Kinetics and mechanism of the redox reaction of N,N′-phenylenebis-(salicylideneiminato)iron(III) with oxalic acid in mixed aqueous medium

Shallangwa

et al. 2020

Heliyon

The kinetics of reduction of N, N 1 -phenylene bis -(salicylideneiminato)cobalt (III), referred to as [Co(Salophen)] + by L-ascorbic acid (H 2 A) was studied in mixed aqueous medium (DMSO:H 2 O; 1:4 v/v) under pseudo-first-order conditions at 33 ± 1 °C, μ = 0.1 mol dm −3 (NaCl) and λ max = 470 nm. L-ascorbic acid was oxidized to dehydroascorbic acid with kinetics that was first order in both the [H 2 A] and [Co(Salophen) + ] and second-order overall. The reaction involves two parallel reaction pathways; an acid-dependent and the inverse acid-dependent pathways. The inverse acid pathway shows that there is a pre-equilibrium step before the rate determining-step in which a proton is lost. The kinetics followed negative Brønsted–Debye salt effect. Evidence was obtained for the presence of free radicals but none to support the formation of an intermediate complex of significant stability during the reaction. Overall, the data obtained suggest an outer-sphere mechanism for the reaction. A plausible mechanism is proposed.

Section: Resultssupporting

confidence: 65%

Section: Methodsmentioning

confidence: 68%

Section: Introductionmentioning

confidence: 99%

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A kinetic study and mechanisms of reduction of N, N′-phenylenebis(salicyalideneiminato)cobalt(III) by L-ascorbic acid in DMSO-water medium

Abdulsalam

Shallangwa

et al. 2020

Heliyon

“…The reaction rate was found to be inhibited in the presence of added cations while anions catalyzed the reaction rate (Ca 2þ and SO 4 2-, Table 2). Catalysis of added ion suggests that the mechanism of the reaction is outer-sphere (Ibrahim et al, 2019). The formation of a gel was observed on adding acrylamide, which is a radical scavenger, to partially reacted mixture in excess methanol suggesting the presence of free radicals in the reaction (Alioke et al, 2012).…”

Section: Resultsmentioning

confidence: 99%

Reaction of N, N-phenylenebis(salicyalideneiminato)cobalt(III) and l-cysteine in mixed aqueous medium: kinetics and mechanism

Abdulsalam

Shallangwa

et al. 2020

Heliyon

The redox kinetics involving the reaction of N, N 0 -phenylenebis(salicyalideneiminato)cobalt(III) ([CoSalophen] þ ) and l-cysteine (LSH) was studied using pseudo-first order approach under the following conditions,The redox reaction was 1 st order in both [CoSalophen þ ] and [LSH], with the overall 2 nd order. Hydrogen ion concentration effect revealed the activeness of both the protonated and deprotonated form of the reductant, positive Brønsted-Debye salt effect and was also ion catalyzed. There was no evidence suggesting an intermediate complex of significant stability in the reaction. Free radical was detected to take part and as such the reasonable mechanistic pathway for the reaction is suggested to be outer-sphere, hence proposed.

“…The product intermediate complex was examined spectroscopically by scanning the partially reacted mixture at wavelength 400–800 nm, and Michaelis–Menten’s plot of k 1 −1 against [CSH] −1 was equally done [ 30 , 31 ].…”

Section: Methodsmentioning

confidence: 99%

Thermodynamics and Kinetic Investigation of Reaction of Acriflavine with L-cysteine in Aqueous Medium

Nkole

2021

Chemistry Africa

Self Cite

Graphic abstract The kinetic investigation of reaction of 3,6-diamino-10-methylacridin-10-ium chloride (acriflavine) with l-cysteine in aqueous acidic medium at maximum absorption = 460 nm, ionic strength (I) = 0.1 mol dm −3 and temperature (T) = 307 K has been carried out spectrophotometrically. Using a pseudo first order approach, the rate of the redox reaction resulted to first order with respect to the [acriflavine, (AF)] and [l-cysteine, (CSH)] and second order total. Stoichiometric determination confirms that a mole of the acriflavine is consumed by a mole of l-cysteine at a time for the attainment of product formation. The reaction followed a one-way acid independence path. The adjustment in ionic strength (NaCl) and solvent polarity (water/acetone mixture) of the reaction system showed no reasonable effect and there was a fairly decrease in the reaction rate, respectively. The reaction rate is also characterised by neither catalysis nor inhibition of added ions. The negative magnitude of entropy of activation, S ‡ , (− 151.39 ± 031 J mol −1 K −1 ) and positive value of enthalpy of activation, H ‡ , (+ 31.378 ± 030 kJ mol −1 ) suggest that the reaction proceeds via an associative pathway and reasonable energy are needed to lower the activation energy for a tangible products formation. Two acridine unit products polymerised afterward forming a dimer as a result of an intramolecular coupling. A determinable intermediate has been observed through a spectroscopic test and confirmed by Michaelis–Menten’s plot. Based on Taube’s inorganic electron transfer reaction, an inner-sphere mechanistic pathway is implicated with a stable intermediate complex formation as shown below;