Reactions of Methyl Perfluoroalkyl Ethers with Isopropyl Alcohol: Experimental and Theoretical Studies

The reaction of an isomeric mixture of the methyl perfluoroalkyl ether, C4F9OCH3 (Novec-7100), in the presence of isopropyl alcohol (IPA) and/or water has been studied by measuring the rate of product formation using an ion-selective electrode (ISE) for fluoride ion, Karl Fisher coulometric titrations for water, and 1H and 19F NMR spectroscopy for product identification and rate studies. The results showed the methyl perfluoroalkyl ether to be very stable with products forming at the rate of ∼1 ppm per year at a laboratory temperature of 20 °C. Measurements over the temperature range of 6° to 100 °C were made on samples aged for periods up to 1.8 years. Density functional theory calculations (DFT, B3LYP/6-31+G(d)) were employed to investigate different reaction pathways and formulate the probable reaction mechanism. The experimental enthalpy (ΔH⧧) and entropy (ΔS⧧) of activation were determined based on several different kinetic measurements. The ΔH⧧ values are in the range of 20–25 kcal/mol and the corresponding ΔS⧧ values range from −32 to −15 cal/(mol K). These are in good agreement with the theoretical values. While the range of ΔH⧧ values does not change appreciatively, the ΔS⧧ values are dependent on the proportion of vapor to liquid involved in the reaction of C4F9OCH3 with IPA so that the more vapor the more negative the ΔS⧧ value

Characterization by NMR of Reactants and Products of Hydrofluoroether Isomers, CF3(CF2)3OCH3 and (CF3)2C(F)CF2OCH3, Reacting with Isopropyl Alcohol

The 3M Company product Novec™ 71IPA DL, a mixture of methoxyperfluorobutane, methoxyperfluoroisobutane and 4.5 wt.% isopropyl alcohol, has been found to be very stable at ambient temperature, producing fluoride at the rate of ~1 ppm/year. Our earlier kinetic and theoretical studies have identified the reaction mechanism. This paper identifies the 1H and 19F NMR chemical shifts, multiplicities, and coupling constants of reactants and the major products that result from aging the mixture in sealed Pyrex NMR tubes for periods up to 1.8 years at temperatures from 26 °C to 102 °C. Chemical shifts and coupling constants of fluorine and hydrogen atoms on the hydrofluoroethers and isopropyl alcohol are traced through the reactions to their values in the products – esters, isopropylmethyl ether, and HF. These spectral positions, multiplicities, and coupling constants are presented in table format and as figures to clarify the transformations observed as the samples age

Addition Compounds of Phosphorus(V) Chloride and Aromatic Nitrogen Bases. Crystal Structure and 1H NMR and Raman Spectra of Pyrazine-Phosphorus(V) Chloride

It has been established that the compound of empirical formula Pels exhibits three coordination numbers dependent upon the physical state and choice of solvent. Two competing equilibria have recently been reported1 in ionizing solvents 2PC1, == PC1,\u27 + PCI,- PCI, t PCl,+ + C1- In the solid state, a metastable crystal modification has been found and proposed2 to incorporate chloride ions into the crystal lattice which would normally contain only PCh+ ions and PCbions

Activation of Two Carbon-Hydrogen Bonds of Nitromethane by a Dinuclear Gold(II) Ylide Complex. The Formation of a CHNO2-Bridged A-Frame Complex

The reaction of CH,NO, (neat) with the dinuclear gold(II) ylide complex Au2[(CH2)2PPh2]2(O2CPh)2 leads to the rupture of two C-H bonds and the formation of an A-frame species with a CHNO2 bridge. The X-ray molecular structure and the 500-MHz solution 1H NMR spectrum establish the formation of the species

Addition Compounds of Phosphorus(V) Chloride and Aromatic Nitrogen Bases. Crystal Structure and 1H NMR and Raman Spectra of Pyrazine-Phosphorus(V) Chloride

The solid-state structure of a nonionic adduct of phosphorus(V) chloride and pyrazine, C4H4N2-PCI5, shows phosphorus to be six-coordinate with one octahedral position occupied by a nitrogen atom of the pyrazine ring. The monoclinic crystal is of space group C2/c having four molecules per unit cell of dimensions a = 8.359 (8) A, b = 16.202 (15) A, c = 7.568 (7) A, and p = 99.37 (7)\u27. The structure was refined by least squares to R = 0.097 by using 1754 independent reflections collected to 28, = 65 and corrected for absorption. The P-N distance is 2.021 (5) A. In nitromethane solution, Raman, \u27H NMR, cryoscopic, and conductivity measurements are interpreted in terms of equilibria involving CIH4N2.PCIS, pyrazine, molecular PCI,, and ions originating from the ionization of PCls and C4H4N2.PClS

Crystal Structures, Phase Transitions and Energy Calculations of Poly(p-phenylene) Oligomers

The room temperature crystal structures, unit cell dimensions at 110K and phase transitions of three poly(p-phenylene) oligomers are reported. The structures of p-quinquephenyl (PQP), C30H22,p-sexiphenyl (PSP), C36H26, and p-septiphenyl (PSeptiP), C42H30, each belonging to space group P21/c, are similar to those of shorter oligomers. The unit cell dimensions are a = 22.056 Å, b = 5.581 Å, c = 8.070 Å and β = 97.91° for PQP, a = 26.241 Å, b = 5.568 Å, c = 8.091 Å and β = 98.17 ° for PSP, and a = 30.577 Å, b = 5.547 Å, c = 8.034 Å and β = 100.52 ° for PSeptiP. The a axis increases with molecular length. The molecules are linear and planar in all three structures. The herringbone nature of the packing is similar for PQP and PSeptiP, while a considerably greater tilt occurs in PSP. At 110K, the unit cell parameters b and c are approximately doubled while a remains nearly the same as in the room temperature cell. A time-dependent solid state transition is observed for PQP, PSP and PSeptiP when crystals are cooled to 110K. At elevated temperatures, thermal measurements indicate the oligomers to be thermotropic liquid crystals. The crystal-smectic transition temperatures are reported for PQP, PSP, PSeptiP and p-octiphenyl (POP), C48H34. The results of a molecular mechanics study on the conformation and packing of PSP are also presented. The competition between intramolecular forces (such as ortho hydrogen repulsions) and intermolecular crystal packing forces was examined in particular. Molecular mechanics calculations predict non-planar conformations in isolated polyphenyls, implying that conjugation between phenyl rings is insufficient to overcome ortho hydrogen repulsions. In a crystalline environment, however, intermolecular forces tend to force a planar conformation. Calculations on arrays of PSP molecules show that changing the phenyl-phenyl torsion angles from the coplanar value increases the total energy of the structure. The most favourable intermolecular interactions between oligomers are achieved for conformations having the phenyl rings coplanar

Crystal Structures, Phase Transitions and Energy Calculations of Poly(p-phenylene) Oligomers

The room temperature crystal structures, unit cell dimensions at 110K and phase transitions of three poly(p-phenylene) oligomers are reported. The structures of p-quinquephenyl (PQP), C30H22,p-sexiphenyl (PSP), C36H26, and p-septiphenyl (PSeptiP), C42H30, each belonging to space group P21/c, are similar to those of shorter oligomers. The unit cell dimensions are a = 22.056 Å, b = 5.581 Å, c = 8.070 Å and β = 97.91° for PQP, a = 26.241 Å, b = 5.568 Å, c = 8.091 Å and β = 98.17 ° for PSP, and a = 30.577 Å, b = 5.547 Å, c = 8.034 Å and β = 100.52 ° for PSeptiP. The a axis increases with molecular length. The molecules are linear and planar in all three structures. The herringbone nature of the packing is similar for PQP and PSeptiP, while a considerably greater tilt occurs in PSP. At 110K, the unit cell parameters b and c are approximately doubled while a remains nearly the same as in the room temperature cell. A time-dependent solid state transition is observed for PQP, PSP and PSeptiP when crystals are cooled to 110K. At elevated temperatures, thermal measurements indicate the oligomers to be thermotropic liquid crystals. The crystal-smectic transition temperatures are reported for PQP, PSP, PSeptiP and p-octiphenyl (POP), C48H34. The results of a molecular mechanics study on the conformation and packing of PSP are also presented. The competition between intramolecular forces (such as ortho hydrogen repulsions) and intermolecular crystal packing forces was examined in particular. Molecular mechanics calculations predict non-planar conformations in isolated polyphenyls, implying that conjugation between phenyl rings is insufficient to overcome ortho hydrogen repulsions. In a crystalline environment, however, intermolecular forces tend to force a planar conformation. Calculations on arrays of PSP molecules show that changing the phenyl-phenyl torsion angles from the coplanar value increases the total energy of the structure. The most favourable intermolecular interactions between oligomers are achieved for conformations having the phenyl rings coplanar

Nature of Phosphorus(V) Chloride in Ionizing and Nonionizing Solvents

Laser Raman spectra in conjunction with freezing point depression measurements provide evidence for two competing equilibria in the ionizing solvents CHICN, CH3N02, and C6H5N02, (1) 2PC15 8 PC14+ + PCl6- and (2) PCls s PC14+ + C1-, with (1) being predominant above about 0.03 m and (2) being predominant at lower concentrations. These observations resolve earlier conflicting reports on the ionization scheme in acetonitrile and nitrobenzene. The nature of phosphorus(V) chloride has also been studied in nonionizing solvents. When cryoscopic data are treated in the usual manner (neglect of possible solid solution formation) the apparent molecular weight in C6H6 supports the monomeric formulation PC15, while in CCl, the apparent molecular weight supports the dimeric formulation P2C110. This study has shown, however, that solid solution formation does occur in the carbon tetrachloride-phosphorus(V) chloride system and that it cannot be neglected. Application of the experimentally determined coefficient for the distribution of solute between solid and liquid phases (mole fraction of solute in solid phase :mole fraction of solute in liquid phase = 0.50 + 0.02 at infinite dilution) to correct for solid solution formation gives an apparent molecular weight which is in excellent agreement with monomeric PCls