Bis(perfluoroorganyl)bromonium salts [(RF)2Br]Y (RF = aryl, alkenyl, and alkynyl)

Bromonium salts [(R_F)₂Br]Y with perfluorinated groups R_FC₆F₅, CF₃CFCF, C₂F₅CFCF, and CF₃C≡C were isolated from reactions of BrF₃ with R_FBF₂ in weakly coordinating solvents (wcs) like CF₃CH₂CHF₂ (PFP) or CF₃CH₂CF₂CH₃ (PFB) in 30-90% yields. C₆F₅BF₂ formed independent of the stoichiometry only [(C₆F₅)₂Br][BF₄]. 1:2 reactions of BrF₃ and silanes C₆F₅SiY₃ (Y = F, Me) ended with different products - C₆F₅BrF₂ or [(C₆F₅)₂Br][SiF₅] - as pure individuals, depending on Y and on the reaction temperature (Y = F). With C₆F₅SiF₃ at ≥−30 °C [(C₆F₅)₂Br][SiF₅] resulted in 92% yield whereas the reaction with less Lewis acidic C₆F₅SiMe₃ only led to C₆F₅BrF₂ (58%). The interaction of K[C₆F₅BF₃] with BrF₃ or [BrF₂][SbF₆] in anhydrous HF gave [(C₆F₅)₂Br][SbF₆]. Attempts to obtain a bis(perfluoroalkyl)bromonium salt by reactions of C₆F₁₃BF₂ with BrF₃ or of K[C₆F₁₃BF₃] with [BrF₂][SbF₆] failed. The 3:2 reactions of BrF₃ with (C₆F₅)₃B in CH₂Cl₂ gave [(C₆F₅)₂Br][(C₆F₅)_nBF_4−n] salts (n = 0-3). The mixture of anions could be converted to pure [BF₄]⁻ salts by treatment with BF₃·base.     

Explored routes to unknown polyfluoroorganyliodine hexafluorides, RFIF6

Two routes to R_FIF₆ compounds were investigated: (a) the substitution of F by R_F in IF₇ and (b) the fluorine addition to iodine in R_FIF₄ precursors. For route (a) the reagents C₆F₅SiMe₃, C₆F₅SiF₃, [NMe₄][C₆F₅SiF₄], C₆F₅BF₂, and 1,4-C₆F₄(BF₂)₂ were tested. C₆F₅IF₄ and CF₃CH₂IF₄ were used in route (b) and treated with the fluoro-oxidizers IF₇, [O₂][SbF₆]/KF, and K₂[NiF₆]/KF. The observed sidestep reactions in case of routes (a) and (b) are discussed. Interaction of C₆F₅SiX₃ (X = Me, F), C₆F₅BF₂, 1,4-C₆F₄(BF₂)₂ with IF₇ gave exclusively the corresponding ring fluorination products, perfluorinated cyclohexadiene and cyclohexene derivatives, whereas [NMe₄][C₆F₅SiF₄] and IF₇ formed mixtures of C₆F_nIF₄ and C₆F_nH compounds (n = 7 and 9). CF₃CH₂IF₄ was not reactive towards the fluoro-oxidizer IF₇, whereas C₆F₅IF₄ formed C₆F_nIF₄ compounds (n = 7 and 9). C₆F₅IF₄ and CF₃CH₂IF₄ were inert towards [O₂][SbF₆] in anhydrous HF. CF₃CH₂IF₄ underwent C-H fluorination and C-I bond cleavage when treated with K₂[NiF₆]/KF in HF. The fluorine addition property of IF₇ was independently demonstrated in case of perfluorohexenes. C₄F₉CFCF₂ and IF₇ underwent oxidative fluorine addition at −30 °C, and the isomers (CF₃)₂CFCFCFCF₃ (cis and trans) formed very slowly perfluoroisohexanes even at 25 °C. The compatibility of IF₇ and selected organic solvents was investigated. The polyfluoroalkanes CF₃CH₂CHF₂ (PFP), CF₃CH₂CF₂CH₃ (PFB), and C₄F₉Br are inert towards iodine heptafluoride at 25 °C while CF₃CH₂Br was slowly converted to CF₃CH₂F. Especially PFP and PFB are new suitable organic solvents for IF₇.     

The palladium-catalysed cross-coupling reaction of lithium polyfluorophenyltrimethoxyborates with 4-fluoroiodobenzene

Li[C₆F₅B(OMe)₃], Li[C₆HF₄B(OMe)₃] (all three isomers) and Li[3,4,5-C₆H₂F₃B(OMe)₃] are the first examples of polyfluorophenyltrimethoxyborate salts which have been applied as reagents to Pd-catalysed cross-coupling reactions. A series of polyfluorinated biphenyls C₆H_5−nF_n-C₆H₄F-4′ were obtained from Li[C₆H_5−nF_nB(OMe)₃] and the model substrate 4-FC₆H₄I in the presence of Pd catalysts. The influence of the number and the position of fluorine atoms in the polyfluorophenyltrimethoxyborate salts on the reactivity in the coupling reaction was elucidated.     

Nonlinear Instability of the Two-Dimensional Striation Model About Smooth Steady States

The two-dimensional striation model consists of a nonlinear system of PDE's which arises in the modeling of the ionospheric plasma. The local-in-time existence of strong solutions is first proved using Banach's fixed point theorem. Then, under physically relevant assumptions, the system is shown to be nonlinearly unstable as soon as it is linearly unstable. Moreover, the instability occurs before the possible blow-up time of the solution. The proof relies on an earlier work of Hwang and Guo (2003 Hwang , H. J. , Guo , Y. ( 2003 ). On the dynamical Rayleigh–Taylor instability . Arch. of Rat. Mech. Anal. 167 : 235 – 253 .[Crossref], [Web of Science ®] , [Google Scholar]). The first step of the proof is to investigate under which conditions the linearized system is unstable and to prove that its spectrum is bounded, by means of a variational formulation. The second one consists in constructing a family of solutions depending on the parameter δ measuring the smallness of the perturbation to the steady-state. Thanks to the boundedness of the linearized spectrum, this family of solutions is shown to be unstable by means of a power series expansion in δ.     

Deformation of liquid droplets during collisions with hot walls: Experimental and Numerical Results

Measurements of droplet deformation during wall impingement were performed for ethanol droplets and water droplets with diameters ranging from 100 to 200 μm. The wall temperature is well above the Leidenfrost temperature of the droplet liquid. With monodisperse droplet streams and a special illumination technique, slow motion images of the phenomena can be obtained. Measurements with high temporal resolution below 1 μs are possible using a standard video camera. The experimental results are compared with numerical results, which were obtained by solving the three-dimensional Navier-Stokes equations for incompressible fluids including surface tension effects. The fluids are treated with the volume-of-fluid method and the free surface is modeled according to the continuum-surface-force model. Numerical and experimental results show good agreement.