SET‐LRP of acrylonitrile in ionic liquids without any ligand

Use of ionic liquids as reaction media was investigated in the design of an environmentally friendly single electron transfer‐living radical polymerization (SET‐LRP) for acrylonitrile (AN) without any ligand by using Fe(0) wire as catalyst and 2‐bromopropionitrile as initiator. 1‐Methylimidazolium acetate ([mim][AT]), 1‐methylimidazolium propionate ([mim][PT]), and 1‐methylimidazolium valerate ([mim][VT]) were applied in this study. First‐order kinetics of polymerization with respect to the monomer concentration, linear increase of the molecular weight, and narrow polydispersity with monomer conversion showed the controlled/living radical polymerization characters. The sequence of the apparent polymerization rate constant of SET‐LRP of AN was k_app ([mim][AT]) > k_app ([mim][PT]) > k_app ([mim][VT]). The living feature of the polymerization was also confirmed by chain extensions of polyacrylonitrile with methyl methacrylate. All three ionic liquids were recycled and reused and had no obvious effect on the controlled/living nature of SET‐LRP of AN. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Biodegradable aromatic copolyesters made from bicyclic acetalized galactaric acid

Random poly(hexamethylene terephthalate‐co‐galactarate)s and poly(dodecamethylene terephthalate‐co‐galactarate)s copolyesters covering the whole range of compositions were obtained with weight‐average molecular weights of ～30,000–50,000 g mol^?1 by melt polycondensation. They were thermally stable above 300 °C, and displayed T_g in the +20 to ?20 °C range with values steadily decreasing with the content in galactarate units. All the copolyesters were semicrystalline with T_m between 50 and 150 °C and those made from dodecanediol were able to crystallize from the melt at a crystallization rate depending on composition. Copolyesters containing up to 50% of galactaric units retained the crystal structure of their respective polyterephthalate homopolyesters, whereas they adopted the structure of the respective polygalactarates when the content in Galx units reached 70%. Stress‐strain essays revealed decay in the mechanical parameters as the aromatic units were replaced by Galx. Incubation in aqueous buffer revealed that hydrolysis of the polyesters were largely enhanced by copolymerization and evidenced the capacity of the Galx unit for making aromatic polyesters susceptible to biodegradation. A detailed NMR analysis complemented by SEM observations indicated that hydrolysis took place by preferred splitting of galactarate ester bonds with releasing of alkanediol and Galx‐diacid. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Validation of a novel very large eddy simulation method for simulation of turbulent separated flow

The paper describes the validation of a newly developed very LES (VLES) method for the simulation of turbulent separated flow. The new VLES method is a unified simulation approach that can change seamlessly from Reynolds‐averaged Navier–Stokes to DNS depending on the numerical resolution. Four complex test cases are selected to validate the performance of the new method, that is, the flow past a square cylinder at Re = 3000 confined in a channel (with a blockage ratio of 20%), the turbulent flow over a circular cylinder at Re = 3900 as well as Re = 140,000, and a turbulent backward‐facing step flow with a thick incoming boundary layer at Re = 40,000. The simulation results are compared with available experimental, LES, and detached eddy simulation‐type results. The new VLES model performs well overall, and the predictions are satisfactory compared with previous experimental and numerical results. It is observed that the new VLES method is quite efficient for the turbulent flow simulations; that is, good predictions can be obtained using a quite coarse mesh compared with the previous LES method. Discussions of the implementation of the present VLES modeling are also conducted on the basis of the simulations of turbulent channel flow up to high Reynolds number of Re_τ = 4000. The efficiency of the present VLES modeling is also observed in the channel flow simulation. From a practical point of view, this new method has considerable potential for more complex turbulent flow simulations at relative high Reynolds numbers. Copyright © 2013 John Wiley & Sons, Ltd.     

A Facile Preparation of N2-Arylisocytosines

N²-Arylisocytosines were obtained in good yields varying from 59 to 96% by a simple two-step process starting from 2-thiouracil via readily accessible 2-(methylthio)pyrimidin-4(3H)-one.     

Density Functional Theory Study of Hypoxanthine Tautomerism in Both the Isolated State and a Modeled-Ideal Aqueous Solution at Several Heterocyclic Protonation Levels

In order to advance the knowledge of prototropic tautomerism from the physicochemical point of view, the purine derivative hypoxanthine has been selected and studied. The overall purpose has been to explore thermodynamic aspects of the heterocycle tautomerism under the influence of both its protonation level and the surrounding dielectric constant. A Density Functional Theory study (at the B3LYP/6-31++G** level) was performed, in which the energetic and thermodynamic stabilities, the electric dipole moment values, the tautomeric equilibrium constants and the tautomeric populations were obtained for several hypoxanthine tautomers under systematically modified heterocyclic protonation levels, considering both isolated and ideal aqueous solution states. Among the interesting results obtained are changes in the tautomeric populations for several heterocyclic protonation states and with the increase of the dielectric constant. Several of the predictions made for an aqueous solution show good agreement with recently reported experimental conclusions. Also, the ionizable groups that contribute to the different hypoxanthine ionization steps in the main tautomers have been established. These and other related results are presented and discussed. Finally, the confidence developed in the predicted tautomeric populations in a modeled-ideal aqueous solution allows us to propose that the methodology applied here can be used for the study of prototropic tautomerism in heterocycles belonging to this class, particularly when the experimental work is challenging in both performance and physicochemical data analysis.     

13C NMR quantification of mono and diacylglycerols obtained through the solvent‐free lipase‐catalyzed esterification of saturated fatty acids

In the present investigation, we studied the enzymatic synthesis of monoacylglycerols (MAG) and diacylglycerols (DAG) via the esterification of saturated fatty acids (stearic, palmitic and an industrial residue containing 87% palmitic acid) and glycerol in a solvent‐free system. Three immobilized lipases (Lipozyme RM IM, Lipozyme TL IM and Novozym 435) and different reaction conditions were evaluated. Under the optimal reaction conditions, esterifications catalyzed by Lipozyme RM IM resulted in a mixture of MAG and DAG at high conversion rates for all of the substrates. In addition, except for the reaction of industrial residue at atmospheric pressure, all of these products met the World Health Organization and European Union directives for acylglycerol mixtures for use in food applications. The products were quantified by ¹³C NMR, with the aid of an external reference signal which was generated from a sealed coaxial tube filled with acetonitrile‐d3. After calibrating the area of this signal using the classical external reference method, the same coaxial tube was used repeatedly to quantify the reaction products. Copyright © 2012 John Wiley & Sons, Ltd.     

Multinuclear magnetic resonance studies of 2‐aryl‐1,3,4‐selenadiazoles

2‐Aryl‐1,3,4‐selenadiazoles were studied by ¹H, ¹³C, ¹⁵N and ⁷⁷Se NMR spectroscopy. The results (chemical shifts and coupling constants) were correlated with Hammett substituent parameters as well as calculated chemical shifts and bond lengths. Copyright © 2012 John Wiley & Sons, Ltd.     

Expanding the Scope of Arylsulfonylacetylenes as Alkynylating Reagents and Mechanistic Insights in the Formation of Csp2?Csp and Csp3?Csp Bonds from Organolithiums

We describe the unexpected behavior of the arylsulfonylacetylenes, which suffer an “anti‐Michael” addition of organolithiums producing their alkynylation under very mild conditions. The broad scope, excellent yields, and simplicity of the experimental procedure are the main features of this methodology. A rational explanation of all these results can be achieved by theoretical calculations, which suggest that the association of the organolithiums to the electrophile is a previous step of their intramolecular attack and is responsible for the unexpected “anti‐Michael” reactions observed for substituted sulfonylacetylenes.