Atmospheric chemistry of CF3CF═CH2 and (Z)-CF3CF═CHF: Cl and NO3 rate coefficients, Cl reaction product yields, and thermochemical calculations

Rate coefficients, k, for the gas-phase reactions of Cl atoms and NO(3) radicals with 2,3,3,3-tetrafluoropropene, CF(3)CF═CH(2) (HFO-1234yf), and 1,2,3,3,3-pentafluoropropene, (Z)-CF(3)CF═CHF (HFO-1225ye), are reported. Cl-atom rate coefficients were measured in the fall-off region as a function of temperature (220-380 K) and pressure (50-630 Torr; N(2), O(2), and synthetic air) using a relative rate method. The measured rate coefficients are well represented by the fall-off parameters k(0)(T) = 6.5 × 10(-28) (T/300)(-6.9) cm(6) molecule(-2) s(-1) and k(∞)(T) = 7.7 × 10(-11) (T/300)(-0.65) cm(3) molecule(-1) s(-1) for CF(3)CF═CH(2) and k(0)(T) = 3 × 10(-27) (T/300)(-6.5) cm(6) molecule(-2) s(-1) and k(∞)(T) = 4.15 × 10(-11) (T/300)(-0.5) cm(3) molecule(-1) s(-1) for (Z)-CF(3)C═CHF with F(c) = 0.6. Reaction product yields were measured in the presence of O(2) to be (98 ± 7)% for CF(3)C(O)F and (61 ± 4)% for HC(O)Cl in the CF(3)CF═CH(2) reaction and (108 ± 8)% for CF(3)C(O)F and (112 ± 8)% for HC(O)F in the (Z)-CF(3)CF═CHF reaction, where the quoted uncertainties are 2σ (95% confidence level) and include estimated systematic errors. NO(3) reaction rate coefficients were determined using absolute and relative rate methods. Absolute measurements yielded upper limits for both reactions between 233 and 353 K, while the relative rate measurements yielded k(3)(295 K) = (2.6 ± 0.25) × 10(-17) cm(3) molecule(-1) s(-1) and k(4)(295 K) = (4.2 ± 0.5) × 10(-18) cm(3) molecule(-1) s(-1) for CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF, respectively. The Cl-atom reaction with CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF leads to decreases in their atmospheric lifetimes and global warming potentials and formation of a chlorine-containing product, HC(O)Cl, for CF(3)CF═CH(2). The NO(3) reaction has been shown to have a negligible impact on the atmospheric lifetimes of CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF. The energetics for the reaction of Cl, NO(3), and OH with CF(3)CF═CH(2) and (Z)-CF(3)CF═CHF in the presence of O(2) were investigated using density functional theory (DFT).     

Theoretical study on the hydrolysis mechanism of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine

The hydrolysis mechanisms of N,N-dimethyl-N′-(2′,3′-dideoxy-3′-thiacytidine)formamidine (FA-3TC) in the gas phase and in aqueous solution were studied by use of the density functional theory B3LYP/6-31 G(d, p) method. Two possible reaction pathways in the title reaction were considered. In one pathway water attacks the C=N double bond first (path A) while in the other water attacks the C—N single bond first (path B). The calculated results indicate that the first step in both pathways is the rate-limiting process and path A is more favorable than path B in the gas phase. The effect of solvent water on the title reaction was assessed at the B3LYP/6-31 G(d, p) level of theory based on the po-larizable continuum model (CPCM). In water the first mechanism (path A) is also favored.     

Reversible chain reaction between <Emphasis Type="Italic">N,N</Emphasis>′-diphenyl-1,4-benzoquinonediimine and 2,5-dichlorohydroquinone: Kinetics,mechanism, and the rate constants of elementary steps

The kinetics of the reversible chain reaction between N,N′-diphenyl-1,4-benzoquinonediimine and 2,5-dichlorohydroquinone was studied in chlorobenzene at 298 and 343 K. Experiments in the presence of an initiator proved that the reaction proceeds via a chain mechanism with a chain length of ～10⁴ to 10⁵ units, depending on the reactant and initiator concentrations and temperature. The reaction rate first increases and then decreases with increasing concentrations of the reaction products (N,N′-diphenyl-1,4-phenylenediamine and 2,5-dichloroquinone) due to the pronounced reversibility of the chain termination and propagation steps involving the reaction products. The reaction orders with respect to the components were determined. The rate constants and activation energies of most of the elementary steps of the forward and backward chain reactions were determined or reliably estimated. Induction periods were observed for the first time in the reversible chain reactions in the quinoneimine + hydroquinone systems. The induction periods are due to the long time required for the establishment of the steady-state radical concentrations in the system.     

What determines the rate of excited-state intramolecular electron-transfer reaction of 4-(N,N'-dimethylamino)benzonitrile in room temperature ionic liquids? A study in [bmim][PF6

The kinetics of excited-state intramolecular electron-transfer reaction and dynamics of solvation of the intramolecular charge transfer (ICT) state of 4-(N,N'-dimethylamino)benzonitrile (DMABN) was studied in 1-butyl-3-methylimidazloium hexafluorophosphate, [bmim][PF(6)], by monitoring the dual fluorescence of the system. The picosecond time-resolved emission spectra (TRES) of DMABN exhibit decay of the locally excited (LE) emission intensity and shift of the ICT emission peak position with time, thus capturing the kinetics of evolution of the ICT state from the LE state and solvent relaxation of the ICT state. These results show that the LE→ICT transformation rate is determined not by the slow dynamics of solvation in ionic liquid, but is controlled mainly by the rate of structural reorganization of the molecule, which accompanies the electron-transfer process in this polar viscous medium. Even though both solvent reorganization around photo-excited DMABN and structural rearrangement of the molecule are dependent on the viscosity of the medium, it is the latter process that contributes to the viscosity dependence of the LE→ICT transformation.     

An unexpected high erythro-selection in the Grignard reaction with an N,O-acetal: a concise asymmetric synthesis of indolizidine alkaloid (−)-2-epi-lentiginosine

Starting from commercially available lactone 10, a concise and highly diastereoselective synthesis of (?)-(lS,2R,8aS)-2-epi-lentiginosine (2) is described. The synthesis featured an unexpected highly erythro-selective reaction of Grignard reagent 7 with the protected N,O-acetal 8. The stereochemical outcome of this reaction is contrary to the known results involving the reactions with O-benzyl protected aminofuranosides and aminoglycosides. Thus, this method constitutes an extension of the threo-diastereoselective C–C bond formation methodology.     

Specific features of the reaction between tris(5-bromo-2-methoxyphenyl)antimony and 2-oxybenzaldoxime: Structure of bis(μ3-2-oxybenzaldoximato-O,O′,N)-(μ2-oxo)-bis(5-bromo-2-methoxyphenyl)antimony

Bis(μ₃-2-oxybenzaldoximato-O,O′,N)-(μ₂-oxo)-bis(5-bromo-2-methoxyphenyl)antimony, which crystallizes from toluene in the form of a solvate, has been synthesized by the reaction between tris(5-bromo-2-methoxyphenyl)antimony and 2-oxybenzaldoxime in the presence of hydrogen peroxide. According to X-ray diffraction data, the structurally equivalent antimony atoms in a binuclear complex molecule are linked via two tridentate bridging ligands and an oxygen atom and have a distorted octahedral coordination to the C₂O₃N surrounding The trans-angles of the octahedron are CSbO (168.7(1)°), CSbN (164.1(1)°), and OSbO (159.3(1)°), and the bond lengths are Sb-C (2.127(4), 2.159(3) Å) and Sb-N (2.238(3) Å). A molecule contains the three types of Sb-O distances with a bridging oxygen atom (1.950(1) Å), the oxygen atoms of oxy groups (2.002(2) Å), and the oxygen atoms of oxime groups (2.091(2) Å). Sb?OCH₃ intramolecular contacts (3.097, 3.290 Å) also exist.     

The Mannich reaction in the synthesis of N,S-containing heterocycles 11. Synthesis of 3,3′-(1,4-phenylene)-bis(8-aryl-6-oxo-3,4,7,8-tetrahydro-2H,6H-pyrido[2,1-b][1,3,5]thiadiazine-9-carbonitriles)

N-Methylmorpholinium 4-aryl-3-cyano-6-oxo-1,4,5,6-tetrahydropyridine-2-thiolates readily undergo the Mannich reaction with p-phenylenediamines and excess formaldehyde in the absence of a catalyst to form 3,3??-(1,4-phenylene)-bis(8-aryl-6-oxo-3,4,7,8-tetrahydro-2H,6H-pyrido[2,1-b][1,3,5]thiadiazine-9-carbonitriles) in moderate yields (24?C56%).     

Me2ESiMe3 (E = As,N, P) Compounds—Efficient Reagents for Replacement of the Fluorine Atom by Me2E Group in the Complex [(η6-1-F-3,5-Me2C6H3)(η5-C5EtMe4)Rh](CF3SO3)2 >

Russian Journal of Organic Chemistry -     

Comparative study of [RuClCp(HdmoPTA-κP)(PPh3)][CF3SO3] and the heterobimetallic complexes [RuClCp(PPh3)-μ-dmoPTA-1κP:2κ2N,N'-M(acac-κ2O,O')2] (M=Co, Ni, Zn; dmoPTA=3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane)

The synthesis of novel heterobimetallic derivatives of general formula [RuClCp(PPh(3))-μ-dmoPTA-1κP:2κ(2)N,N'-M(acac-κ(2)O,O')(2)] (M = Ni (3), Zn (4); dmoPTA = 3,7-dimethyl-1,3,7-triaza-5-phosphabicyclo[3.3.1]nonane) is described. The preparations of the ruthenium-cobalt analogue (M = Co (2)) and the starting compound [RuClCp(HdmoPTA-κP)(PPh(3))](CF(3)SO(3)) have been revised and their yield improved. Similar to 2, the solid state structures of 3 and 4 show that the dmoPTA-P and the dmoPTA-N(CH(3)) atoms are involved in the coordination to the {RuCpCl(PPh(3))} and {M(acac)(2)} moieties, respectively. The size of the diffusing units is almost the same for the three binuclear complexes, indicating that they exhibit similar solution structures. The diamagnetic ruthenium-zinc derivative was fully characterized in solution at 193 K by NMR as two diastereomeric pairs of enantiomers (R-Ru, Δ-Zn; R-Ru, Λ-Zn; S-Ru, Δ-Zn; S-Ru, Λ-Zn). Finally, the electrochemical properties of the complexes have been investigated by cyclic voltammetry.