Hydrocarbon epoxide selectivity

The use of a reactor containing o-dianisidine makes it possible to subtract selectively most of the aldehydes, including a-substituted compounds, but it does not remove ketones (except cyclohexanone), ethers, esters, phenols, olefins and hydrocarbons. Epoxides containing 12 or more carbon atoms in a molecule were subtracted partly or completely. 

The hydrogenolyaia of cyclopropane rings (C—C bond cleavage) has been described on p, 105. In syntheses of complex molecules reductive cleavage of alcohols, epoxides, and enol ethers of 5-keto esters are the most important examples, and some selectivity rules will be given. Primary alcohols are converted into tosylates much faster than secondary alcohols. The tosylate group is substituted by hydrogen upon treatment with LiAlH (W. Zorbach, 1961). Epoxides are also easily opened by LiAlH. The hydride ion attacks the less hindered carbon atom of the epoxide (H.B. Henhest, 1956). The reduction of sterically hindered enol ethers of 9-keto esters with lithium in ammonia leads to the a,/S-unsaturated ester and subsequently to the saturated ester in reasonable yields (R.M. Coates, 1970). Tributyltin hydride reduces halides to hydrocarbons stereoselectively in a free-radical chain reaction (L.W. Menapace, 1964) and reacts only slowly with C 0 and C—C double bonds (W.T. Brady, 1970 H.G. Kuivila, 1968). 

Molybdenum hexacarbonyl [Mo(CO)6] has been vised in combination with TBHP for the epoxidation of terminal olefins [44]. Good yields and selectivity for the epoxide products were obtained when reactions were performed under anhydrous conditions in hydrocarbon solvents such as benzene. The inexpensive and considerably less toxic Mo02(acac)2 is a robust alternative to Mo(CO)6 [2]. A number of different substrates ranging from simple ot-olefms to more complex terpenes have been oxidized with very low catalytic loadings of this particular molybdenum complex (Scheme 6.2). The epoxidations were carried out with use of dry TBHP (-70%) in toluene. 

Epoxides are often encountered in nature, both as intermediates in key biosynthetic pathways and as secondary metabolites. The selective epoxidation of squa-lene, resulting in 2,3-squalene oxide, for example, is the prelude to the remarkable olefin oligomerization cascade that creates the steroid nucleus [7]. Tetrahydrodiols, the ultimate products of metabolism of polycyclic aromatic hydrocarbons, bind to the nucleic acids of mammalian cells and are implicated in carcinogenesis [8], In organic synthesis, epoxides are invaluable building blocks for introduction of diverse functionality into the hydrocarbon backbone in a 1,2-fashion. It is therefore not surprising that chemistry of epoxides has received much attention [9]. 

Together with glutathione conjugation, hydration is a major pathway in the inactivation and detoxification of arene oxides. Exceptions to this rule will be treated when discussing polycyclic aromatic hydrocarbons. Arene oxides are good substrates for microsomal EH, as evidenced in Table 10.1, where hydration of selected arene oxides, alkene oxides, and cy-cloalkene oxides by purified rat liver epoxide hydrolase is compared. The hy- ... 

Co(ni) alkyl peroxides have been prepared and used by Mimoun and coworkers in the hydroxylation of hydrocarbons with this metal a Haber-Weiss type of reactivity is suggested. Square-planar Pt(II) complexes, of the type [(dppe)Pt(CF3)(solv)], used by Strukul in the epoxidation of alkenes and in Baeyer-Villiger oxidations of ketones (Schemes 8 and 9), are effective catalysts also in the direct hydroxylation of aromatics with hydrogen peroxide. The reactivity increases in the presence of electron releasing substituents in the aromatic ring. Ortho and para derivatives are practically the only products observed and interesting selectivity toward the ortho products has been detected (equation 85). 

G.l.c. papers of interest include the classification of 22 acyclic monoterpenoid alcohols according to retention indexes, resolution of cyclic ketones [e.g. ( )-menthone, ( )-isomenthone] as diethyl (+)-tartrate acetals, and the use of lanthanide shift reagents to resolve non-terpenoid racemic epoxides.The occurrence and prevention of monoterpenoid hydrocarbon isomerization during silica gel chromatography has been examined and the separation of monoterpenoids and sesquiterpenoids by gel permeation chromatography is reported. Monoterpenoid hydrocarbons have been selectively extracted from essential oils using dimethylsilicone. ... 

The activity data confirm that an IR absorption band at 960 cm" is a necessary condition for titanium silicates to be active for the selective oxidation of hydrocarbons with aqueous H2O2 as suggested by Huybrechts et al. (9). However, this band is not a sufficient condition for predicting the activity of the TS-1 catalyst. Although TS-l(B) and TS-l(C) show intensities for the 960 cm- band similar to TS-1 (A), their activities are different First of all, the reaction data reveal that TS-1 (A) is much more active than TS-l(B) for phenol hydroxylation, while both samples show similar activity for n-octane oxidation and 1-hexene epoxidation. Therefore, the presence of the IR band at 960 cm-i in TS-1 catalysts may correlate with the activities for the oxidation of n-octane and the epoxidation of 1-hexene but not for phenol hydroxylation. However, note that the amorphous Ti02-Si02 also has an IR absorption band at 960 cm- and it does not activate either substrate. 

As a general rule, the addition of ethylene oxide to a resin backbone will tend to increase the water solubility of the compound. The addition of propylene oxide or butylene oxide to the resin will tend to increase the hydrocarbon solubility of the compound. Often, the dehazer or demulsifier can be made to perform selectively in oil-water systems by adding both ethylene oxide and propylene oxide to the same molecule. Performance and solubility of the alkoxylated compound can then be finely tuned by closely controlling the amount and order of epoxide addition. A random EO-PO based fuel demulsifier is shown in FIGURE 6-6. 

The selective oxidation of hydrocarbons, particularly that of alkanes, remains a challenge. It is not surprising, therefore, that the problems of oxidation processes are addressed in several books,1043-1045 reviews,1046-1057 and a journal special issue,1058 as well as in international conferences1059-1064 devoted to the topic. For the advances in chirally catalyzed oxidation processes, including asymmetric epoxidation and osmylation, Sharpless was one of the recipients of the 2001 Nobel Prize in Chemistry. 

Because the petrochemical industry is based on hydrocarbons, especially alkenes, the selective oxidation of hydrocarbons to produce organic oxygenates occupies about 20% of total sales of current chemical industries. This is the second largest market after polymerization, which occupies about a 45% share. Selectively oxidized products, such as epoxides, ketones, aldehydes, alcohols and acids, are widely used to produce plastics, detergents, paints, cosmetics, and so on. Since it was found that supported Au catalysts can effectively catalyze gas-phase propylene epoxidation [121], the catalytic performance of Au catalysts in various selective oxidation reactions has been investigated extensively. In this section we focus mainly on the gas-phase selective oxidation of organic compounds. 

Oxidations of hydrocarbons (cycloalkanes, cycloalkenes, aromatics) photo-catalyzed by metallotetrapyrroles lead to the formation of epoxides, aldehydes, ketones, alcohols, and carboxylic acids both in solutions and polymer matrices. These processes frequently occur as selective (one-product formation) reactions. Irradiation with visible light has a pronounced accelerating effect on such important industrial processes as the oxidation of thiols to disulfides (Merox process [265]) in a treatment of petroleum distillates or waste water cleaning. 

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