Other Oxidation Reactions

Results of a kinetic study of the acid-catalysed oxidation of benzaldehydes by pyri-dinium bromochromate in DMSO have been analysed via several structure-reactivity correlations, and solvent effects have been examined in 19 media. A substantial primary kinetic isotope effect is seen for PhCDO. 

Addition of p-tolyl magnesium bromide to o-benzyl benzonitrile (156), followed by copper-catalysed benzylic oxidation, yields dione (157), via unsubstituted imine (158), in one pot. The imine acts as an intramolecular directing group the formation of the benzoyl is suggested to be triggered by a 1,5-hydrogen transfer with a transient iminyl-copper species. 

Kinetics of the oxidation of formaldehyde, acetaldehyde, and trichloroacetaldehyde by permanganate ion in the presence of iodide have been measured in nitric acid solution.  

The rates of oxidation of six aliphatic aldehydes by tetraethylammonium chlorochro-mate in DMSO are first order in each of oxidant, aldehyde, and hydronium ion. Solvent 

Oxidation of j8-dicarbonyl compounds by f-butyl hydroperoxide in the presence of vanadyl acetylacetonate [VO(acac)2] in benzene results in decomposition of the carbon skeleton, via intermediate trioxo derivatives.  

A rapid self coupling reaction of /i-naphthols occurs in presence ofiron(III) chloride, FeCl3.6H20, using a focused MW oven under solvent-free conditions and is superior to classical heating mode [113]. 

Early data on the mechanism of the reaction of ozone with double bonds of organic compounds have been reviewed [35]. On the basis ofkinetics analysis, itwas suggested that this reaction does not occur by a synchronous addition mechanism but through a reversible stage involving the formation of an intermediate complex of ozone with the double bond. It was suggested that the subsequent stages of the reaction involve the 

Regioselective oxidative coupling of 4-hydroxystilbenes has been investigated [38]. 

It was shown that treating 5-[2-(4-hydroxyphenyl)vinyl]benzene-l,3-diol (resveratrol) with an equimolar amount of silver(I) acetate in dry MeOH at 50 °C for 1 h, followed by chromatographic purification with a short silica gel column, allowed the isolation of its ( )-dehydrodimer, 5-[5-[2-(3,5-dihydroxyphenyl)vinyl]-2-(4-hydroxyphenyl)-2,3-dihydrobenzofuran-3-yl]benzene-l,3-diol, as a racemic mixture in high yield. The present method was applicable to the oxidative dimerization of 4-hydroxystilbenes such as trows-styrylphenol and 5-[6-hydroxy-2-(4-hydroxyphenyl)-4-[2-(4-hydroxyphenyl)-vinyl]-2,3-dihydrobenzofuran-3-yl]benzene-l,3-diol (epsilon-viniferin) leading to the corresponding 2-(4-hydroxyphenyl)-2,3-dihydrobenzofurans possessing various types of biological activities. 

It was reported [39] that osmium tetroxide promoted catalytic oxidative cleavage of ds-stilbene and other olefins. The ds-stilbene catalytic oxidative cleavage gave benzoic acid in 95% yield. The process for the preparation of substituted aromatic and heteroaromatic aldehydes and carboxylic acids by the oxidation of substituted stilbenes has been patented [40]. Stilbenes of various substituents (Ri, R2 = H, Cl-4 alkyl, Cl-4 alkoxy, OH, NO2, CN, COjH, CONH2, SO3H, halogen X = C, N Z = CHO, CO2H  

Oxidation of 4-hydroxystilbenes in methanol using a hypervalent iodine-based oxidant led to the formal 1,2-addition of methoxy groups across the central stilbene 

---

In this manner, a current efficiency of 100% is maintained. Furthermore, since the concentration of Ce + remains at its initial level, the potential of the working electrode remains constant as long as any Fe + is present. This prevents other oxidation reactions, such as that for liiO, from interfering with the analysis. A species, such as Ce +, which is used to maintain 100% current efficiency, is called a mediator. 

Whereas this reaction was used to oxidize ethylene (qv) to acetaldehyde (qv), which in turn was oxidized to acetic acid, the direct carbonylation of methanol (qv) to acetic acid has largely replaced the Wacker process industrially (see Acetic acid and derivatives). A large number of other oxidation reactions of hydrocarbons by oxygen involve coordination compounds as detailed elsewhere (25). 

As with other oxidation reactions, ammoxidation of propylene is highly exothermic, so an efficient heat removal system is essential. 

Ammonia oxidation was a prototype system, but subsequently a number of other oxidation reactions were investigated by surface spectroscopies and high-resolution electron energy loss spectroscopy XPS and HREELS. In the case of ammonia oxidation at a Cu(110) surface, the reaction was studied under experimental conditions which simulated a catalytic reaction, albeit at low... 

Cytochrome P-450. Cytochrome P-450 enzymes consist of a large number of haem-containing mono-oxygenases which catalyze aliphatic and aromatic hydroxylations, epoxidations, as well as other oxidation reactions thus, these enzymes are able to cleave aromatic C-H bonds and also... 

We emphasize that the above results have been observed only in the oxidation of sulfides and phenols, reactions known to follow radical mechanisms. A thorough investigation of the catalytic potential of the materials in other oxidation reactions (epoxidation, hydroxylations, etc.) is warranted. 

Introduction of mesityl groups at the porphyrin ring can prevent the formation of the dimeric products and the reaction with dioxygen now leads to ruthenium(VI)-dioxo complexes of TMP (tetramesitylporphyrin) [35], The tram-Ru(VI)02-TM P species can catalyse the epoxidation of alkenes as well as whole range of other oxidation reactions. After transfer of one oxygen atom to an organic substrate Ru(IV)0-TMP is formed, which disproportionates to an equilibrium of Ru02 and llu ). 

Several other oxidation reactions of selenoxides and telluroxides are summarized in Fig. 23. Ley, Barton, and co-workers discovered that di-4-methoxyphenyltellur-oxide (54) could be used catalytically as an oxidant in the presence of 1,2-dibromotetrachloroethane. After reduction of the telluroxide to the telluride, the di-4-methoxyphenyltelluride (24) debrominated the 1,2-dibromotetrachloroethane to give the tellurium(IV) dibromide, which was hydrolyzed in situ to give the telluroxide 54. This process was used to oxidize phosphines to phosphine oxides and... 

Fig. 23 Other oxidation reactions using delenoxides and telluroxides as mild oxidants.

Table 12.21 Other oxidation reactions catalyzed by zeolites. 

Iodine pentoxide is used for analysis of carbon monoxide and for CO removal from air. It also is used as an oxidizing agent in other oxidation reactions. 

The reactivity of the supported vanadium oxide catalysts for other oxidation reactions also show similar trends as the oxide support is varied from titania to silica [13]. The activity and selectivity for partial oxidation products of vanadium oxide supported on titania being higher than vanadium oxide supported on silica. The oxidation activity of the supported vanadium oxide catalysts is related to the ability to donate oxygen to form the required oxidation products. The... 

This reduction has, of course, to be balanced by the local oxidation reaction. The most likely reaction, oxidation of sulphite, leads to an increase in acidity that would cancel out the rise in pH of Eq. (4.5). Probably other oxidation reactions that do not generate acidity occur that result in a net increase in pH (an example would be photocorrosion of the CdSe by photogenerated holes). 

Phillips (P2) has studied the radiation reactions of sugars in dilute solution and reported a preferential oxidation occurring at the C 6 position, which results in conversion of the glucose to glucuronic acid. Other oxidizing reactions resulting in the formation of aldehyde offer alternative pathways. 

The present chapter will primarily focus on oxidation reactions over supported vanadia catalysts because of the widespread applications of these interesting catalytic materials.5 6,22 24 Although this article is limited to well-defined supported vanadia catalysts, the supported vanadia catalysts are model catalyst systems that are also representative of other supported metal oxide catalysts employed in oxidation reactions (e.g., Mo, Cr, Re, etc.).25 26 The key chemical probe reaction to be employed in this chapter will be methanol oxidation to formaldehyde, but other oxidation reactions will also be discussed (methane oxidation to formaldehyde, propane oxidation to propylene, butane oxidation to maleic anhydride, CO oxidation to C02, S02 oxidation to S03 and the selective catalytic reduction of NOx with NH3 to N2 and H20). This chapter will combine the molecular structural and reactivity information of well-defined supported vanadia catalysts in order to develop the molecular structure-reactivity relationships for these oxidation catalysts. The molecular structure-reactivity relationships represent the molecular ingredients required for the molecular engineering of supported metal oxide catalysts. 

The above studies with methanol oxidation over the different supported vanadia catalysts demonstrated the dramatic effect of the specific oxide support on the reaction TOF, approximately four orders of magnitude for methanol oxidation. Several other oxidation reactions over the same series of supported vanadia catalysts were also investigated to determine if the effect of the oxide support is a general phenomenon, and the results are listed in Table 2. 

While the effect of crystallite size has been investigated for reactions on iron oxide, the dependence of the activity and selectivity of other oxidation reactions on the nature of the exposed surface planes has been investigated for reactions on Mo03 and V2Os catalysts. A list of these reactions, the catalysts used, and the major conclusions are listed in Table IX. It appears that all the reactions listed are structure sensitive, that is, different crystal faces catalyze different reactions, or special active sites are required. 

The use of certain vanadium compounds as catalysts has been increasing. Vanadium oxy trichloride is a catalyst in making ediylene-propylene rubber. Ammonium metavanadate and vanadium pentoxide aie used as oxidation catalysts, particularly in the production of polyamides, such as nylon, in the manufacture of H>S04 by the contact process, in the production of phdialic and maleic anhydrides, and in numerous other oxidation reactions, such as alcohol to acetaldehyde, anthracene to anthraquinone, sugar to oxalic acid, and diphenylamine to carbazole. Vanadium compounds have been used for many years 111 die ceramics field for enamels and glazes. Colors are produced by various combinations of vanadium oxide and silica, zirconia, zinc, lead, tin, selenium, and cadmium. Vanadium intermediate compounds also are used in the making of aniline Mack used by the dye industry... 

Indeed, tungsten carbide (WC) was the first transition metal carbide shown to be active for the hydrogen oxidation reaction,1 and this was followed by numerous reports of the reactivity of carbides in other oxidation reactions (for reviews, see References 2-4). 

Many titanium silicates are active for this reaction, Ti-beta and Ti-HMS being the most active. The results demonstrate that in catalysis by TS-1 and by medium-pore zeolites, the reaction is limited by diffusion. TS-48, which has been found to be inactive in other oxidation reactions, is an active catalyst for the oxidation of aniline (Gontier et al, 1994 Sonawane et al., 1994). 

In all reactions, wood of white fir Abies concolor) has been used. For the alkaline nitrobenzene reactions, extractive-free —20+40 mesh heart-wood sawdust containing 28.0% Klason lignin was used. Sequential extraction of the original sawdust with alcohol-benzene, 95% ethanol, and hot water gave extractives amounting to 4.9, 0.5, and 1.2%, respectively. In the other oxidation reactions, nominal 5 -in. wood chips, commonly used in pulping procedures, were employed. The mixed sap wood-heart-wood chips contained 26.5% Klason lignin and sequential extractives of 3.3, 0.5, and 3.2%, respectively. 

---