Hydrocarbons hydroxylation catalysts

ROH represents the hydroxylated catalyst. Ri and R represent the ali-phatic or aromatic hydrocarbon residues of the ester. Treatment of rate data, in accordance with the above mechanism, gave the energies and entropies of activation shown in Table 8-9. 

Iodosylbenzene has been used as an effective oxidant in hydrocarbon hydroxylation catalyzed by metal-loporphyrins [687-696]. In particular, various iron(III) and manganese(in) porphyrins can be used as catalysts in hydroxylations of cyclohexane, cyclohexene, adamantane and aromatic hydrocarbons [687,688, 692]. Breslow and coworkers have reported regioselective hydroxylations of several steroidal derivatives catalyzed by metalloporphyrins [689-691]. In a specific example androstanediol derivative 644 was... 

Rigid spirocyclic linking groups can be introduced between porphyrin subunits to provide significant steric restriction to prevent structural relaxation, which in turn helps promote fruitful catalytic properties in PIMs. Phthalocyanine network PIMs are important catalysts for example, iron-porphyrin derivatives can permit the catalysis of hydrocarbon hydroxylations and alkene epoxidations." ... 

Organochromium Catalysts. Several commercially important catalysts utilize organ ochromium compounds. Some of them are prepared by supporting bis(triphenylsilyl)chromate on siUca or siUca-alumina in a hydrocarbon slurry followed by a treatment with alkyl aluminum compounds (41). Other catalysts are based on bis(cyclopentadienyl)chromium deposited on siUca (42). The reactions between the hydroxyl groups in siUca and the chromium compounds leave various chromium species chemically linked to the siUca surface. The productivity of supported organochromium catalysts is also high, around 8—10 kg PE/g catalyst (800—1000 kg PE/g Cr). 

Co-feeding of alcohols effects an increased rate of hydrocarbon formation, as shown in early experiments of Emmett and coworkers1"1 using 14C-labeled alcohols. These experiments were carried out in order to support the hydroxyl-carbene mechanism favored at that time. Their experiments were confirmed by Shi and Davis23 for Co catalysts and co-feeding of ethanol. Furthermore, in their study, the argument that ethanol may be dehydrated to ethene, incorporated, and followed by subsequent chain growth via CH2 insertion could be excluded, as co-fed ethanol incorporated much faster than ethene. 

Finally, it makes possible the oxidation of hydrocarbon to a significant depth, and when the RH molecule contains several methyl groups, the catalyst allows all these groups to be transformed into carboxyls. This last specific feature is insufficiently studied so far. Perhaps, it is associated with the following specific features of oxidation of alkylaromatic hydrocarbons. The thermal decomposition of formed hydroperoxide affords hydroxyl radicals, which give phenols after their addition at the aromatic ring... 

The selective hydroxylation, in the presence of aqueous H2O2, of aromatic hydrocarbons such as benzene, toluene, and xylene to phenol, cresols, and xylenols, respectively, occurs easily on TS-1 (33,165,224). Again, a significant contrast between TS-2 and VS-2 in the oxidation of toluene is that when the catalyst is the former, only aromatic ring hydroxylation takes place, although when the catalyst is VS-2, the side chain C-H bonds are also hydroxylated (165, 218,219,225,226) (Table XXVIII). 

Prior to solving the structure for SSZ-31, the catalytic conversion of hydrocarbons provided information about the pore structure such as the constraint index that was determined to be between 0.9 and 1.0 (45, 46). Additionally, the conversion of m-xylene over SSZ-31 resulted in a para/ortho selectivity of <1 consistent with a ID channel-type zeolite (47). The acidic NCL-1 has also been found to catalyze the Fries rearrangement of phenyl acetate (48). The nature of the acid sites has recently been evaluated using pyridine and ammonia adsorption (49). Both Br0nsted and Lewis acid sites are observed where Fourier transform-infrared (FT IR) spectra show the hydroxyl groups associated with the Brpnsted acid sites are at 3628 and 3598 cm-1. The SSZ-31 structure has also been modified with platinum metal and found to be a good reforming catalyst. 

Whilst this view was widely accepted as explaining many of the observations, a few workers retained for some time a modified version of Hunter and Yohe s direct initiation mechanism to explain a limited range of phenomena. The point at issue is whether the polymerisation of an olefinic hydrocarbon can be initiated by a metal halide alone, without the participation of a co-catalyst, which might be water, a hydroxylic impurity, or a... 

The trans elimination can take place if the basic sites of the alumina attack the hydrogen from one side of the plane and the hydroxyl group is removed from the opposite side of the plane by the acidic sites of the alumina. This may be possible if the reaction occurs within the pores of molecular dimensions (46) or within the crevices of the aluminas. Crevice sites on silica-alumina catalyst have been proposed by Burwell and co-workers (57) on the basis of racemization and exchange reactions of hydrocarbons. 

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). 

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. 

The use of supported metal complexes in transesterification reactions of TGs is not new. An earlier patent claimed that supported metals in a hydroxylated solid could effectively catalyze transesterification. The catalyst preparation used an inert hydrocarbon solvent to attach transition metal alkoxide species to the support surface. The reaction, however, was carried out in the presence of water. The author claimed that water was essential in preparing materials with good catalytic activity. Among the metals employed, titanium catalysts showed the best activity. However, it was not clear from the preparation method if reproducibility could be easily achieved, an important requirement if such catalysts were to be commercially exploited. 

The procedure for preparing supported aluminium chloride relies on the small but significant solubility of aluminium chloride in aromatic hydrocarbons (typically toluene) and the slow reaction of the dissolved A1C13 with the surface hydroxyls of a commercial silica gel or acid-treated clay (Figure 1). One mole equivalent of HC1 is produced during the catalyst preparation consistent with the formation of mostly -OAlCl2 units on the surface and the use of hot solvent is essential so as to force the reaction and to ensure that the HC1 is driven from the system. 

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