Ferrous ion oxygenation

Sung, W. and J. J. Morgan (1980) Kinetics and products of ferrous ion oxygenation in aqueous systems. Envir. Sci. Technol. 14, 561-8. 

Udenfriend reagent A reagent formed from a mixture of ferrous ions, oxygen, ascorbic acid, and ethylenetetraaminetetraacetic acid (EDTA) that is used to oxidise aromatic rings to phenol. 

B. Hydroxylation by Ferrous Ion-Oxygen-Ascorbic Acid 1. The Products of the Reaction... 

Table IV. Hydroxylation of Nitrobenzene by Ferrous Ion—Oxygen System...

Table V. Hydroxylation of Anisole with the Ferrous Ion—Oxygen System Ferrous Sulfate Concentration, 5.0 X lO M...

Solutions of the three isomeric cresols, of similar concentrations to those obtained from reactions on toluene, were oxidized, using the ferrous ion—oxygen system. Isolation of the unreacted cresols showed that the relative reactivity of the three compounds was close to one, and no isomer was selectively oxidized. 

Anisole was hydroxylated by the ferrous ion-oxygen system in the presence of increasing amounts of added ferric ions. This resulted in a decrease rather than an increase in the proportion of m-methoxyphenol (Table XI). 

Table XI. Hydroxylation of Anisole by Ferrous Ion—Oxygen System in the Presence of Ferric Ion...

It is possible that the polar groups play an additional role, i.e., they may assist in orienting the Fe " ions for reaction with O2 molecules. According to Astanina and Rudenko [135], the first step in the Fe(II)-02 reaction mechanism involves the formation of a ferrous ion-oxygen complex ... 

Metal-reducing bacteria, such as those that convert ferric to ferrous ion, have been suggested as an accelerant for steel corrosion in oxygenated waters, lb date, evidence of these bacteria influencing corrosion in industrial systems is scarce. 

This is a simplified treatment but it serves to illustrate the electrochemical nature of rusting and the essential parts played by moisture and oxygen. The kinetics of the process are influenced by a number of factors, which will be discussed later. Although the presence of oxygen is usually essential, severe corrosion may occur under anaerobic conditions in the presence of sulphate-reducing bacteria Desulphovibrio desulphuricans) which are present in soils and water. The anodic reaction is the same, i.e. the formation of ferrous ions. The cathodic reaction is complex but it results in the reduction of inorganic sulphates to sulphides and the eventual formation of rust and ferrous sulphide (FeS). 

When the supply of oxygen is restricted the corrosion product may contain ferrous ions. 

Luminescence reaction. Pholasin undergoes an oxidative luminescence reaction in the presence of any of the following substances Pholas luciferase, ferrous ions, H2O2, peroxidases, superoxide anions, hypochlorite and other oxidants. In all cases, molecular oxygen is required and pholasin is converted into oxypholasin in the reaction. 

As strong metal ion chelators due to their catechol structure, tea flavonoids are able to bind and thus decrease the level of free cellular ferric and ferrous ions, which are required for the generation of reactive oxygen radicals via the Fenton reaction (Yang and Wang, 1993). 

Microsensors have been used to develop profiles in mixed species biofilms. Figure 10 shows concentration profiles of sulfide, oxygen, and pH in a biofilm accumulated on the surface of a mild steel corrosion coupon. The concentration of sulfide is highest near the metal surface, where iron sulfide forms quickly and covers the steel surface if both ferrous and sulfide ions are available. At low ferrous ion concentrations, adherent and temporarily protective films of iron sulfides are formed on the steel surface, with a consequent reduction in corrosion rate. High rates of SRB-induced corrosion of mild steel are maintained only in high concentrations of ferrous ion. 

The formation of hydroxyl or hydroxyl-like radicals in the reaction of ferrous ions with hydrogen peroxide (the Fenton reaction) is usually considered as a main mechanism of free radical damage. However, Qian and Buettner [172] have recently proposed that at high [02]/ [H202] ratios the formation of reactive oxygen species such as perferryl ion at the oxidation of ferrous ions by dioxygen (Reaction 46) may compete with the Fenton reaction (2) ... 

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