispersion energetic component, while when in non-collinear conformations the electrostatic component can be as important as the dispersion one.     

Fluoroborates by Cleavage of Trimethylamine‐bis(trifluoromethyl)boranes with NEt3 × 3 HF. Structures of C6F5(CF3)2B · NMe3, K[C6H5CH2(CF3)2BF], and K[C6H5(CF3)2BF]

Trimethylamine‐bis(trifluoromethyl)boranes R(CF₃)₂B · NMe₃ (R = cis/trans‐CF₃CF=CF ( 1/2 ), HC≡C ( 3 ), H₂C=CH ( 4 ), C₂H₅ ( 5 ), C₆H₅CH₂ ( 6 ), C₆F₅ ( 7 ), C₆H₅ ( 8 )) react with NEt₃ × 3 HF depending on the nature of R at 155–200 °C under replacement of the trimethylamine ligand to form the corresponding fluoro‐bis(trifluoromethyl)borates [R(CF₃)₂BF]^– ( 1 a/2 a – 8 a ). The structures of 7 , K[C₆H₅CH₂(CF₃)₂BF] ( K‐6 a ), and K[C₆H₅(CF₃)₂BF] ( K‐8 a ) have been investigated by single‐crystal X‐ray diffraction. In 7 the CF₃ groups make short repulsive contacts with NMe₃ and C₆F₅ entities – the B–CF₃ bonds being unusually long. The B–F bond lengths of K‐6 a and K‐8 a (1.446(3) and 1.452(2) Å, respectively) are long for a fluoroborate.     

Rate constants for addition of the OP·(OPri)2, Me3C·, and Me(CH2)3 ·CH2 radicals to methano[60]fullerenes C60CX1X2 (X1 = X2 = CO2Et; X1 = CO2Me,X2 = OP(OMe)2; X1 = X2 = OP(OEt)2)

The rate constants for the addition of the OP^·(OPrⁱ)₂, Me₃C^·, and Me(CH₂)₃ ^·CH₂ radicals to the methano[60]fullerenes C₆₀CX¹X² (X¹ = X² = CO₂Et; X¹ = CO₂Me, X² = OP(OMe)2; X¹ = X² = OP(OEt)₂) were determined by ESR spectroscopy. Methanofullerenes are more reactive toward these radicals than C₆₀ fullerene.     

Synthesis of new functionalized 5,5-dimethyl-1-pyrroline 1-oxides and their investigation as spin traps

The reactions of 5,5-dimethyl-3-oxo-1-pyrroline 1-oxide (3-oxo-DMPO, 1) with NH₂OH and N₂H₄ afforded oxime (2a) and hydrazone (2b), respectively. The reaction products were studied as spin traps for the short-lived radicals HO^·, Ph^·, PhCO₂ ^·, NC(Me₂)C^·, and NC(Me₂)CO^·. The nitroxides generated in the reactions of the above-mentioned short-lived radicals with nitrones 1 and 2a,b were characterized by ESR spectroscopy. Of these nitrones, oxime 2a is the most effective radical trap.     

2,4‐Diamino‐6‐methyl‐1,3,5‐triazin‐1‐ium trifluoroacetate

Crystals of the title compound, C₄H₈N₅⁺·C₂F₃O₂⁻, are built up of singly protonated 2,4‐diamino‐6‐methyl‐1,3,5‐triazin‐1‐ium cations and trifluoroacetate anions. The CF₃ group of the anion is disordered. The oppositely charged ions interact via almost linear N—H...O hydrogen bonds, forming a CF₃COO⁻...C₄H₈N₅⁺ unit. Two units related by an inversion centre interact through a pair of N—H...N hydrogen bonds, forming planar (CF₃COO⁻...C₄H₈N₅⁺...C₄H₈N₅⁺·CF₃COO⁻) aggregates that are linked by a pair of N—H...O hydrogen bonds into chains running along the c axis.     

Radiation polymerization and copolymerization of fluorinated acrylates and methacrylates induced by γ-rays

Fluorinated acrylates and methacrylates radiolyzed at 77 K polymerize upon heating in the range from the glass-transition to the melting temperature. In the case of acrylates, the temperature range of postradiation polymerization increases by more than 100 K with the increasing chain length of the perfluorinated substituent from C₂F₄ to C₈F₁₇. The introduction of perfluorinated substituents into methacrylate molecules makes it possible to obtain them in the glassy state and to carry out low-temperature postradiation polymerization, in contrast to their hydrocarbon analogues. The termination rate constant of the polymerization of fluorinated methacrylates has a lower value as compared to conventional methacrylates. The formation of crosslinked structures is suppressed during the copolymerization of fluorinated acrylates with methacrylates. The ESR spectra of growing polymer radicals of fluorinated acrylic ∼CH₂C^·H(COOCH₂C₆F₁₃)∼ and methacrylic CH₂C^·(CH₃)(COOCH₂C₂F₄H)∼ monomers have been identified.