Aspects of Homogeneous Catalysis

Another approach is via the peracid route [10,Il], whereby propylene is epoxidized by an organic peracid, usually peracetic acid. The latter is prepared either by reaction of acetic acid with hydrogen peroxide, or by autoxidation of acetaldehyde. - (3) - (4) ---I.... MeC0 H MeCHO +02 3 /'. ° (5) MeC0 H + MeCH=CH ---I .... MeCH-CH + MeC0 H 3 2 2 2 Although this method has been extensively studied [10, II] and is often the method of choice for laboratory scale preparations of epoxides, it has not been widely applied on a commercial scale. The reasons are probably to be found in the hazards associated with the handling of these explosive and corrosive peracids on an industrial scale. Nevertheless, several companies continue to groom this method for future commercialization [12]. With organic hydroperoxides becoming available as commercial chemicals, in the last decade propylene oxide process technology has seen the commercializa tion of the hydroperoxide route. Such a process, developed by Halcon Interna tional and Atlantic Richfield, is that often referred to as the Halcon or Oxirane process [13]. It involves the reaction of propylene with an alkyl hydroperoxide in the presence of a soluble, metal catalyst (usually a molybdenum compound). The alkyl hydroperoxide is prepared by autoxidation of an appropriate hydro carbon. For example, tert-butyl hydroperoxide (TBHP) is prepared by autoxida tion of isobutane. (6) Reaction with propylene gives propylene oxide and tert-butanol as a coproduct.

Inhalt
of Volume 4.- Metal-Catalysed Epoxidations of Olefins with Hydroperoxides.- 1. Introduction.- 2. Metal-Catalysed Epoxidations with Hydrogen Peroxide.- 3. Covalent Metal Peroxides as Epoxidizing Agents.- 4. Metal-Catalysed Epoxidations with Alkyl Hydroperoxides.- 5. Oxidation of other Functional Groups.- 6. Summary.- 7. Glossary of Non-Standard Abbreviations.- 8. References.- Homogeneous Catalytic Reduction of Carbonyl-, Azomethine-, and Nitro-Groups.- 1. Introduction.- 2. Reduction of the Carbonyl Group.- 3. Reduction of Schiff Bases.- 4. Reduction of Nitro-Compounds.- 5. Dihydrogen Evolution.- 6. Reaction Mechanisms.- 7. Conclusions.- 8. Abbreviations for Ligand Names.- 9. References.- Catalysis of Diolefin Reactions by ?3-Allyl Metal Complexes.- 1. Introduction.- 2. Allyl-MT Complexes: Bonding and Dynamic Behaviour.- 3. Oligomerisation, Co-Oligomerisation and Polymerisation of Diolefins.- 4. Relation between Catalyst Structure and Kinetic and Thermodynamic Controls of Butadiene Oligo- and Polymerisation Processes.- 5. Isomerisation of Diolefins.- 6. Heteroactivation of Diolefins.- 7. Conclusions.- 8. References.- Substrates and Phosphorus Ligands Used in Asymmetric Homogeneous Hydrogenations Catalysed by Rhodium Complexes.- 1. Introduction.- Table I: Chiral phosphines used as ligands in the rhodium-catalysed asymmetric hydrogenation.- Table 2: Substrates in the rhodium-catalysed asymmetric hydrogenation.- 2. References.