V.Kukueva, Ju.Zabulonov

Abstract

The research of elementary reactions occurring in the decomposition of organophosphorus compounds (OPC) has been carried out by ab initio quantum-chemical calculation in the 6-31 G basis set. Rapid elementar reactions with the inhibitor molecule, or its thermal decomposition products, bind active centers of flame, and the removal of any of them by recombination, thereby, reduces their overall concentration. The recombination of radicals leads to a smaller number of hydrogen atoms in the reaction zone, which results in the decrease in chain branching and consequently in the combustion rate as a whole. Such a behavior refers to well-known halogen-containing inhibitors such as HBr, CF₃Br and OPC such as dimethylmethylphosphonate (DMMP).

The performed quantum-chemical calculations made it possible to predict the main thermal decomposition products, as well as probable intermediates. The comparison of the DMMP decomposition energy in the two well-known schemes for the transformation of this substance in the flame showed that in the first stages there is a direct thermal decomposition only at a sufficiently high temperature, therefore, the attack of the inhibitor molecule with active flame radicals should also be taken to account. The results of the quantum-chemical calculations of the Werner-Kool reaction scheme show a significantly greater destruction energy at the first stage of degradation of DMMP, whereas the formation of phosphorus-containing PO₂• radicals, which many researchers recognized as possible traps for the active centers of the flame, occur with less energy. The following controversial issue with regard to intermediates: CH₃PO₂ or (HO)₃РО as a result of a quantum chemical study concluded in favor of the formation of orthophosphate acid by the Korobeynichev mechanism. From this, it is possible to propose the use of not all substances as combustion inhibitors, but formed phosphorus-containing radicals, possibly in the composition of other, less harmful chemical combustion inhibitors, as an example phosphorus containing silica.

 

Key words: inhibition, quantum-chemical calculation, mechanism of chemical reaction, products of destruction.

 

Article

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