Oxidation of secondary alcohols byN-methylmorpholine-N-oxide (NMO) catalyzed by atrans-dioxo ruthenium(VI) complex or perruthenate complex: A kinetic study

Abstract: The liquid-phase oxidation of a series of saturated and unsaturated non-allylic alcohols to aldehydes with oxygen or air catalysed by tetra-n-propylammonium perruthenate (TPAP, represented as [(n-Pr)4N]RuO4) at 80–110 °C is shown to proceed with selectivities of 72–91% at 55–80% alcohol conversion. The unsaturated alcohols, such as 9-decenol, 9-octadecenol and β-citronellol, give the corresponding unsaturated aldehydes without competing double bond attack. The time course of oxidation indicates a complex reaction mechanism. The results on oxidation of a test alcohol, t-Bu(Ph)CHOH, suggest that one-electron processes do not play an important role in the TPAP-catalysed aerobic oxidation of alcohols.

Abstract: The Ley–Griffith reaction is utilized extensively in the selective oxidation of alcohols to aldehydes or ketones. The central catalyst is commercially available tetra-n-propylammonium perruthenate (TPAP, n-Pr4N[RuO4]) which is used in combination with the co-oxidant N-methylmorpholine N-oxide (NMO). Although this reaction has been employed for more than 30 years, the mechanism remains unknown. Herein we report a comprehensive study of the oxidation of diphenylmethanol using the Ley–Griffith reagents to show that the rate determining step involves a single alcohol molecule, which is oxidised by a single perruthenate anion; NMO does not appear in rate law. A key finding of this study is that when pure n-Pr4N[RuO4] is employed in anhydrous solvent, alcohol oxidation initially proceeds very slowly. After this induction period, water produced by alcohol oxidation leads to partial formation of insoluble RuO2, which dramatically accelerates catalysis via a heterogeneous process. This is particularly relevant in a synthetic context where catalyst degradation is usually problematic. In this case a small amount of n-Pr4N[RuO4] must decompose to RuO2 to facilitate catalysis.

Abstract: The major goal of the Chapter is to review developments in the use of Ru-porphyrin complexes as homogeneous (or matrix-supported) catalysts for oxygenation and oxidation processes. The subject was given impetus with the discovery of a remarkable reaction in which a Ru(II) porphyrin complex reacted with O2 to give a trans-dioxo-Ru(VI) species. Such species, which can be formed from a wide range of O-atom donors, were shown subsequently to be capable of acting as a bis(monooxygenase) in transferring both the coordinated oxo ligands (as O-atoms) to olefinic substrates, saturated hydrocarbons, phosphines, and thioethers, and the processes become catalytic in the presence of excess of the O-atom donor. Further, the dioxo species can also exhibit oxidase-like activity, and effect stoichiometric or catalytic oxidative-dehydrogenation of phenols, alkoxyarenes, alcohols, and amines. Use of chiral porphyrins has led to catalytic, asymmetric epoxidation and hydroxylations, even though radical intermediates are invoked, as well as oxygenation of racemic substrates (phosphines and more interestingly tertiary alkanes) to yield chiral products by kinetic resolution processes. The reaction mechanisms invoked range from genuine O-atom transfer (from RuVI, RuV, or RuIV species, where the disproportionation reaction [2 O=RuIV⇋RuII+O=RuVI=O] is important), to free-radical induced processes, particularly when the porphyrin ligands are extensively halogenated, as Ru complexes generally of such porphyrins are extremely active in radical-type decomposition of hydroperoxides, often present as trace impurities in hydrocarbon substrates.

Abstract: This chapter introduces the topic and scope of the book and principally concerns the basic preparation, physical and chemical properties of Ru-based ­oxidation catalysts, then summarising the catalytic oxidations which they accomplish. More detail on these is given in the succeeding four chapters. The major oxidants RuO4 (1.2.1), perruthenate [RuO4]− (1.3.1) – mainly TPAP, (nPr4N)[RuO4], ruthenate [RuO4]2− (1.4.1), trans-Ru(O)2(TMP) (1.4.2.5), RuCl2(PPh3)3 (1.9.3) and cis-RuCl2(dmso)4 (1.9.4) are covered in some detail, but many other catalysts are also discussed. In some cases brief comments are made on the mechanisms involved when data on these are given in the cited papers. There is also an Appendix (1.11) which gives brief details on the preparation of four ruthenium oxidation catalysts and selected model oxidations using them.

Abstract: This is one of the most important classes of oxidation effected by Ru complexes, particularly by RuO4, [RuO4]−, [RuO4]2− and RuCl2(PPh3)3, though in fact most Ru oxidants effect these transformations. The chapter covers oxidation of primary alcohols to aldehydes (section 2.1), and to carboxylic acids (2.2), and of secondary alcohols to ketones (2.3). Oxidation of primary and secondary alcohol functionalities in carbohydrates (sugars) is dealt with in section 2.4, then oxidation of diols and polyols to lactones and acids (2.5). Finally there is a short section on miscellaneous alcohol oxidations in section 2.6.

Abstract: Common physical techniques used in purification chemical methods used in purification purification of organic chemicals purification of inorganic and metal organic chemicals general methods for the purification of classes of compounds purification of natural products biochemicals and related products.

Abstract: Tetra-n-butylammonium per-ruthenate (Bun4N)(RuO4) and tetra-n-propylammonium per-ruthenate (Prn4N)(RuO4), with N-methylmorpholine N-oxide, function as mild catalytic oxidants for the high yield conversion of alcohols to aldehydes and ketones and are competitive with more conventional reagents.

Abstract: The results of a mechanistic study using ab initio theoretical methods are used to outline plausible mechanistic sequences for alkane, alcohol, and alkene oxidation by chromyl and molybdyl chlorides. We suggest that the second oxo group is intimately involved in the reaction sequence. This spectator oxo group is suggested to play a central role in stabilizing critical intermediates in these reactions and may be important in other oxidation reactions of metal oxides (Mn042-, OsO,, Ru04, and supported transition metal oxides).

Abstract: Oxidation of steroid alcohols by ruthenium tetroxide gives corresponding ketones in almost quantitative yields. The reaction provides a simple and convenient procedure for converting secondary alcohols to ketones in neutral media. The reconversion of ruthenium dioxide, produced during the oxidation, into the tetroxide with an appropriate oxygen donor such as sodium metaperiodate makes possible the oxidation of a given steroid alcohol to a ketone in the presence of a catalytic amount of ruthenium tetroxide.