Temperature and pH effects on the kinetics of 2-aminophenol auto-oxidation in aqueous solution

Abstract

The kinetics of the auto-oxidation of 2-aminophenol (OAP) to 2-amino-phenoxazin-3-one (APX) was followed in air-saturated aqueous solutions and the in®uence of temperature and pH on the auto-oxidation rate was studied. The kinetic analysis was based on a spectrophotometric method following the increase of the absorbance of APX. The process follows rst order kinetics according to the rate law. The experimental data, within the pH range 4{9.85, were analyzed using both di¬erential and incremental methods. The temperature variation of the overall rate constant was studied at pH = 9.85 within the range 25{50¸C and the corresponding activation energy was evaluated.

Oxidase–peroxidase reaction: kinetics of peroxidase-catalysed oxidation of 2-aminophenol

“…The partial reaction order towards dioxygen also being found equal to one and taking into account Scheme 3 [32,37], we conclude that the rate determining step is the formation of aminophenoxyl radical. The assumption that the reactive oxygen species (ROS) such as HOO Á and H 2 O 2 are released during the auto-oxidation is sustained by literature reported data [37,39] and from observed effects of HRP on OAP oxidation, as it will be shown further. Three significant single reaction steps were added to equation Scheme 1, with the following notations: SH 2 is 2-aminophenol; SH Á is aminophenoxyl radical and P represents the final reaction product, APX.…”

“…It was previously shown that the oxidation of OAP with dioxygen, in di-oxygen saturated solution follows apparent first-order kinetics [39] with respect to substrate concentration (Fig. 1).…”

“…The rate constants used as input data are summarized in Table 1. The rate constant k 1 is assumed to be equal to the apparent first-order constant calculated for OAP auto-oxidation in oxygen-saturated solution, since the formation of HOOÁis the rate-limiting step [39]. The optimum value of k 1 was found (5.48 ± 0.47) 9 10 -5 s -1 with a determination coefficient r 2 = 0.9991 for a significance level a = 0.05.…”

Degradation of the benzoxazolinone class of phytoalexins by Fusarium pseudograminearum, a pathogenic fungus of wheat

“…From a symbiotic rhizophere perspective, phenoxazinone is considered as the final inhibitory compound of benzoxazolinone root exudation Macias et al, 2014). Oxidation of aminophenol to phenoxazinone occurs naturally in aqueous solutions and more rapidly at lower pH (Oancea & Puiu, 2003); in the presence of metallo-reagents, such as cobalt salts (Simandi et al, 1993) or Copper (II) (Puiu et al, 2007); and irradiation with sunlight (Nie & Xu, 2002). As a highly significant inhibitor of weeds and fungal pathogens, phenoxazinones, are considered as part of the inhibitory effects of benzoxazolinones (Gagliardo & Chilton, 1992), and have a significantly higher fungal inhibition, compared to benzoxazolinones .…”

“…(Glenn et al, 2002). As 2-AP oxidization to 2-APO is a spontaneous process (Oancea & Puiu, 2003), the accumulation of 2-APO eventuates from the failure of the FDB2 knockouts to N-malonylate the 2-AP which would otherwise prevent this oxidation. However, in contrast to To investigate the specificity of Fdb2 in detoxification of benzoxazolinone compounds, we further tested the transformants on another indole-derived cereal defence metabolite, 3(dimethyl-amino-methyl)-indole (gramine) (Smith, 1977).…”