The antioxidant activity, in terms of radical scavenging capacity, of altogether 15 different lignans was measured by monitoring the scavenging of the free radical 2,2-diphenyl-1-picrylhydrazyl (DPPH). The effect of differences in skeletal arrangement or the degree of oxidation of the lignans was investigated in a structure-activity relationship study. A large variety in the radical scavenging capacities of the different lignans was observed and related to some structural features. Lignans with catechol (3,4-dihydroxyphenyl) moieties exhibited the highest radical scavenging capacity, while the corresponding guaiacyl (3-methoxy-4-hydroxyphenyl) lignans showed a slightly weaker scavenging capacity. In addition, the butanediol structure was found to enhance the activity, whereas a higher degree of oxidation at the benzylic positions decreased the activity. Additionally, the readily available lignans (-)-secoisolariciresinol, a mixture of hydroxymatairesinol epimers and (-)-matairesinol were studied in more detail, including kinetic measurements and identification of oxidation products in the reactions with DPPH and ABAP (2,2-azobis(2-methylpropionamidine) dihydrochloride. The identification of reaction products, by GC-MS, HPLC-MS and NMR spectroscopy, showed that dimerisation of the two aromatic moieties was the major radical termination reaction. Also, the formation of adducts was a predominant reaction in the experiments with ABAP. The kinetic data obtained from the reactions between the lignans and DPPH indicated a complex reaction mechanism.

The migration of acetyl, pivaloyl, and benzoyl protective groups and their relative stabilities at variable pH for a series of beta- d-galactopyranoses were studied by NMR spectroscopy. The clockwise and counterclockwise migration rates for the different ester groups were accurately determined by use of a kinetic model. The results presented provide new insights into the acid and base stabilities of commonly used ester protecting groups and the phenomenon of acyl group migration and may prove useful in the planning of synthesis strategies.

Direct catalytic valorization of bioethanol to 1-butanol over different alumina supported catalysts was studied. Thirteen (13) heterogeneous catalysts were screened in search for the optimal material composition for direct one-pot conversion of ethanol to 1-butanol. For the most promising catalyst, a 25% ethanol conversion with 80% selectivity (among liquid carbon products) to 1-butanol could be reached at 250 °C. Additionally, the reaction kinetics and mechanisms were further investigated upon use of the most suitable catalyst candidate. OPEN ACCESSCatalysts 2012, 2 69

Epoxidation of cottonseed oil by peroxyformic acid (PFA) was studied in a semibatch calorimeter. This liquid-liquid reaction system is composed of different exothermic steps. Thus, a kinetic modeling strategy to diminish the number of parameters to estimate was developed by investigating each reaction system: PFA synthesis and decomposition, ringopening and epoxidation. A thermal study was conducted by determining heat capacity of the different organic species, and by analyzing the evolution of global heat-transfer coefficient with the reaction extent. The epoxidation reaction was performed in a semibatch reactor under isoperibolic mode within an initial temperature range of 50-708C, an organic phase of 30-34 wt %, a formic acid molar flow rate of 0.02-0.05 mol/min and an addition time of 25-50 min. The interfacial mass transfer was supposed to be faster than the intrinsic reaction kinetics suppressing the use of mass transfer correlation. Nonlinear regression was used to estimate the kinetic and thermal parameters. The kinetic parameters of epoxidation of the three different fatty acids, namely oleic, linoleic, and its intermediate were estimated. The reaction enthalpy of epoxidation was estimated to 2230 6 3.8 kJ/mol, and the reaction enthalpy of ring-opening was measured to be 290 kJ/mol by Tian-Calvet calorimeter.Kinetic modeling of vegetable oils epoxidation by peroxycarboxylic acids formed in situ in batch and semibatch reactor system has been described by several research groups. This system is complex due to the presence of several consecutive steps. Different approaches have been done such as:Taking into account mass transfer parameters using different correlations or by estimating them, this model is called two-phase kinetic model. Frequently, only carboxylic and peroxycarboxylic acids mass-transfer coefficients were taken into account. [24][25][26] Pseudohomogeneous model by assuming fast mass transfer compared to reaction kinetics, this leads to a simplification of the mass balance equations. [27][28][29][30][31][32] Establishing the mass balance only on the organic phase and assuming steady-state approach on peroxycarboxylic acids formation. 13,[33][34][35][36][37][38][39][40] The advantage of that approach is that graphical method can be used to determine epoxidation rate constants, but one neglects ring-opening reaction. This model is called homogeneous model.Some authors have focused their study only on the ringopening reactions system in batch or semibatch reactor. One can distinguish the two following approaches:Only considering the organic phase and using a pseudofirst-order approach. 41-43 Figure 1. Simplified mechanism of the Prileschajew oxidation of vegetable oils.

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The kinetics of the glycerol oxidation using a carbon supported gold catalyst was studied experimentally in a batch reactor at oxygen pressures up to 10 bar and at temperatures from 25 to 100°C. The influence of the mass transfer on the reaction was estimated and confirmed with theoretical calculations. A kinetic model has been proposed on the basis of a Langmuir-Hinshelwood mechanism for the experiments carried out in the kinetic regime and the kinetic parameters (reaction rate and adsorption constants as well as activation energies) were calculated. diffusion coefficient [m 2 /s]; D eff : effective diffusion coefficient [m 2 /s]; e: rate of flow energy supply per unit mass of liquid [m 2 /s 3 ]; E A : activation energy [J/mol]; Fr: Froude number [)]; H i : Henry´s coefficient [kPa m 3 /mol]; k 1 ... k 6 : reaction rate constants [L ðn i þn bi À1Þ /(mol n i þn bi À1 min g)]; k 01 ... k 06 : pre-exponential factors [L ðn i þn bi À1Þ /(mol n i þn bi À1 min g)]; K 1 ... K 6 : adsorption equilibrium constants [l/mol]; k l : gas-liquid mass transfer coefficient [cm/s]; k l a: volumetric gas-liquid mass transfer coefficient [s )1 ]; k s : liquid-solid mass transfer coefficient [cm/s]; n 1 ... n 6 : reaction order with respect to the educt of step 1 ... 6 [)]; n b : reaction order with respect to the base concentration [)]; N: speed of agitation [Hz]; N P : power number [)]; P: oxygen pressure [kPa]; r 1 ... r 6 : reaction rates of respective steps in figure 1 [mol/L min]; Re: Reynolds number [)]; Sc: Schmidt number [)]; V: reaction volume [m 3 ]; V s : superficial gas velocity [cm/s]; w: catalyst amount [g]Greek Letters: a l : ratio chemical reaction/gas-liquid mass transfer [)]; a s : ratio chemical reaction/liquid-solid mass transfer [)]; / exp : Thiele modulus [)]; : catalyst porosity [)]; l: viscosity of the liquid [g/cm s]; m: kinematic viscosity [cm 2 /s]; r: surface tension [g/s 2 ]; q: density of the liquid [g/cm 3 ]; w: shape factor [)]; s: catalyst tortuosity [)]; x: ratio catalyst weight to reactor volume [kg/m 3 ]

Acetylated oligosaccharides are common in nature. While they are involved in several biochemical and biological processes, the role of the acetyl groups and the complexity of their migration has largely gone unnoticed. In this work, by combination of organic synthesis, NMR spectroscopy and quantum chemical modeling, we show that acetyl group migration is a much more complex phenomenon than previously known. By use of synthetic oligomannoside model compounds, we demonstrate, for the first time, that the migration of acetyl groups in oligosaccharides and polysaccharides may not be limited to transfer within a single monosaccharide moiety, but may also involve migration over a glycosidic bond between two different saccharide units. The observed phenomenon is not only interesting from the chemical point of view, but it also raises new questions about the potential biological role of acylated carbohydrates in nature.

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