Istvan Nemes

A possible construction of a complex chemical reaction network

A procedure is suggested for the construction of chemical reaction networks. We define the kinetic communication as a transfer of atoms or atomic groups between two species and determine all the kinetic communications occurring in the possible mechanism of a complex chemical process. The set of kinetic communications is the basis of the communication matrices resulting in the complete network of the overall reaction.Limiting the consideration for certain types of kinetic communications we obtain the reaction subnetworks and selecting arbitrarily species among those participating in the possible mechanism we introduced the concept of the partial subnetworks which correspond to subsets of the complete network.By the simple analysis of the subnetworks it is easy to obtain the sequence network indicating the pathways via which the selected species are formed in the course of the overall process, by the transfer of chosen atoms or atomic groups.

ESR study of the reaction of substituted nitrosobenzenes with aliphatic and saturated alkylaromatic hydrocarbons

We have found that nitrosobenzenes spontaneously react with saturated hydrocarbons in the absence of oxygen and light. For interpretation of this general phenomenon a new reaction pathway has been assumed. In light of these results special care should be taken when applying nitrosobenzenes for inhibition and spin trapping as well as organic synthesis in saturated organic solvents, which are supposed to be inert.AbstractБьло найдено, что в отсутствии кислорода и света насыщенные углеводороды самопроизвольно реагируют с нитрозобензолами. Для интерпретации этого общего явления было предположено новое направление реакции. В свете полученных данных следует обращатя особое внимание при интерпретации экспериментальных результатов в случае применения нитрозобензолов в качестве спиновых ловушек, ингибиторов, а также для синтетических целей при проведении опытов в насыщенных углеводродах как растворителях, которые, по предположению являются инертными.

RECENT APPLICATIONS OF THE KINETIC ISOTOPE METHOD

The kinetics of chemical processes and the theory of simple reactions was developed at the end of the last century. For complex reactions producing highly reactive intermediates that are subsequently consumed, the kinetic treatment is more difficult. Assuming a mechanism that comprises a series of consecutive and parallel elementary steps, we can formulate the corresponding differential equations. Their integration, however, is often impossible. Due to these difficulties, approximate treatments are often applied to the intermediates, such as those based on the Bodenstein stationary concentration principle,’ or the Bodenstein-Semenov principle for degenerate branching chain reactions.’ Though these approximations are useful, their wide application is inhibited hy the lack of analytical data for the intermediates and end-products. Even for thoroughly studied reactions, any additional data bearing on the process generally makes it necessary to formulate a new mechanism and solution of the equation system. This can be illustrated well by several chemical processes discussed in the literature. It became evident in the last decades that there was a need for new methods to avoid the tedious calculations outlined above. Basically, there were two possibilities: (1 ) the detailed and quantitative study of elementary reactions in “artificial” mixtures under experimental conditions where the disturbing effects of other reactions can be excluded and ( 2 ) the in vivo study of elementary steps under “natural” circumstances when the reactions of interest can be investigated separately. An example of the second method is the kinetic application of isotopes.

A possible construction of chemical reaction networks

The chemical reaction networks and the sequence networks represent the pathways of a complex chemical process. In order to study the pathways separately the systematization of the elementary processes included in the possible mechanism is inevitable.This systematization was realized by a special procedure based on linear algebraic methods and enabled us to select the corresponding processes from the possible mechanism. The efficiency of the procedure has been illustrated by its application to the liquid phase oxidation of ethylbenzene and the elementary processes have been selected using a computer program.

On the mechanism of propylene epoxidation catalyzed by molybdenum naphthenate

The mechanism of the catalytic epoxidation of propylene with α-phenylethyl hydroperoxide has been investigated. The epoxidation step is a molecular interaction between propylene and a complex formed from hydroperoxide and catalyst, while part of side products is formed in free radical reactions. This mechanism is valid for the kinetics of both epoxidation and catalytic decomposition of hydroperoxide.AbstractИзучена кинетика каталитического эпоксидирования пропилена гидроперекисью этилбензола. Сама реакция эпоксидирования — это молекулярное взаимодействие между пропиленом и комплексом катализатора с гидроперекисью. Ряд побочных продуктов образуется в радикальных реакциях. Данный механизм описывает кинетику как эпоксидирования так и каталитического разложения гидроперекиси.

A new method for determination of reactivity ratios in hydrocarbon oxidation processes

Abstract A new method has been devised to determine reactivity ratios in hydrocarbon oxidation processes. Reactivity ratio is defined as the ratio of rate constants of the elementary chain propagation processes between the initial hydrocarbon and chain carrier radicals to similar reactions of the hydrocarbon intermediates. The determination is carried out by introducing the intermediate in question in labeled form and subsequently measuring its concentration and radioactivity during the oxidation. It is established that the appropriate equations can be accurately applied to liquid-phase oxidations. In gas-phase oxidations, however, certain difficulties arise when using this procedure. For the application in the latter case the necessary conditions are fulfilled only when chain carrier radicals stemming from the radical isomerization processes possess similar reactivity or when one contributes significantly to the chain propagation. Calculations have been made for six oxidation processes and the corresponding reactivity ratios are reported.