Linear alkane hydroxylation

Linear alkanes have been hydroxylated in the 2-, 3-, and 4-positions to give secondary alcohols and ketones in the presence of TS-1 catalyst (216,217) with good selectivities based on alkanes and H2O2 (Table XXIV). 

A linear tetradentate ligand, bpmen [N,N -dimethyl-N,N -bis(2-pyridylmethyl)-l,2-diaminoethane] was reported to allow stereospecific alkane hydroxylation [36, 40], The same holds true for the [Fen(TPA)(CH3CN)2]2+ [TPA = tris(2-pyridylmethyl) amine] catalyst family (Figure 3.3) [35],... 

Linear alkanes yield a mixture of secondary alcohols and ketones (Table 18.2). In methanol, hydroxylation is reduced at more internal positions, while in water and in acetone it occurs randomly. The yield increases with the chain length up... 

The presence of a silica framework with few defects makes TS-1 a highly hydrophobic material suitable for oxidations in the liquid phase with H2O2 as oxidant. Thus, TS-1 has proven to be successful in the oxidation of alcohols, epox-idation of linear olefins, hydroxylation of aromatics, ammoximation of cyclohexanone, oxidation of alkanes to alcohols and ketones, oxidation of amines, oxidation of sulfur-containing compounds, and oxidation of ethers [66-75]. 

These Pd-Ti systems were active in the oxidation of other substrates such as alkanes, alkenes and alcohols. Hexane was hydroxylated into 2- and 3-hexanols, which were further oxidized in part to the corresponding ketones. In this case the product turnover was sensitive to the concentration of HCl. The addition of MeOH was effective as in the case of oxidation by H, , over TS-1. Finally we note that shape selectivity was found in the oxidation of alkanes and alkenes similarly to what was observed for the oxidation where H2O2 was used as oxidant the rates for oxidation of cyclic alkanes and alkenes were much lower than those of linear alkanes and alkenes. 

Porphyrins were first introduced into clays in 1977 by the physical absorption of porphyrin molecules into montmor-illonite in aqueous solutions." The most common examples are the binding of tetracationic M(TMPyP) porphyrins, M = Co(II), Mn(III), Fe(III), into montmor-illonite clays. Co(TMPyP) was the first porphyrin to be intercalated into montmorillonite by ion exchange in acid solution. The interlayer distance expanded from 27 to 37 A upon intercalation. UV-visible studies revealed the retention of cobalt ions in the porphyrin molecules. Mansuy and coworkers have extended this approach and prepared the Mn-porphyrin intercalated materials. These solids are efficient alkene epoxidation and alkane hydroxylation catalysts." Additionally, the catalyst exhibited a marked shape selectivity in favor of small linear alkanes when compared to more bulky substrates. It was also shown that... 

Bartoli, J.F., O. Brigand, P. Battioni, and D. Mansuy (1992). Hydroxylation of linear alkanes catalyzed by iron porphyrins Particular efficacy and regioselectivity of perhalogenated porphyrins. J. Chem. Soc., Chem. Commum. 6, 440 42. 

Hydrogen peroxide in combination with catalysts such as TS-1 acts as a good, "clean" epoxidation system. T e reactions that could be carried with this catalyst include ammoximation of cyclohexanone, epoxidation of propene and other small alkenes, and hydroxylation of aromatics and linear alkanes (Chapter 4). The system produces little waste, avoids the use of hazardous chemicals such as alkyl hydroperoxide, and reduces process complexity. However, the key parameter for industrial development is the cost of H2O2. H2O2 is produced by only a few companies, and very large capital expenditure is required, because H2O2 synthesis (by alkyl-anthraquinone route) is economical only when large quantities are produced. 

The earlier of these studies concentrated on the behavior of water in a model sucrose ester-based water-in-oil (w/o) microemulsion [95]. The behavior of water in w/o microemulsions is of particular importance to the behavior of solutes in the aqueous compartments. The ratio of bulk to free water was examined in microemulsions of this type, comprising sucrose esters and butanol, with linear alkanes as the oil component. Subzero dilferential scanning calorimetry (DSC) was used to show that the hydroxyl groups of the surfactant are the principal determinant of the maximal level of bound or interfacial water and that it is essentially independent of the oil used. Butanol occupies the interface and thereby also influences the water binding capacity. Variation in the chain length of the surfactant induced substantial dilferences in the dilutability of the microemulsions with water, possibly indicating a change in the structure of the microemulsions. 

The octanol/water coefficient (log P) is the standard molecular descriptor used to provide the chemical property of the hydrophobicity of a molecule. Compounds with high partition coefficients usually have very low aqueous solubility. This will decrease the chance of attack by hydroxyl radicals and lead to a lower rate constant. Nevertheless, the linear relationships with log P do not reproduce similar trends of several chemical classes such as alkane and phenol. They could be either positive or negative linear relationships. Alkene (R2 < 0.67), benzene (R2 < 0.78), carboxylic acid (R2 < 0.74), and halide (R2 < 0.55) classes do not provide significant correlations. 

Similar trinuclear carbonyl hydride cluster, Os3(CO)xq (m-H)2 (compound 1.4), catalyzes the oxidation of cyclooctane to cyclooctyl hydroperoxide by hydrogen peroxide in acetonitrile solution [12]. Selectivity parameters obtained in oxidations of various linear and branched alkanes as well as kinetic features of the reaction indicated that the alkane oxidation occurs with the participation of hydroxyl radicals. A similar mechanism operates in the transformation of benzene into phenol and styrene into benzaldehyde. The system also oxidizes 1-phenylethanol to acetophenone. The kinetic study... 

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