Unusual kinetic role of a water‐soluble iron(III) porphyrin catalyst in the oxidation of 2,4,6‐trichlorophenol by hydrogen peroxide

Abstract

The oxidation of 2,4,6-trichlorophenol (TCP) to 2,6-dichloro-1,4-benzoquinone (DCQ) by hydrogen peroxide using iron(III) meso-tetra(4-sulfonatophenyl) porphine chloride, Fe(TPPS)Cl, as a catalyst was studied with stopped-flow UV-vis spectrophotometry and potentiometry using a chloride ion selective electrode. The observations are interpreted by a threestep kinetic model: the initial reaction of the catalyst with the oxidant (Fe(TPPS) + + H 2 O 2 → Cat ) produces an active intermediate, which oxidizes the substrate (Cat + TCP → Fe(TPPS) + + DCQ + Cl − ) in the second step. The third step is the transformation of the catalyst into a much less active form (Cat → Cat ) and is responsible for the unusual kinetic phenomena observed in the system. C

Kinetic Analysis of a Naturally Occurring Bioremediation Enzyme: Dehaloperoxidase-Hemoglobin from Amphitrite ornata

“…The decrease in absorbance on time scales of 50 s and longer is due to secondary hydrolysis reactions of the 2,6-DCQ product. 36 Because of the secondary reaction, only the short time kinetics were used to estimate the catalytic rate for the process. This choice is consistent with the common practice of confining analysis of Michaelis-Menten kinetics to the initial rates.…”

“…36 This type of behavior also suggests that the electron transfer from substrate to catalyst (i.e., heme iron or tyrosine) is not rate limiting. The catalyst concentration may be a limiting reagent due to diffusion control as well as other factors such as inactivation by conversion to a less active form.…”

Light-induced multistep redox reactions: The diode-array spectrophotometer as a photoreactor

“…The possibility of the systematic use of a diode-array spectrophotometer as a photochemical device was demonstrated on the aqueous photoreaction of DCQ [7], which is an important process in the destructive chemical oxidation of chlorophenols [14][15][16]. The photochemical reaction itself is known from the previously studied chemistry of other quinones [17][18][19].…”

Dimorphite-DL: an open-source program for enumerating the ionization states of drug-like small molecules

“…Adding hydrocarbon substituents to the phenyl ring increases the hydroxyl pK a (e.g., m -cresol, 4-( tert -butyl)phenol, and 2,6-di- tert -butyl-4-methyl-phenol have pK a values of 10.09 [24], 10.32 [25], and 12.55 [26], respectively). In contrast, halide substituents tend to decrease the hydroxyl pK a (e.g., 2,3,4,5,6-pentachlorophenol, 2,4,6-trichlorophenol, 2,4-dichlorophenol, and 4-chlorophenol have pK a values of 4.79 [27], 6.15 [28], 7.85 [29], and 9.59 [25], respectively). Dimorphite-DL considers only the phenol substructure when predicting ionization states.…”