Kinetic aspects of bromination of a phthalate-type plasticizer

Abstract

The main characteristics of a complex system of unsaturated plasticizer-bromine using the main "working components" - isomers of 2-ethylhexyl-2-ethylhexene phthalate are considered. It is taken into account that the phthalate-type ester plasticizer is a polar compound with a dipole moment at the level of dioctyl phthalate included in its composition. It has been shown that in the process of bromination, molecular bromine enters into physical interaction with all components of the plasticizer. Dosed introduction of bromine into the system at high stirring speeds leads to the formation of a homogeneous thermodynamically stable system, since the solubility parameters of the components are practically the same. Using a model mixture of bromine-dioctyl phthalate-dibutyl phthalate, it was shown that mixing bromine with plasticizers in any investigated ratios does not lead to the appearance of the boundary “bromine in a plasticizer” or “plasticizer in bromine”. This established the unlimited solubility of bromine in the plasticizer under the conditions of its bromination. Using the method of UV spectroscopy on model mixtures of acetic acid-bromine-water; acetic acid-bromine-hexane, it was proved that in a real system, unsaturated plasticizer-bromine, bromination is most likely carried out only with molecular bromine without the formation of bromine dimers. The mechanism of bromination of unsaturated phthalates included in the plasticizer is shown. A system of kinetic equations in dimensionless variables is proposed. It was found that the nature of the theoretical curves significantly depends on the rate of introduction of bromine with a constant reaction mechanism. A change in the limiting stages of the bromination process was noted depending on the rate of bromine introduction into the system.