Model Calculations and Experimental Studies as a Route Toward Simplification of the Kinetic Mechanism of the H2O2–NaSCN–NaOH–CuSO4 Homogeneous Oscillator

Oscillatory chemical reactions are usually characterized by complicated kinetic mechanisms in which the source of instability is combined with the parallel dissipative process. One of such systems is the H₂O₂–NaSCN–NaOH–CuSO₄ homogeneous oscillator, in which dynamic instabilities are associated with the irreversible oxidation of thiocyanate ions with hydrogen peroxide. Following our previous studies on this system, we now propose further intuitive and substantial simplification of its kinetic mechanism toward the scheme involving only five intermediates. Its compatibility with our previous, nine‐variable model is verified in terms of model calculations, compared with experimental potentiometric and spectrophotometric data. In particular, supercritical nature of a Hopf bifurcation as a route toward oscillations born out of a single steady state upon increasing catalyst (copper species) concentration was observed in the model and an analogous type of bifurcation is suggested by available experimental data. Our work is a step toward final reduction of the mechanism of the studied system to the “minimum oscillator,” the concept used earlier, e.g., for the Belousov–Zhabotinsky reaction, of however remarkably different kinetic mechanism.     

THE STEREOCHEMISTRY OF DEALKYLATION STEP IN THE ARBUZOV REACTION INVOLVING FIVE-COORDINATE INTERMEDIATE. EVIDENCE FOR EQUILIBRIUM BETWEEN PHOSPHORANE AND PHOSPHONIUM SPECIES

Abstract

The oxidative addition of molecules X–Y to three-coordinated phosphorus compounds is of considerable general interest. If one of the groups attached to the phosphorus atom is an alkoxy, OR, the final product is almost always > P(O)Y with the formation of an alkyl halide RX. The above process is known as Arbuzov reaction, the mechanism of which can be represented, in the light of our present knowledge, as follows: mental mechanistic problem for the Arbuzov reaction.

The R(?)phosphite (4) was prepared from R(+)2-octanol of 95% opt. purity, [α]²⁰ _D + 9.4° (neat) and the chlorophosphite (3) by standard condensation in the presence of tertiary amine and purified by distilla tion in vacuo, δ³¹P ?127.5 ppm, [α]^D ₂₀ ?25.6° (neat). Equimolar amounts of the phosphite (4) and the corresponding halogen in CH2 C12 solution were allowed     

Phosphonates Containing Sulfur and Silicon: New Stereochemical and Mechanistic Aspects

Abstract

Synthesis, reactivity and conformation of cyclic S,S-thioacetals of formylphosphonates are described. The chemistry of α-trimethylsilyl-α-methylthiometanephosphonate is briefly discussed.     

α-Phosphoryl Cyclopentanones as Possible Intermediates in the Total Synthesis of Sarkomycin

Abstract

In an effort to synthesize sarkomycin 1 trans-2-diphenylphosphinoyl-3-tris (methylthio) methyl-cyclopentanone 7 and trans-2-diphenylphosphinoyl-3-carbo-methoxy-cyclopentanone 8 were prepared. The Horner-Wittig reaction of the latter with formaldehyde failed. (±)-Sarkonycin 1 was prepared by a sequence of reactions starting from diethyl 2-oxopropanephosphonate. The key steps in this synthesis involve the intramolecular carbenoid cyclization of 1-diazo-2-oxopropanephosphonate 10 and the Horner-Wittig reaction of 2-diethoxyphosphoryl-3-carboxy-cyclopentanone 12 with formaldehyde.     

A New View of the Mechanistic Pathways in the Iodine Atom Transfer Addition Reaction Involving 1-Iodoalkylphosphonates and Related Nonphosphorus Systems

The title reaction in the initiation step proceeds via two mechanistic pathways involving attack of the isobutyronitrile radical either on the starting iodide or on the starting alkene or alkyne followed by the reaction of the adduct radical with the iodide.     

SYNTHESIS AND TRANSFORMATIONS OF OPTICALLY ACTIVE α-PHOSPHORYL SULPHOXIDES

Abstract

As part of a continuing studies of α-phosphoryl sulphoxides, racemic dimethylphosphorylmethyl p-tolyl sulphoxide (1) was prepared and resolved into optical isomers. Sulphoxide (+)-1 with the R chirality at sulphur was synthesized stereospecifically by treatment of (?)-menthyl p-tolylsulphinate with dimethylphosphorylmethyllithium. This communication describes some transformations of optically active 1.     

An Approach to Transfer Methods from HPLC to UHPLC Techniques in Some Carbapenems

Stability-indicating LC methods were developed and validated for the quantitative determination of doripenem, meropenem and tebipenem in the presence of their degradation products formed during forced degradation studies. Isocratic HPLC and UHPLC separations were performed with a core–shell Kinetex 1.7, 2.6 and 5 µm, all C18, 100A, 100 × 2.1 mm columns and the mobile phase composed of acetonitrile and 12 mmol L^?1 ammonium acetate in different ratios. The flow rates of the mobile phase were: 0.5 mL min^?1 for 1.7 µm column, and 1.0 mL min^?1 for 2.6 and 5 µm ones. Detection wavelength was 298 nm and temperature was set at 30 °C. All analysed drugs were exposed to stress conditions which caused their hydrolysis and thermal degradation. The methods were validated by evaluation of linearity, accuracy, precision, selectivity and robustness. Proposed methods were successfully applied for the determination of investigated antibiotics during kinetic studies in aqueous solutions and in the solid state. The advantages of chromatographic procedures which are based on the use of C18 stationary phases with different particle sizes in the analysis of selected carbapenems were discussed.     

Molecular orientation behavior of poly(vinyl chloride) as influenced by the nanoparticles and plasticizer during uniaxial film stretching in the rubbery stage

The structural evolution during uniaxial stretching of poly(vinyl chloride) films was studied using our real time spectral birefringence stretching machine. The effect of clay loading and the amount of plasticizer as well as the rate effects on the birefringence development and true mechanical response are presented with a final model summarizing the molecular phenomena during stretching. Mechano‐optical studies revealed that birefringence correlated with mechanical response (stress, strain, work) nonlinearly. This was primarily attributed to the preexisting strong network of largely amorphous chains connected via small crystallites that act as physical crosslinking points. These crystallites are not easily destroyed during the high‐speed stretching process as evidenced from the birefringence–true strain curves along with the X‐ray crystallinity measurements. At high speeds, the amorphous chains do not have enough time to relax and hence attain higher orientation levels. The crystallites, however, orient more efficiently when stretched at slow speeds. Apparently, some relaxation of the surrounding amorphous chains helps rotate the crystallites in the stretching direction. Overall birefringence is higher at high stretching speeds for a given true strain value. When the nanoparticles are incorporated, the orientation levels are increased significantly for both the crystalline and amorphous phases. Nanoplatelets increase the continuity of the network because they have strong interaction with the amorphous chains and/or crystallites. This in turn helps transfer the local stresses to the attached chains and increase the orientation levels of the chains. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 724–742, 2005     

Effect of montmorillonite content and the type of its modifier on the thermal properties and flammability of polyimideamide nanocomposite fibers

The effects of montmorillonite (MMT) content (1, 3, 5%) and the type of its modifiers on the thermal properties and flammability of PIA nanocomposite fibers have been assessed. Sodium montmorrilonite was modified with aminododecane acid and octadecylamine. Samples of PIA nanocomposite containing commercial MMT: Nanomer PGW from Nanocor were also included in the comparative analysis. It has been found that the glass transition temperature (T _g) of the fibers under investigation depends on the type of MMT’s modifier. On the other hand this parameter does not affect the thermal stability of fibers defined with T ₅ and T ₅₀ indicators since the thermal decomposition of modifiers takes place at lower temperatures.     

Gel Polymer Electrolytes with Talc as a Natural Mineral Filler and a Biodegradable Polymer Matrix in Sodium-Ion Batteries

A gel polymer electrolyte based on poly(vinyl alcohol) (PVA) is used in sodium-ion batteries (SIBs). The use of biodegradable and water-soluble polymer potentially reduces the negative environmental impact. The other components include sodium salt (NaPF₆), sulfolane (TMS) as a plasticizer and talc. For the first time, natural and abundant talc has been used as an inert filler in a gel polymer electrolyte. The best results were obtained for moderate amounts of filler (1 and 3 wt%). Then, an increase in the conductivity, transference numbers, and thermal stability of the membranes was observed. Moreover, the presence of talc had a positive effect on the cyclability of the hard carbon electrode. The discharge capacity after 50 cycles of HC|1 % T_TMS|Na and HC|3 % T_TMS|Na was 243 and 225 mAh g⁻¹, respectively. The use of talc in gel polymer electrolytes containing sodium ions improves the safety and efficiency of SIBs.