Dichloropentafluoropropanes as solvents for size exclusion chromatography

We have found that HCFC225s (HCFC225ca: 3,3-dichloro-1,1,1,2,2-pentafluoropropane, HCFC225cb: 1,3-dichloro-1,1,2,2,3-pentafluoropropane) are superior mobile phases for size exclusion chromatography (SEC). As alternatives of CFC113, they have been shown to possess a number of excellent properties, such as low flammability, low viscosity, low cost, high purity, and environmental and operational friendliness. In addition, they have distinct advantages for the SEC measurement, because they solubilize some kinds of acrylate such as poly(methyl methacrylate) (PMMA) and commercial monodispersed PMMA can be used to prepare calibration curves necessary for the measurement of equivalent molecular weight of some polymers. Furthermore, we propose an HCFC225/1,1,1,3,3,3-hexafluoroisopropanol mixed solvent for use in the SEC of poly(ethylene terephthalate) (PET) and polyamides. Poly(2-(perfluorooctyl)ethyl acrylate), whose PMMA equivalent weight average molecular weight was 118,100 Da, was evaluated by a multi-angle laser light scattering (MALLS) detector to have an absolute molecular weight of 439,000 Da. The difference can be attributed to the molecular size of the polyfluorinated polymer compared to the non-fluorinated one. The possible application of this novel mobile phase system for molecular size and molecular weight characterization of perfluoropolyethers, PET, nylon 6 and nylon 6,6 are also discussed.     

An entirely new methodology for synthesizing perfluorinated compounds: synthesis of perfluoroalkanesulfonyl fluorides from non-fluorinated compounds

A new synthetic procedure for the preparation of perfluoroalkanesulfonyl fluorides utilizing liquid-phase direct fluorination with elemental fluorine has been developed. Direct fluorination of a partially fluorinated ester, which has alkanesulfonyl fluoride in the end, was synthesized from non-fluorinated counterparts and perfluorinated acid fluoride according to the PERFECT process, gave the desired perfluorinated product in moderate yield as well as by-products arising from CS bond cleavage. The results of the direct fluorination of some model substrates suggest that the CS bond cleavage occurred due to radical formation at the α-position rather than the β-position.     

2-hydroxymethyl-4-phenylthio-1-butene as a key compound for total synthesis of acyclic terpenoids

A new total synthesis of myrcene, citral, squalane, and isophytol employing 2-hydroxymethyl-4-phenylthio-1-butene as a starting material is described.     

Energetics and volume changes in electron attachment to pyrazine in supercritical xenon

The attachment of electrons to pyrazine occurs reversibly over a wide range of pressures at and above room temperature in supercritical xenon. The rate constant for attachment increases with pressure at low pressures, passes through a maximum, and levels off at values of 1-3x10(12) m(-1) s(-1) at high pressure. The activation volumes for attachment (DeltaVa*) are quite small but show maxima near the compressibility maxima. In contrast, DeltaVa* is always negative for this reaction in sc-ethane and exhibits minima near the compressibility maxima. The rate constants for electron detachment change little with pressure but increase with temperature. Activation volumes for detachment are small. To explain the small volume change observed for this reaction, it is proposed that at the higher pressures clustering around the neutral pyrazine is comparable to that around the ion; i.e., the partial molar volumes are comparable. The free energy change (DeltaGr) of this reaction decreases between 40 and 60 bar and then is fairly constant at higher pressures. The dependence of DeltaGr on pressure is consistent with clustering around the neutral pyrazine at higher pressure. Also, the electron affinity of the clusters, pyrazineXen, increases with n to a few tenths of an eV.     

Catalytic cyclization of o-alkynylbenzaldehyde acetals and thioacetals. Unprecedented activation of the platinum catalyst by olefins. Scope and mechanism of the reaction

A general protocol for the synthesis of functionalized indenes from o-alkynylbenzaldehyde acetals and thioacetals has been elaborated. Acetals uniformly give cyclization products having the alkyl group from the starting acetylene migrated to the alpha-position, whereas the cyclization of the corresponding thioacetals proceeds without alkyl migration. Optimization of the catalytic system for the cyclization of o-alkynylbenzaldehyde acetals revealed an unknown activation effect: PtCl(2) was found to be a better catalyst for the cyclization of acetals in the presence of olefins than without. A similar catalytic system (PtCl(2)/benzoquinone) has been found to be appropriate for the cyclization of cyclic acetals, whereas the optimal catalyst for the reaction of thioacetals is PdI(2). NMR monitoring of two reactions, acetal 3a + Pd(CH(3)CN)Cl(2) in CD(3)CN and thioacetal 5j + PdI(2) in CD(2)Cl(2), revealed that in both reactions similar cationic species are formed at the early stage of the transformation. Computational data (B3LYP/SDD level of theory) suggest that the difference in the reaction pathways for acetals and thioacetals can be rationalized by taking into account the relative stabilities of the corresponding vinylpalladium intermediates (22 vs 20 and 19 vs 21), which suggests a reversible thermodynamically controlled alkyl migration in the intermediate vinylcationic species.     

First functionalized MRI contrast agent recognizing vascular lesions.

A new MRI-contrast agent, EB-DTPA-Gd, that has an Evans Blue analogue as a sensing unit for endothelium lesions, was designed and synthesized. The agent also has diethylenetriamine-N,N,N',N",N"-pentaacetic acid-Gd complex (Gadolinium-DTPA) units, which have been used as detection units for T1-weighted MRI. The EB-DTPA-Gd was able to recognize and adsorb to the vascular endothelium-denuded region of porcine aorta, and to decrease the relaxation time of circumferential water's protons, making possible MR imaging of the endothelium-denuded region. The compound can be employed as a contrast agent for the imaging of vascular lesions using MRI.     

Ion‐Pair‐Based Assemblies Comprising Pyrrole–Pyrazole Hybrids

Modified 3,5‐dipyrrolylpyrazole (DPP) derivatives in their protonated form produce planar [2+2]‐type complexes with trifluoroacetate (TFA) ions. These complexes serve as constituent components of ion‐pair‐based assemblies. An essential strategy for the construction of dimension‐controlled organized structures based on these [2+2]‐type complexes is the introduction of aryl rings bearing long alkyl chains, which enables the formation of 2D patterns at interfaces, supramolecular gels, and mesophases.