Selective reduction and oxidation reactions

Ruinatscha R, Hollrigl V et al (2006) Productivity of selective electroenzymatic reduction and oxidation reactions theoretical and practical considerations. Adv Synth Catal 348 2015-2026... 

It is not intended to give an exhaustive coverage of all possible reduction and oxidation reactions that are of synthetic utility in organic chemistry. Instead, the aim is to give a selection of reactions that will illustrate the major mechanistic pathways. In the case of redox reactions for organic molecules, there is a large number of cases for which the mechanism has not been studied in any detail, or if it has, no consensus has arisen as to the true pathway. This is even true for such an important synthetic reaction as the Clemmensen reduction... 

Aluminum alkoxides, particularly those formed from secondary alcohols, have been of interest to synthetic chemists since the mid-1920s due to their catalytic activity. Examples of these trialkoxides include aluminum isopropoxide (AIP) and aluminum sec-butoxide (ASB). They are easily prepared at lab or plant scale and provide highly selective reductions and oxidations under mild conditions. These reductions are termed Meerwein-Ponndorf-Verley (MPV) reactions after the chemists (1-3) who first investigated their utility. Because a MPV reaction are accuratelybe described as an equilibrium process, the reverse reaction (oxidation) can also be exploited. These associated reactions are termed Oppenauer oxidations (4). Meerwein-Ponndorf-Verley reductions and Oppenauer oxidations as well as other reaction types and applications will be discussed, but first some background is provided concerning structure, preparation, and characterization of aluminum isopropoxide and related compounds. 

High selectivity to H2O and CO2 in order to achieve a complete fuel conversion in the reduction reactions. In the case of low reactivity of the OCs with the fuel, the system needs additional units to process the unconverted fuel and the CO2 capture rate is lower. The high reaction rates for reduction and oxidation reactions are also desirable to reduce the size of the reactors and the possibility to operate in a wide range of operating conditions. 

Reductive and oxidative transformations of small ring compounds form the basis of a variety of versatile synthetic methods which include functionalization and carbon skeleton construction. Redox mechanisms of organotransition metal compounds play an important role in inducing or catalyzing specific reactions. Another useful route in this area is based on one-electron redox reactions. The redox tautomerism of dialkyl phosphonate also contributes to the efficiency of the reductive transformation of small ring compounds. This review summarizes selective transformations which have a high potential for chemical synthesis. 

Electrochemical reduction and oxidation processes offer several advantages over conventional methods in their application to organic synthesis. For example, selective transformations can be carried out on specific groups in a multifunctional, valuable compound under the usually mild reaction conditions. Independence of a reagent will result in drastically diminished environmental problems by spent reagents. Electrochemistry also allows the application of alternative feedstocks and better use of raw materials. Product isolation and continuous processing are simplified. 

Since photogenerated MV" " and Ru(bipy) can be used for water reduction and oxidation respectively, it is tempting to examine a system where the two catalytic processes can take place simultaneously following photoinduced electron transfer. As was pointed out above, the RUO2 and Pt cateOysts have to be active enou to intercept the back reaction. Also, their intervention has to be specific in that MV reacts selectively with the Pt particles while RuCbipy) " " interacts with RUD2. Cross reactions have to be avoided since they lead to short-circuitry of the back reaction. 

---