Hexane aliphatic oxidation

This chapter reports about an investigation on the catalytic gas-phase armnoxidation of u-hexane aimed at the production of 1,6-Ce dinitriles, precursors for the synthesis of hexamethylenediamine. Catalysts tested were those also active and selective in the ammoxidation of propane to aciylonitrile mtile-type V/Sb and SnA /Nb/Sb mixed oxides. Several A-containing compounds formed however, the selectivity to cyano-containing aliphatic linear Ce compounds was low, due to the relevant contribution of side reactions such as combustion, cracking and formation of heavy compounds. 

Lageveen et al. [41] showed that the monomer composition of aliphatic saturated poly(3HAMCL) produced by P. oleovorans is depended on the type of n-alkane used. It appeared that the n-alkanes were degraded by the subsequent removal of C2-units and it was therefore proposed that the /1-oxidation pathway was involved in poly(3HAMCL) biosynthesis. Preusting et al. [42] confirmed these results but also showed that with hexane as substrate some 3-hydroxyoctanoate and 3-hydroxydecanoate were produced, indicating that additional pathways were involved in poly(3HAMCL) biosynthesis (Table 1). 

The oxidation of 2-ethylhexan-l-ol to 2-ethyl-hexanal by the Oppenauer oxidation with aliphatic aldehydes such as acetaldehyde, propionaldehyde, and isobutyr-aldehyde has been investigated with gas-phase reactants and MgO as the catalyst (196). Reaction with propionaldehyde was found to be an effective synthetic route for 2-ethylhexanal preparation, whereas with acetaldehyde and isobutyraldehyde a gradual catalyst deactivation in a flow reactor was observed. 

Products of the LOX pathway or compounds formed by autoxidation of fatty acids (Scheme 7.2) are also important for leek aroma [31, 163]. Volatile compounds of the LOX pathway are not pronounced in the aroma profile of freshly cut leeks owing to a high content of thiosulfinates and thiopropanal-S-oxide [30]. In processed leeks that have been stored for a long time (frozen storage), however, these aliphatic aldehydes and alcohols have a greater impact on the aroma profile owing to volatilisation and transformations of sulfur compounds [31, 165]. The most important volatiles produced from fatty acids and perceived by GC-O of raw or cooked leeks are pentanal, hexanal, decanal and l-octen-3-ol (Table 7.5) [31, 35, 148, 163, 164]. 

Aliphatic hydroxylation. As well as unsaturated aliphatic compounds such as vinyl chloride mentioned above, which are metabolized by epoxidation, saturated aliphatic compounds also undergo oxidation. The initial products will be primary and secondary alcohols. For example, the solvent n-hexane is known to be metabolized to the secondary alcohol hexan-2-ol and then further to hexane-2,5-dione (Fig. 4.9) in occupationally exposed humans. The latter metabolite is believed to be responsible for the neuropathy caused by the solvent. Other toxicologically important examples are the nephrotoxic petrol constituents, 2,2,4- and 2,3,4-trimethylpentane, which are hydroxylated to... 

Oxidation of alcohols. 1 Secondary alcohols are oxidized to carbonyl compounds by Clayfen in pentane or hexane under vigorous stirring. Primary benzyl alcohols are oxidized satisfactorily, but primary aliphatic alcohols are oxidized to complex mixtures. Isolated yields are generally>80%. Nitrite esters (RONO) have been identified as intermediates. 

Aliphatic Hydroxylation. Simple aliphatic molecules such as -butane, -pentane, and n-hexane, as well as alicylcic compounds such as cyclohexane, are known to be oxidized to alcohols. Likewise alkyl side chains of aromatic compounds such as cyclohexane, are known to be oxidized to alcohols, but alkyl side chains of aromatic compounds are more readily oxidized, often at more than one position, and so provide good examples of this type of oxidation. The n-propyl side chain of n-propyl benzene can be oxidized at any one of three carbons to yield 3-phenylpropan-l-ol (C6H5CH2CH2CH2OH) by -oxidation, benzylmethyl carbinol (C6H5CH2CHOHCH3) by co-1 oxidation, and ethyl-phenylcarbinol (C6H5CHOHCH2CH3) by -oxidation. Further oxidation of these alcohols is also possible. 

IOB alone can oxidize some alcohols, but catalysed oxidations are much more efficient. Thus, in the presence of RuCl2(PPh3)2 primary aliphatic alcohols were oxidized cleanly to aldehydes, at room temperature the use of m-iodosylbenzoic acid instead of IOB considerably increased the yields for example, hexanal was formed from hexanol quantitatively (by GC) [19], Another catalytic system involved the use of simple lanthanide salts such as ytterbium triacetate [20]. Cyclic y-stannyl alcohols, readily available from cyclic vinyl ketones and Bu3SnLi, underwent oxidation accompanied by carbon-carbon bond cleavage (Grab fragmentation), when treated with IOB.BF3 and DCC. The products were unsaturated aldehydes or ketones. 

Pentacarbonyl(methoxymethylcarbene)tungsten(0) is a dull-yellow, crystalline solid mp 52°. It is appreciably more stable thermally and oxidatively than its chromium analog in the solid state at room temperature and may be stored at 5° for a period of 1 or 2 weeks without significant decomposition. It is soluble in aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, and other common laboratory solvents such as benzene, 1,4-dioxane, tetrahydrofuran, chloroform, dichloromethane, and methanol it is slightly soluble in ethanol. The infrared spectrum (cyclohexane solution) has v(CO) bands at 2075, 1980, 1960, and 1947 cm"1. The nmr spectrum in chloroform-d has the methoxy proton resonance at t6.17 and the methyl proton resonance at t7.69. Other physical properties are reported in the literature.6,7... 

Ti, V and Sn-modified mesoporous silicates were reported to be active in a number of liquid phase oxidation reactions. Ti-containing samples were used for the selective oxidation of large organic molecules in the presence of te/t-butyl hydroperoxide (TBHP) or dilute H2O2 [71,136,137,139-141,147,186,237]. Typical data shown in Table 5 indicate that both Ti-MCM-41 and Ti-HMS are efficient cat ysts for the epoxidation of bulky olefins such as a-terpineol and norbomene in the presence of TBHP or H2O2. Comparison with H-B indicates that the accessibility of active sites plays a critical role in the liquid phase oxidation of organic molecules. Mesoporous titanosilicates also exhibited remarkable activity in the hydroxylation of 2,6-di-rerr-butyl phenol (2,6 DTBP) [142,147] and the oxidation of cyclododecanol [147], naphthol [147] aniline [237] and chloroaniline [186]. However, they were disappointingly poor catalysts for the liquid phase oxidation of n-hexane and aliphatic primary amines, as well as the ammoximation of cyclohexanone [147,238]. 

Carbon dioxide, water, ethane, ethylene, propane, ammonia, xenon, nitrous oxide, and fluoroform have been considered useful solvents for SEE. Carbon dioxide has so far been the most widely used as a supercritical solvent because of its convenient critical temperature, 304°K, low cost, chemical stability, nonflammability, and nontoxicity. Its polar character as a solvent is intermediate between a truly nonpolar solvent such as hexane and a weakly polar solvent. Moreover, COj also has a large molecular quadrupole. Therefore, it has some limited affinity with polar solutes. To improve its affinity, additional species are often introduced into the solvent as modifiers. For instance, methanol increases C02 s polarity, aliphatic hydrocarbons decrease it, toluene imparts aromaticity, R-2-butanol adds chirality, and tributyl phosphate enhances the solvation of metal complexes. 

Aliphatic EC5-EC8 Fraction. Examination of urinary metabolites in humans and rats after exposure to /7-hexane indicates that hydrocarbons in this fraction may be oxidatively metabolized via cytochrome P-450 oxidases to several alcohol, ketone, and carboxylic acid derivatives. Based on... 

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