Palladium catalyzed Suzuki C-C couplings in an ionic liquid: nanoparticles responsible for the catalytic activity

A new family of functionalized ligands derived from norborn-5-ene-2,3-dicarboxylic anhydride has been used in Suzuki C-C cross-couplings between aryl boronic acids and aryl bromide derivatives in [BMI][PF(6)] (BMI=1-n-butyl-3-methyl-imidazolium), using palladium acetate as catalytic precursor. High conversions and yields are obtained when amine ligands containing hydroxy groups are involved. TEM analyses after catalysis show the formation of small nanoparticles, in contrast to the agglomerates observed when nanoparticles are intentionally preformed, with a consequent decrease in the catalytic activity in the latter case. Some tests, including the correlation effect between solvent and ligand, are carried out to try to identify the true nature of the catalyst. All the results obtained suggest that formation of nanoparticles is required to lead to a catalytically active system.     

Deconvolution of Molecular Weight Distributions Using Dynamic Flory‐Schulz Distributions

Summary: The deconvolution of molecular weight distributions (MWDs) may be useful for obtaining information about the polymerization kinetics and properties of catalytic systems. However, deconvolution techniques are normally based on steady‐state assumptions and very little has been reported about the use of non‐stationary approaches for the deconvolution of MWDs. In spite of this, polymerization reactions are often performed in batch or semi‐batch modes. For this reason, dynamic solutions are proposed here for simple kinetic models and are then used for deconvolution of actual MWD data. Deconvolution results obtained with dynamic models are compared to deconvolution results obtained with the standard stationary Flory‐Schulz distributions. For coordination polymerizations, results show that dynamic MWD models are able to describe experimental data with fewer catalytic sites, which indicates that the proper interpretation of the reaction dynamics may be of fundamental importance for kinetic characterization. On the other hand, reaction dynamics induced by modification of chain transfer agent concentration seem to play a minor role in the shape of the MWD in free‐radical polymerizations.

This Figure illustrates that MWDs obtained at unsteady conditions should not be deconvoluted with standard steady‐state Flory‐Schulz distributions.     

Isothermal curing of an epoxy resin by alternating differential scanning calorimetry

The quasi-isothermal curing of a diepoxide resin with a triamine of polyoxypropylene was studied by alternating differential scanning calorimetry (ADSC), which is a temperature modulated DSC technique. The complex heat capacity measurements allows to analyse the vitrification process at curing temperatures (T_c) below the maximum glass transition of the fully cured epoxy (T_g∞=85.8°C). Initially, the modulus of the complex heat capacity, |C^*_p|, increases until a maximum (conversion between 0.42 and 0.56) and then decreases. This step is followed by an abrupt decay of |C^*_p|, due to the vitrification of the system, which allows the determination of the vitrification time. This value agrees well with that determined by the partial curing method. The phase angle and out-of-phase heat capacity show an asymmetric wide peak during the vitrification process. The change in |C^*_p| at vitrification decreases with the increase of T_c becoming zero at temperature T_g∞. This epoxy-triamine system shows a delay of the vitrification process respect to other model epoxy systems probably due to the presence of polyoxypropylene chains in the network.

The decay of |C^*_p| during vitrification may be normalised between unity and zero by defining a mobility factor. This mobility factor has been used to simulate the reaction rate during the stage where the reaction is controlled by diffusion. The observed reaction rate is simulated by the product of the kinetic reaction rate, determined by the autocatalytic model, and the mobility factor.     

Analysis of organic compounds of water-in-crude oil emulsions separated by microwave heating using comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry

In this work the higher peak capacity and resolution of comprehensive two-dimensional gas chromatography (GCxGC) has been successfully applied, for the first time, to tentatively identify several polar organic compounds of organic extracts of aqueous phases resulting from microwave demulsification process of water-in-crude oil emulsions. Results have shown that higher temperatures and longer exposure time to microwave irradiation produced water phases with a wider variety of polar organic compounds. The microwave process showed to be suitable for the extraction of several polar compounds classes of petroleum. The proposed microwave extraction method and GCxGC identification of polar compounds of petroleum samples are of practical interest for the petrochemical industry due to corrosion and related problems associated with these polar compounds in refinery equipments. The GCxGC/time-of-flight MS technique shows to be very important in the total separation of different classes of compounds and allows the identification of many compounds in these classes.     

Microwave Effects Due to Anionic or Cationic Initiators in Emulsion Polymerization Reactions

Summary: Emulsion polymerization reactions were performed under microwave irradiation and conventional heating using anionic or cationic initiators and surfactants. Microwave irradiation promoted higher reaction rates for both initiators and surfactants, in comparison with the conventional heating. The effect of high power microwave irradiation was studied using a method of cycles of heating and cooling, where rapid polymerization reactions were obtained. In the reactions with anionic initiator and surfactant, a decrease in the particle diameters was observed with microwave heating, and even smaller particles were obtained using high power microwave irradiation. Moreover, the decrease in the particle size was acompanied by an increase in the polymer molecular weight. On the other hand, these effects were not observed for reactions with cationic initiator and surfactant.     

C-H bond activation and subsequent C-C bond formation promoted by osmium: 2-vinylpyridine-acetylene couplings

Complex OsH2Cl2(PiPr3)2 promotes the C-H activation of 2-vinylpyridine and subsequently couples the activated substrate with a second 2-vinylpyridine and two acetylene molecules. In the absence of 2-vinylpyridine, the activated substrate is coupled with an acetylene unit to afford a 2-butadienylpyridine derivative.     

Probing particle size distributions in natural surface waters from 15 nm to 2 microm by a combination of LIBD and single-particle counting

We present a technique for measuring colloid size distributions between 15 nm and 2 microm at concentrations relevant to natural surface waters. Two particle-measuring methods are combined: laser-induced breakdown detection (LIBD), which allows the quantification of colloid size distributions below 400 nm, and a commercial single-particle counter that extends the accessible size range up to two mum. Centrifugation was used in order to separate micrometer sized particles for the LIBD measurement. The feasibility is demonstrated on water of Lake Brienz (Switzerland) and the River Pfinz (Germany) and the particle size distributions follow Pareto's law even down to 15 nm in both cases.     

Can the disproportion of oxidation state III be favored in RuII-OH2/RuIV=O systems?

Three new Ru-aqua complexes containing a mixed carbene and pyridylic ligands with general formulas [Ru(CNC)(bpy)(H2O)](PF6)2 (1) (CNC is 2,6-bis(butylimidazol-2-ylidene)pyridine; bpy is 2,2'-bipyridine) and cis-/trans-[Ru(CNC)(nBu-CN)(H2O)](PF6)2 (cis-2 and trans-2) (nBu-CN is 2-(butylimidazol-2-ylidene)pyridine) have been prepared and structurally characterized both in the solid state (monocrystal X-ray diffraction analysis for 1 and for the related complex trans-[Ru(Br)(CNC)(nBu-CN)](PF6)) and in solution (for all of them) through NMR. The electrochemical properties of these three Ru-aqua complexes have been investigated by cyclic voltammetry, differential pulse voltammetry and Coulombimetric techniques. It is found that, for complex 1 at pH 7, the difference between the IV/III and the III/II redox couples (DeltaE1/2) is 50 mV, which is the smallest ever reported for this type of complex. On the other hand, for complexes cis-2 and trans-2, the oxidation state III is unstable with respect to disproportionation to II and IV. The reactivity of their Ru=O species has been tested toward cis-beta-methylstyrene oxidation, and it has been compared to [Ru(O)(trpy)(bpy)]2+. An inverse correlation between the degree of cis/trans-epoxide isomerization and DeltaE1/2 is found. In particular, for complexes cis-2 and trans-2, which have a DeltaE1/2 < 0, the epoxidation is highly stereoselective, yielding only cis-epoxide.