Redox hydration

Redox hydration or oxygenation under reductive conditions... 

Studies on the mechanism of other olefin oxygenations, such as allylic oxidation, glycol formation and redox hydration can be expected in the near future. 

The data in Tables 4.2 and 4.3 refer to ions in aqueous acid solution for cations, this means effectively [MlHjO), ]" species. However, we have already seen that the hydrated cations of elements such as aluminium or iron undergo hydrolysis when the pH is increased (p. 46). We may then assume (correctly), that the redox potential of the system... 

In an aquo-complex, loss of protons from the coordinated water molecules can occur, as with hydrated non-transition metal ions (p. 45). To prevent proton loss by aquo complexes, therefore, acid must usually be added. It is for these conditions that redox potentials in Chapter 4 are usually quoted. Thus, in acid solutions, we have... 

The ricji oxoacid chemistry of sulfur (pp. 705-21) is not paralleled by the heavier elements of the group. The redox relationships have already been summarized (p. 755). Apart from the dark-brown hydrated monoxide Po(OH)2 , which precipitates when alkali is added to a freshly prepared solution of Po(ll), only compounds in the +4 and +6 oxidation states are known. 

Figure 30.3 Variation with atomic number of some properties of La and the lanthanides A, the third ionization energy (fa) B, the sum of the first three ionization energies ( /) C, the enthalpy of hydration of the gaseous trivalent ions (—A/Zhyd)- The irregular variations in I3 and /, which refer to redox processes, should be contrasted with the smooth variation in A/Zhyd, for which the 4f configuration of Ln is unaltered.

The standard redox potential is 1.14 volts the formal potential is 1.06 volts in 1M hydrochloric acid solution. The colour change, however, occurs at about 1.12 volts, because the colour of the reduced form (deep red) is so much more intense than that of the oxidised form (pale blue). The indicator is of great value in the titration of iron(II) salts and other substances with cerium(IV) sulphate solutions. It is prepared by dissolving 1,10-phenanthroline hydrate (relative molecular mass= 198.1) in the calculated quantity of 0.02M acid-free iron(II) sulphate, and is therefore l,10-phenanthroline-iron(II) complex sulphate (known as ferroin). One drop is usually sufficient in a titration this is equivalent to less than 0.01 mL of 0.05 M oxidising agent, and hence the indicator blank is negligible at this or higher concentrations. 

A major advantage of redox polymers is their ability to form hydrated films with very high mediator concentration so that there is good electronic contact between the redox polymer and a large number of trapped enzyme molecules, regardless of... 

It is well known that Rh(I) complexes can catalyze the carbonylation of methanol. A heterogenized catalyst was prepared by ion exchange of zeolite X or Y with Rh cations.126 The same catalytic cycle takes place in zeolites and in solution because the activation energy is nearly the same. The specific activity in zeolites, however, is less by an order of magnitude, suggesting that the Rh sites in the zeolite are not uniformly accessible. The oxidation of camphene was performed over zeolites exchanged with different metals (Mn, Co, Cu, Ni, and Zn).127 Cu-loaded zeolites have attracted considerable attention because of their unique properties applied in catalytic redox reactions.128-130 Four different Cu sites with defined coordinations have been found.131 It was found that the zeolitic media affects strongly the catalytic activity of the Cd2+ ion sites in Cd zeolites used to catalyze the hydration of acetylene.132... 

Although the redox reaction mechanisms of iridium oxide are still not clear, most researchers believe that the proton exchange associated with oxidation states of metal oxides is one of the possible pH sensing mechanisms [41, 87, 100, 105], During electrochemical reactions, oxidation state changes in the hydrated iridium oxide layer are... 

M. Kanungo and M.M. Collinson, Diffusion of redox probes in hydrated sol-gel-derived glasses. Effect of gel structure. Anal. Chem. 75, 6555-6559 (2003). 

Rh was loaded by incipient wetness impregnation. SRE reaction over these catalysts revealed that ethanol hydration is favorable over acidic or basic catalysts while dehydrogenation is favorable over redox catalysts. Among the catalysts, a 2%Rh/Ceo.8Zro.202 exhibited the best performance, may be due to strong Rh-support interaction... 

Iron(III) very readily forms complexes, which are commonly 6-coordinate and octahedral. The pale violet hexaaquo-ion [Fe(H20)6]3+ is only found as such in a few solid hydrated salts (or in their acidified solutions), for example Fe2(S04)3.9H20. Fe(C104)3.10H20. In many other salts, the anion may form a complex with the iron(III) and produce a consequent colour change, for example iron(III) chloride hydrate or solution, p. 394. Stable anionic complexes are formed with a number of ions, for example with ethanedioate (oxalate), C204, and cyanide. The redox potential of the ironll ironlll system is altered by complex formation with each of these ligands indeed, the hexacyanoferrate(III) ion, [Fe(CN)6]3. is most readily obtained by oxidation of the corresponding iron(II) complex, because... 

Non-redox reactions where water is formed as a product are reactions of dehydration. Such reactions can occur between two substrate molecules, or they can involve two functional groups in a single substrate, either creating a new bond (e.g., lactone formation), or transforming a single into a double bond. In xenobiotic metabolism, dehydration is usually in dynamic equilibrium with hydrolysis or hydration and is of relatively modest significance (Chapt. 11). 

---