Oxidation of other alkenes

It has recently been found42 that Au/C and Au/graphite catalysts are effective for the aerobic oxidation of other alkenes at 353 K small amounts of either hydrogen peroxide or tert-butylhydroperoxide ( BuOOH) are needed as oxygen chain initiators. The products of the reactions of cyclohexene, 

Epoxidation of styrene with tBuOOH catalysed by Au/Si02 in the presence of zinc and tetrabutylammonium bromides and carbon dioxide led directly to styrene carbonate at 1 MPa pressure and 353 K, conversion was 90% and selectivity 35%.47 Gold on functionalised polymer also catalyses the reaction of carbon dioxide with various epoxides to give lactones, and with amines to give carbonates.48 

---

The Wacker process is carried out in an aqueous medium containing hydrochloric acid. In addition to ethylene, Smidt and coworkers carried out the oxidation of other alkenes in an acidic aqueous solution of PdCh to prepare carbonyl compoimds. After this report, a few studies on the oxidation of higher alkenes were carried out in organic media. In general, terminal alkenes are converted to methyl ketones rather than aldehydes (equation 1). 

Wilkinson s catalyst has also been utilized for the hydroboration of other alkenes. Sulfone derivatives of allyl alcohol can be hydroborated with HBcat and subsequently oxidized to give the secondary rather than primary alcohol. This reactivity proves to be independent of substituents on the sulfur atom.36 Similarly, thioalkenes undergo anti-Markovnikoff addition to afford a-thioboronate esters.37 The benefits of metal-catalyzed reactions come to the fore in the hydroboration of bromoalkenes (higher yields, shorter reaction times), although the benefits were less clear for the corresponding chloroalkenes (Table 3).38,39 Dienes can be hydroborated using both rhodium and palladium catalysts [Pd(PPh3)4] reacts readily with 1,3-dienes, but cyclic dienes are more active towards [Rh4(CO)i2].40... 

Co-containing POMs have been found to be among the most efficient catalysts for homogeneous aerobic oxidation and co-oxidation processes [91-93]. This prompted many researchers to design solid Co-POM-containing materials [78,94-100]. Thus, various Co-POMs have been deposited on cotton cloth [94] and silica [100], datively [95] or electrostatically [96,97] bonded to NH2-modified silica surfaces (vide infra) as well as intercalated in LDHs [78,98,99]. The resulting materials were successfully used for aerobic oxidation of aldehydes, alkenes, alkanes, alcohols and some other organic substrates. 

On the other hand, Tilley et al. have reported a synthesis of a well-defined tris(tert-butoxy)siloxy-iron(lll) complex [13] as well as respective molecular siloxide complexes of cobalt [14] and copper [15], which appear to become precursors for their grafting onto silica and application as catalysts for oxidation of alkanes, alkenes and arenes by hydrogen peroxide. 

Abstract This chapter covers one of the most important areas of Ru-catalysed oxidative chemistry. First, alkene oxidations are covered in which the double bond is not cleaved (3.1) epoxidation, cis-dihydroxylation, ketohydroxylation and miscellaneous non-cleavage reactions follow. The second section (3.2) concerns reactions in which C=C bond cleavage does occur (oxidation of alkenes to aldehydes, ketones or carboxylic acids), followed by a short survey of other alkene cleavage oxidations. Section 3.3 covers arene oxidations, and finally, in section 3.4, the corresponding topics for aUcyne oxidations are considered, most being cleavage reactions. 

Wacker oxidation. Tsuji et al.s have developed two procedures for oxidation of 1-alkenes to methyl ketones with oxygen that are catalyzed by PdCl2 (7, 278 9, 327). The solvent in both cases is aqueous DMF. One method uses PdCl2-CuCl (molar ratio 1 10) the other uses PdCl2 and p-benzoquinone (molar ratio 1 100). Both procedures are about equivalent for oxidation of simple l-alkenes to methyl ketones, but the former method is usually more effective for oxidation of more complex 1-alkenes. 

Oxidation of Other Arenes. Aromatic compounds with longer alkyl side chains can be converted to ketones or carboxylic acids. All the previously discussed reagents except Cr02Cl2 usually afford the selective formation of ketones from alkyl-substituted arenes. Oxidation with Cr02Cl2 usually gives a mixture of products. These include compounds oxidized in the P position presumably formed via an alkene intermediate or as a result of the rearrangement of an intermediate epoxide.110,705... 

To overcome the problems encountered in the homogeneous Wacker oxidation of higher alkenes several attempts have been undertaken to develop a gas-phase version of the process. The first heterogeneous catalysts were prepared by the deposition of palladium chloride and copper chloride on support materials, such as zeolite Y [2,3] or active carbon [4]. However, these catalysts all suffered from rapid deactivation. Other authors applied other redox components such as vanadium pentoxide [5,6] or p-benzoquinone [7]. The best results have been achieved with catalysts based on palladium salts deposited on a monolayer of vanadium oxide spread out over a high surface area support material, such as y-alumina [8]. Van der Heide showed that with catalysts consisting of H2PdCU deposited on a monolayer vanadium oxide supported on y-alumina, ethene as well as 1-butene and styrene... 

Two possible alcohols might be formed by hydroboration/oxidation of the alkene shown. One product results from addition of BH3 to the top face of the double bond (not formed), and the other product results from addition to the bottom face of the double bond (formed). Addition from the top face does not occur because a methyl group on the bridge of the bicyclic ring system blocks approach of the borane. 

Porphyrin complexes such as (porph)MnCl or (porph)Mn=0 have been much studied for the oxidation of alkanes, alkenes, and other organic compounds using O-transfer agents such as PhIO, H202, or 02. Schiff base complexes have also been used since chiral complexes (e.g., of the salen type) can be readily made on a ton scale and the enantiomers separated in pure forms. Thus the epoxidation... 

The catalytic oxidations of alkanes, alkenes, and other substances are of enormous technological and biological importance. In addition to classical oxidations of unsaturated substances like alkenes and arenes there is an increasing number of systems capable of catalyzing the selective oxidation of saturated hydrocarbons. 

The success of butane selective oxidation inevitably led to testing of vanadium phosphate catalysts for oxidation of other alkanes and alkenes. Pentane has been similarly transformed to phthalic anhydride in addition to MA (91-97). Phthalic anhydride is an important intermediate in the manufacture of plastics. Flowever, the investigation of vanadium... 

Terminal double bonds are selectively oxidized to methyl ketones. A typical procedure for the oxidation of 1-decene to 2-decanone in 65-73% yield with PdCli/CuCl is given in Organic SynthesisAlthough there are several known synthetic methods for methyl ketone preparation, the PdCh-catalyzed oxidation of terminal alkenes seems to be one of the best. In other words, terminal alkenes can be regarded as precursors of methyl ketones, or as masked methyl ketones based on this reaction. This re-... 

However, the oxidation of other steroid alkenes with Cr02X2 (X Cl, F) is affected by the structure of substrates. For example, cholesteryl acetate (22), when treated at -70 to -30 C, produces 3p-acetoxy-5a-chlorocholestan-6-one (23 12%), a mixture of a> and p-cholesteryl acetate epoxides (24 acetoxy>6p-chlorocholestan-6a-ol (25 9%) and 3p-acetoxy-5a-chlorocholestan-63-ol (25 equation 8). 

Oxidation of alcohols typically proceeds in 4-12 h giving excellent yields of carbonyl products. Chromyl chloride, C1O2CI2, like other Cr species, is a vigorous oxidant of organic compounds. It may be, however, tamed as a silica gel adsoibate. This reagent combination is also a good oxidant of alcohols, alkenes and alkynes, that will tolerate halides, esters, lactones, ethers and nitriles. The shelf life of the reagent t pears to be indefinite in the diy state. 

In some cases, oxidations have been placed in another chapter. The oxidation of an alkene to a diol (15-48), and aromatic compound to a diol (15-49), or oxidation to an epoxide (15-50) are placed in Chapter 15, for consistency with the concept of addition to a 7i-bond. Diamination of an alkene (15-53) and formation of aziridines (15-54) are in Chapter 15 for the same reason. Most other oxidations have been placed here. The reactions in this section are classihed into groups depending on... 

In the bulk form, Au is known to be chemically inert compared to the other Pt group metals. However, it has recently been shown that Au clusters, deposited as finely dispersed, small clusters (<5-nm diameter) on reducible metal oxides like Ti02, Fe20s, and C03O4, exhibit catalytic activity with respect to a number of industrially important reactions i.e., CO oxidation, hydrogenation, partial oxidation of hydrocarbons, and selective oxidation of higher alkenes [13,19,25-28,43 5]. This unusual catalytic activity has been shown to be a function of metal cluster size. 

Alkenes are converted to epoxides by oxidation with peroxy acids, and thereby they are protected with regard to certain chemical transformations. Alkaline hydrogen peroxide selectively attacks enone double bonds in the presence of other alkenes. The epoxides can be transformed back to alkenes by reduction-dehydration sequences or using triphenylphosphine, chromous salts, zinc, or sodium iodide and acetic acid. A more advantageous and fairly general method consists, however, of the treatment of epoxides with dimethyl diazomalonate in the presence of catalytic amounts of binuclear rhodium(II) car-boxylate salts. This deoxygenation proceeds under neutral conditions and without isomerization or cy-clopropanation of the liberated alkene (Scheme 97). Furthermore, epoxides can be converted to alkenes with the aid of various metal carbonyl complexes. Thus, they may be nucleophilically opened with... 

Other hand, aim at the formation of useful chemicals, with possible energy recovery or conservation as a bonus (16, 17, 33, 52-54. Thus, complete oxidation of hydrocarbons to COj would yield maximum energy output and is considered to be a fuel cell process. Incomplete, selective oxidation of an alkene to an aldehyde, however, would qualify as an electrogenerative process, since energy is sacrificed for the sake of production of an intermediate oxidation product. 

---