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Nature continues to be a rich source of bio-active compounds that often provide the lead for drug development. Isolation and characterization of maoecrystal V, a C19 terpenoid, having potent and selective cytotoxicity towards HeLa cells was recently reported. Unusually complex pentacyclic molecular structure, presence of spirofused rings and several stereogenic centres posed a great synthetic challenge. In this short review, efforts made towards synthesis of maoecrystal V are presented. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

The bulk crosslinking reaction kinetics of a novel two-component waterborne polyurethanes (2K-WPUs) composed of a bio-resin-based polyol dispersion and a hydrophilically modified hexamethylene diisocyanate tripolymer are investigated by freeze-drying and differential scanning calorimetry (DSC) technique at different heating rates. The data fit for the above two components is implemented with the nth-order kinetics equation and Málek's mechanism function method, respectively. The kinetic parameters of crosslinking reaction are determined by the kinetic analysis of the data obtained from the thermal treatment, and then the kinetic model is built. The results indicate that the nth-order model deduced from Kissinger and Crane equation has great distinction with the experimental data, while the Málek analytic mechanism shows that the crosslinking process of the crosslinking reaction follows an autocatalytic reaction. The two-parameter ( m and n) autocatalytic model (S-B model) can well describe the crosslinking reaction process of the studied 2K-WPU. The DSC curves derived from the experimental data show a good agreement with the theoretical calculation under 5-20 °C min heating rate. The results provide theoretical basis for the choice of the manufacturing process and the optimization of processing window. [ABSTRACT FROM AUTHOR]

Relative kinetic techniques have been used to measurethe ratecoefficients for the reactions of oxygenated terpenes (menthol, borneol,fenchol, camphor, and fenchone) and cyclohexanol with hydroxyl radicals(OH) and chlorine atoms (Cl) at 298 ± 2 K and atmospheric pressure.The rate coefficients obtained for the reactions of the title compoundswith OH are the following (in units of 10–11cm3molecule–1s–1): (1.48± 0.31), (2.65 ± 0.32), (2.49 ± 0.30), (0.38 ±0.08), (0.39 ± 0.09) for menthol, borneol, fenchol, camphor,and fenchone, respectively. For the corresponding reactions with Clatoms the rate coefficients are as follows (in units of 10–10cm3molecule–1s–1): (3.21 ± 0.26), (3.40 ± 0.28), (2.72 ± 0.13), (2.93± 0.17), (1.59 ± 0.10), and (1.86 ± 0.29) for cyclohexanol,menthol, borneol, fenchol, camphor, and fenchone, respectively. Thereported error is twice the standard deviation. Product studies ofthe reactions were performed using multipass in situ FTIR (Fouriertransform infrared spectroscopy) and solid-phase microextraction (SPME)with analysis by GC–MS (gas chromatography–mass spectrometry).A detailed mechanism is proposed to justify the observed reactionproducts. [ABSTRACT FROM AUTHOR]

Abstract: This study compares the pyrolysis of cis-2-pinanol to linalool in a mini-channel tubular reactor versus a muti-channel microreactor. The high temperatures (500–650°C) at which the reaction is conducted results in decomposition of linalool to hydroxyolefins (HOL). In the conventional tubular reactor basic additives are required to suppress the side reactions. We have found that higher conversions and selectivities are possible using a microreactor system, without the need for such additives. Experimental data was used to calculate the reaction kinetics and to obtain relative rates of reaction. This information was used for the mathematical modelling studies using MATLAB® and COMSOL®, thus providing a veritable focal point for optimization. Computer simulations using these models showed good concurrence with experimental data thus validating the models and quantifying the experimental procedure. [Copyright &y& Elsevier]

In this work the effect of the overall flow rate of the biphasic reaction mixture on hydrogenation distribution products is reported. As it was already presented by us, the reaction rate strongly correlates with the phase equilibrium existing in the system. On the other hand, carbon dioxide is nonreactive; nevertheless by its presence it changes the energy balance. The catalytic performance in four kinds of overall flow rate conditions (1.3, 3.3, 5.3, and 7.3 mL/min) was compared under fixed hydrogen (2.5 MPa) and total pressure (12.5 MPa). The appearance of isomers of limonene and partially hydrogenated products significantly rely upon the flow rate used in the reaction. The 1% Pd SCN catalyst used in the reaction gave the final products trans- and cis-p-menthane in a 2/3to 1/3molar ratio. [ABSTRACT FROM AUTHOR]

The kinetics of limonene epoxidation catalyzed by PW-Amberlite under triphasic conditions is described. A mechanistic pathway was postulated, and a heterogeneous kinetic model was derived following pseudo-stationary-state theory. Using adsorption parameters that were estimated from independent binary adsorption experiments, the resulting kinetic model fitted the experimental data quite well. [ABSTRACT FROM AUTHOR]

Abstract  The kinetic regularities of the autooxidation of R(+)−limonene (LH) were experimentally studied at various temperatures. A kinetic model including the main elementary reactions and the corresponding rate constants was developed. The degenerate chain branching during limonene oxidation proceeds via bimolecular reactions and involves hydroperoxide LOOH + LH → L· + LO· + H2O and LOOH + LOOH → LO· + LO2 · + H2O. [ABSTRACT FROM AUTHOR]