Kinetics
and Mechanism of <sup>•</sup>OH Mediated
Degradation of Dimethyl Phthalate in Aqueous Solution: Experimental
and Theoretical Studies
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Abstract
The hydroxyl radical (<sup>•</sup>OH) is one of the main
oxidative species in aqueous phase advanced oxidation processes, and
its initial reactions with organic pollutants are important to understand
the transformation and fate of organics in water environments. Insights
into the kinetics and mechanism of <sup>•</sup>OH mediated
degradation of the model environmental endocrine disruptor, dimethyl
phthalate (DMP), have been obtained using radiolysis experiments and
computational methods. The bimolecular rate constant for the <sup>•</sup>OH reaction with DMP was determined to be (3.2 ±
0.1) × 10<sup>9</sup> M<sup>–1</sup>s<sup>–1</sup>. The possible reaction mechanisms of radical adduct formation (RAF),
hydrogen atom transfer (HAT), and single electron transfer (SET) were
considered. By comparing the experimental absorption spectra with
the computational results, it was concluded that the RAF and HAT were
the dominant reaction pathways, and OH-adducts (<sup>•</sup>DMPOH<sub>1</sub>, <sup>•</sup>DMPOH<sub>2</sub>) and methyl
type radicals <sup>•</sup>DMP(-H)α were identified as
dominated intermediates. Computational results confirmed the identification
of transient species with maximum absorption around 260 nm as <sup>•</sup>DMPOH<sub>1</sub> and <sup>•</sup>DMP(-H)α,
and these radical intermediates then converted to monohydroxylated
dimethyl phthalates and monomethyl phthalates. Experimental and computational
analyses which elucidated the mechanism of <sup>•</sup>OH-mediated
degradation of DMP are discussed in detail