Kinetics and Mechanism of the Oxidation of Vanillin by Hexacyanoferrate(III) in Aqueous Alkaline Medium

Synthesis of keto-biomacromolecule derivatives by oxidation of carboxymethyl cellulose using alkaline hexacyanoferrate (III) for alternative applications in biotechnology

The oxidation kinetics of polysaccharides involving carboxymethyl cellulose (CMC) by several oxidizing agent have been investigated in more detail with shedding some light on the synthesis of their respective keto-derivatives as oxidation precursor products. However, the literature survey indicated that no reports have appeared on the oxidation kinetics of CMC or the synthesis of keto-CMC using hexacyanoferrate (III) ion. Therefore, a lack of information on the transfer of electron process in the rate-determining stage as well as the nature of such keto-derivatives obtained as a result of polysaccharides oxidation using various oxidants in aqueous solutions. Accordingly, the present study presents synthesis of diketo CMC as a biomacromolecule derivative using potassium ferricyanide in alkaline media. The experimental results revealed the formation of either monoketo or diketo-derivatives of CMC based on initial molar ratio between the two reactants. The formation of such keto derivatives was confirmed by the reaction of the oxidation products with both 2,4-dinitrophenyl hydrazine and hydroxyl amine as well as FTIR spectra. The reaction kinetics of oxidation showed unity order in [Fe(CN)₆^3-] and fractional first-orders with respect to both [CMC] and [OH^-].The obedience of the reaction behavior to the Michael-Menten kinetics was indicative to the formation of 1:1 intermediate complex prior to the rate-determining step as a pathway route for oxidation.

Low consumption and portable technology for dithionite detection based on potassium ferricyanide differential spectrophotometry method in related advanced oxidation processes

Carbon neutrality has been received more attention and emerged in wastewater treatment processes. Due to the development of treating technologies with the rising of new-emerging pollutants, the coupled chemical processes also should remain current for the goal of carbon-neutral operation. Among of those updated strategies, several advanced oxidation processes (AOPs) based on dithionite (DTN, S₂O₄^2-), a common water treatment agent, have been established for refractory organic contaminations removal. However, in terms of DTN detection, the traditional formol-titration method has several application limits including the low detection sensitivity and high consumption of formaldehyde. In this study, compared with traditional method, a low energy consumption technology has been developed based on the potassium ferricyanide with the carbon consumption decreasing by about 5 times. Moreover, detection limit of DTN (mmol/L level) also was lower than the titration method. The method was established based on the fact that every 1 mol of DTN can react with 2 mol [Fe(CN)₆]^3- under alkaline condition. According to that potassium ferricyanide (K₃ [Fe(CN)₆]) has the maximum absorption at 419 nm wavelength, a fitting equation based on the linear relationship between the absorbance variation of K₃ [Fe(CN)₆] and DTN amount in the ranges of 0-30 μmol with the detection limit of 0.6 μmol was established with the determination coefficient of 0.99935. It was found that there was no obvious influence of the ubiquitous foreign species with the amount lower than 6 mM, 4 mM, 6 mM, 4 mM and 1 mg/L for Cl^-, HCO₃^-, NO₃^-, SO₄^2- and NOM, respectively. Moreover, methanol and tert-butanol were employed to verify the influence of the presence of organic matters on the determination of DTN and no impact was observed in this study. The proposed method provides a new way for DTN detection with stable and countable performance in the related AOPs with the low electric energy and carbon source consumption and high detection efficiency.

Corrosion protection mechanism of Ce4+/organic inhibitor for AA2024 in 3.5% NaCl

Cerium is a rare earth element that has been widely proposed for the corrosion protection of aluminium alloys (AA). Both cerium salts, Ce³⁺ and Ce⁴⁺, have been used in combination with other compounds to offer synergistic inhibition, however, the inhibitive corrosion mechanism when using Ce⁴⁺ with organic compounds is still not clear. In this study, the synergistic inhibition effect of Ce⁴⁺ and melamine (M) on the corrosion of aluminium alloy 2024 (AA2024) in 3.5% NaCl solution was investigated. Potentiodynamic Polarization (PDP) and Electrochemical Impedance Spectroscopy (EIS) techniques were used to study the synergistic effect of different Ce⁴⁺/M ratios on the corrosion behaviour of AA2024. The PDP study showed that a combination of 50% Ce⁴⁺ and 50% M leads to the lowest corrosion rates, both acting as cathodic inhibitors. Both PDP and EIS results indicated that M or Ce⁴⁺ in isolation did not offer effective corrosion protection, while the combination of M and Ce⁴⁺ significantly enhances the corrosion protection with a synergism parameter equal to 3.5. SEM and EDX observations confirm the findings from the electrochemical techniques. XPS was used to investigate the mechanism of protection, revealing that the reduction of Ce⁴⁺ to Ce³⁺ occurs during protection of AA2024. A new mechanism of corrosion synergistic inhibition by Ce⁴⁺ and organic compounds is postulated where the role of the organic compounds is to enhance the reduction of Ce⁴⁺.

Proposed corrosion protection mechanism of Ce⁴⁺/ organic inhibitor for AA2024.

A Mechanistic Approach to the Influence of Surfactants on the Oxidation of Ethyl Mercaptan and its Dimer Ethyl Mercaptan Disulfide by Hexacyanoferrate(III) Ions in Aqueous Medium

In this paper we report on the rate of oxidation of ethyl mercaptan and its dimer ethyl mercaptan disulfide by alkaline hexacyanoferrate(III) along with its mechanistic pathway, spectrophotometrically. The influence of different experimental parameters, such as change in concentration of EtSH, HCF, OH− and reaction temperature was studdie. It was observed that the order of reaction decreases in [EtSH] or [OH−] from first order to higher concentration, but it certainly did not tend towards zero order. The effect of surfactants on the rate of reaction was observed at the critical micelle concentration (CMC) of the surfactant and reported to be below the CMC. The investigators, thus, concluded that the added products have an insignificant effect on the reaction rate. Further, the activation parameters were evaluated which lend support to the proposed mechanism. The thermodynamic quantities were also determined and the binding parameters have also been evaluated using the Menger and Portnoy model.

Reactivity and stability of selected flavor compounds

Flavor is the most important aspect of food. Based on the complex matrix of the food system and the flavor structure themselves, one important factor that plays a key role in the quality attribute of food is flavor stability. Not surprisingly, there is a large volume of published research investigating the stability of different food flavor compounds, since understanding flavor stability is crucial to creating greater awareness of dietary flavor application. This review presents a variety of factors that are thought to be involved in the stability of several selected important flavor compounds and the approach to improve the stability of different flavors. Some mechanisms of chemical degradation of flavor compounds were also provided.