Reaction of carbonyl fluoride with fluorine in the presence of various fluorides as catalysts

The fluorides KF, RbF and CsF have been known to serve as catalysts for the reaction CF₂O + F₂→ CF₃OF. The list of catalysts for this process has now been enlarged to include NaF, MgF₂, CaF₂, SrF₂, BaF₂ and LaF₃. Lithium fluoride and thorium fluoride also give CF₃OF but are less active. Perhaps the substances CsF·HF, KAgF₄ and NiF₂ should be included in this list. Silver fluoride, usually as a mixture of AgF₂ with AgF, has been known to catalyze the reaction of CF₂O with F₂ to give both CF₃OF and CF₃OOCF₃. The proportion of the latter in the mixture of products increases with decreasing temperature. At 25°, the reaction is slow and the yield of CF₃OOCF₃ is very high. It has now been shown that TIF₃ behaves like silver fluoride. It has also been shown that many other fluorides of metals give higher yields of CF₃OOCF₃ than of CF₃OF but require higher temperatures than AgF₂ (100-ca. 150°) to be effective. Various possible mechanisms for these catalytic processes are discussed.     

Stereoselective enolizations mediated by magnesium and calcium bisamides: contrasting aggregation behavior in solution and in the solid state

The reactions of magnesium and calcium bis(hexamethyldisilazide) with propiophenone have been studied with a view to determine the utility of these bases in the stereoselective enolization of ketones and to uncover the nature of the metal enolate intermediates produced. Both base systems are highly Z-selective when the reactions are conducted in the presence of polar solvents. However, in situ monitoring of the magnesium system in arene solution revealed a preference for E-enolate formation, which was confirmed by silyl enol ether trapping studies. Solution NMR studies of the magnesium system in toluene-d8 show the presence of a monomer-dimer equilibrium for the intermediate amidomagnesium enolates. This assignment is supported by the characterization of a disolvated amidomagnesium enolate dimer by crystallographic analysis. Comparative studies of the calcium system show distinctly different behavior. This is exemplified by the characterization of a novel solvent-separated ion pair complex and a monomeric amidocalcium enolate in the solid state. Solution NMR studies of the calcium system in pyridine-d5 reveal the co-existence of the heteroleptic amidocalcium enolate, the bisamide, the bisenolate and the ion pair complex.     

CLEARANCE TIMES OF PORPHYRIN DERIVATIVES FROM MICE AS MEASURED BY in vivo FLUORESCENCE SPECTROSCOPY

The clearance times of 17 different porphyrin derivatives from SKH:HR-1 mice have been measured using the technique of in vivo fluorescence spectroscopy. This technique monitors the in vivo porphyrin fluorescence observed from the external skin surface. Most hydrophilic porphyrin derivatives show relatively short clearance times, in the order of 2.5-6 h. The dicarboxylic acid porphyrins, proto-, hydroxyethylvinyldeutero- and hematoporphyrin IX have clearance times of 7.8, 12.2 and 14.7 h respectively. The mixture hematoporphyrin derivative has an intermediate clearance time of 12.6 h. N-methylated porphyrins show clearance times in the vicinity of 15-22 h. Monoaspartyl chlorin e6 shows the longest clearance time of all porphyrin derivatives measured (30.3 h).     

Vinylation and polymerization with trivinylaluminum. I. Vinylation of organic halides as a model for termination in cationic polymerization leading to vinyl end groups

An improved synthesis of trivinylaluminum (V₃Al) is described. The proton magnetic resonance (PMR) spectrum of V₃Al was recorded and analyzed. A new vinylation method involving the use of V₃Al as the vinylating agent has been developed, and the vinylation of organic halides by V₃Al was studied at ?30, ?50 and ?70°C. Primary alkyl chlorides, such as methyl and methylene chloride, do not react with V₃Al and were used as solvents. Secondary chlorides such as 2-chloropropane also do not react. t-Butyl chloride gives rise to t-butylethylene (70–98%), depending on reaction conditions, and the allylic chlorides, 3-chloro-1-butene, and 3-chloro-3-methyl-1-butene, yield the expected vinylated products and their isomers (～90%). Allyl and benzyl chloride do not react under the conditions tried. The reaction between V₃Al and the ditertiary dichloride 2,6-dichloro-2,6-dimethylheptane yields several isomeric C₁₃H₂₄ and C₁₁H₂₀ hydrocarbons; however, surprisingly, C₉H₁₆ does not form. The C₁₃ hydrocarbons arise by divinylation at the termini of the dichloride, while the C₁₁ hydrocarbons are formed by vinylation at one and proton elimination at the other terminus of the dichloride. The presence of unsaturated C₁₃H₂₄ and C₁₁H₂₀ isomers is most likely due to proton induced isomerization. These results are explained by a proximity effect involving vinylation at one end of the dichloride by V₃Al followed by rapid reaction of the second chlorine (mostly) by V₂AlCl generated in situ during the first vinylation in the proximity of the chloride. At the other chlorine terminus V₂AlCl causes either a second vinylation (leading to C₁₃ hydrocarbons) or a proton elimination (leading to C₁₁ hydrocarbons). The absence of C₉H₁₆ among the reaction products indicates that V₃Al exclusively effects vinylation. The RCl + V₃Al ← RV + V₂AlCl reaction may be regarded as a model for initiation followed by immediate termination in cationic olefin polymerization, a process leading to vinyl-ended polymers.     

Determination of phosphorus in polymers by INAA

An INAA technique employing beta spectrometry was developed for the determination of phosphorus in polymers. The (n,γ) reaction on phosphorus produces³²P, half-life 14.3 days, a pure beta emitter with end-point energy 1.71 MeV. Polymer samples in the form of powders, films and pellets are irradiated and then counted with a plastic scintillator. The beta spectrum is corrected for interferences (especially Sb, Zn and Br which are quantified by gamma spectrometry) and for energy loss in the thick sample. Samples must also be analyzed for S and Cl which cause nuclear interferences. With an irradiation time of 4 hours at a neutron flux of 5·10¹¹ n·cm^{−2 s −1}, decay time 10 days and counting time 10 minutes, the sensitivity is 520 counts/μg phosphorus and the detection limit is typically 2μg/g.     

Polymerizability,copolymerizability, and properties of cyanoacrylate‐telechelic polyisobutylenes I: three‐arm star cyanoacrylate‐telechelic polyisobutylene

This series of papers concern new materials for possible biological applications created by combining the chemistry of highly reactive cyanoacrylates (CAs) with polyisobutylene (PIB) rubbers. First, a new strategy for the synthesis of CA–telechelic PIBs is described. Subsequently, the strategy is employed for the synthesis of low viscosity (syringible) CA–telechelic three‐arm star PIB [Ø(PIB–CA)₃]. The intermediates of the synthesis route are characterized by ¹H NMR spectroscopy. Injecting liquid Ø(PIB–CA)₃ into living tissue (fresh chicken egg) produces a bolus of crosslinked PIB rubber. The spectacular oxidative resistance of this rubber is documented by its resistance to concentrated HNO₃. A structural model of the crosslinked rubber obtained upon contacting Ø(PIB–CA)₃ with proteinaceous tissue is proposed. Copyright © 2007 John Wiley & Sons, Ltd.     

Synthesis and characterization of novel poly(vinyl chloride)‐based grafts: Poly(vinyl chloride‐co‐2‐chloropropene) fitted with multiple high‐glass‐transition‐temperature polyolefin branches

The tertiary chlorine (Cl^t) content of vinyl chloride/2‐chloropropene copolymers [P(VC‐co‐2CP)] was determined by NMR spectroscopy. Copolymers containing 6.8–47.0 Cl^t's per P(VC‐co‐2CP) chain were used to initiate the cationic grafting of α‐methylstyrene, norbornadiene, indene, and norbornene with Et₂AlCl under various conditions. Grafting was demonstrated by selective solvent extraction, and the effect of the experimental conditions on the grafting efficiency was examined. Select rheological and thermal characteristics of P(VC‐co‐2CP) grafts, including the glass‐transition temperature, heat deflection temperature, and discoloration upon heating, were studied. P(VC‐co‐2CP) carrying 7–11 poly(α‐methylstyrene) or polynorbornadiene branches per chain raised the glass‐transition temperature to, or above, that of a blend control. P(VC‐co‐2CP)s fitted with polyindene or polynorbornene branches were less effective in raising the mechanical properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3644–3651, 2002