Antioxidant activity and mechanism of inhibitory action of gentisic and α-resorcylic acids

The antioxidant activity of gentisic (GA) and α-resorcylic (α-RA) acids was investigated by considering their molecular structures in various oxidative environments, including DPPH· scavenging assay, stripped olive and soybean oils, and the corresponding oil-in-water emulsions. The mechanism of action in the oils was evaluated in the presence of different concentrations of the antioxidants at 60 °C, using the kinetic parameters the stabilization factor (F), the oxidation rate ratio (ORR), the activity (A), and the average rate of antioxidant consumption ($$\overline{r}_{{{\text{AH}}}}$$ r ¯ AH ). GA was significantly more potent antioxidant than α-RA in all the environments. Although the less polar α-RA showed better activity in the emulsions rather than in the bulk oils, GA with an ortho-hydroxy structure had higher capacity to scavenge DPPH·, and LOO· in the oils and emulsions. The lower performance of α-RA was attributed to its participation in side reactions of chain initiation (AH + LOOH → A· + L· + H2O) and propagation (A· + LH → AH + L·) as competed with the main chain termination reaction (LOO· + AH → LOOH + A·).

Structural and Thermal Properties of Ethylene-Norbornene Copolymers Obtained Using Vanadium Homogeneous and SIL Catalysts

The series of ethylene-norbornene (E-NB) copolymers was obtained using different vanadium homogeneous and supported ionic liquid (SIL) catalyst systems. The 13C and 1H NMR (carbon and proton nuclear magnetic resonance spectroscopy) together with differential scanning calorimetry (DSC) were applied to determine the composition of copolymers such as comonomer incorporation (CNB), monomer dispersity (MD), monomer reactivity ratio (re), sequence length of ethylene (le) and tetrad microblock distributions. The relation between the type of catalyst, reaction conditions and on the other hand, the copolymer microstructure, chain termination reaction analyzed by the type of unsaturation are discussed. In addition, the thermal properties of E-NB copolymers such as the melting and crystallization behavior, like also the heterogeneity of composition described by successive the self-nucleation and annealing (SSA) and the dispersity index (DI) were determined.

Radiation-sensitized Thermal Cracking of n-Butane. I. Radical Reactions

The radiolysis of n-butane was investigated at temperatures ranging from 17 to 548 °C in both static and flow systems.It was concluded that in the radiation-sensitized thermal cracking region the main products, methane, ethane, ethylene, and propylene, were formed by a radical chain mechanism. The conclusion was reached from comparison with the thermal cracking products, the effect of ammonia addition, the dose rate dependence, and in particular the correlation between the temperature change of the type of the main chain-termination reaction and that of the activation energy of propylene formation. The value of the activation energy for propylene formation showed that the main chain-termination reaction at temperatures between 410 and 520 °C was a combination reaction of ethyl radicals. The major part of 1-butene, trans-2-butene, and cis-2-butene, formed in the chain region, was shown to result from the thermal decomposition of the chain carrying butyl radicals.Rate parameters for some of the reactions involved were calculated.

Calculation of reaction order for the homogeneous pyrolysis of organic vapors

A method is proposed for the derivation of a mathematical equation that relates the kinetic parameters of the propagation reactions of homogeneous free-radical chain reactions to the overall order of the reaction. The equation may be used in evaluating the predominant chain-termination reaction, provided that the mechanism of propagation of the chain is well understood. Application of the technique is demonstrated for the pyrolysis of n-butane. It predicts the predominance of the methyl–methyl radical recombination reaction.

The pyrolysis of propylene

Detailed analyses of the reaction products of the pyrolysis carried out in the temperature range 555 to 640°C, at initial pressures between 7 and 300 mmHg, and measurements of overall pressure change have shown that the overall pyrolysis may be described by the expression -d[C 3 H 6 ]/d t = 10 14.06 [C 3 H 6 ] 1.4 exp (-58600/ RT ) mole ml. -1 s -1 . Twenty three primary and three secondary products of the pyrolysis at 600°C and an initial pressure of 103 mmHg have been determined at six extents of reaction up to 12%. On the basis of these measurements a long chain free radical mechanism is proposed in which reactions of the 1-methyl-4-pentenyl radical are of prime importance. The main chain termination reaction is found to be combination of methyl and allyl radicals. It is concluded that radical combination reactions involving allyl are considerably slower than those involving alkyls. Steady-state treatment of the data is precluded by their complexity. Speculative routes to the formation of the many higher products are suggested.

The oxidation of liquid hydrocarbons III. The oxidation of tetralin in the presence of benzoyl peroxide as a free radical chain reaction

The product of the benzoyl peroxide sensitized oxidation of tetralin is the hydroperoxide as it is in the thermal and heavy metal catalysed oxidations. There is clear evidence that the reaction has a chain mechanism. As the concentration of benzoyl peroxide is increased the oxidation rate rises to a constant value which shows that the peroxide both initiates and terminates the reaction chains. The oxidation rate is proportional to the first power of the tetralin concentration and is characterized by a complex less than first order variation with the oxygen pressure over the entire range of peroxide concentrations. This arises from a chain termination reaction with oxygen, a new feature in liquid-phase oxidations and one which is not present in the therm al oxidation. In view of the accepted free radical character of the benzoyl peroxide decomposition this oxygen termination reaction is thought to be characteristic of a free radical chain oxidation. A suggested mechanism gives an expression for the rate identical with that obtained from the kinetic investigation. By using low peroxide concentrations it has been found that the thermal energy chains and the induced free radical chains proceed simultaneously. Decomposition experiments have shown that in oxidizing systems benzoyl peroxide decomposes faster than in solvents in the absence of oxygen. Using this and other kinetic data the oxidation chain length has been found to be approximately 230.