Oxidation hexane

The composition of an oxidizing mixture is altered extensively by the passage of a cool flame (66,83,84). Before passage of the flame, oxygenated materials are present. In the case of hexane oxidation, ROO radicals are reportedly displaced by HOO radicals above 563 K (85), in concordance with previous work (86,87). After the passage of a cool flame, olefins, some conjugate and others of lower molecular weight, are observed. 

The products of the oxidation reaction were analysed by gas chromatography (Hewlett Packard, 5880 A), employing a FID detector and equipped with a capillary column (50 m x 0.25 mm crosslinked methyl silicone gum). The reactants and products of n-hexane oxidation were analysed by gas chromatography (Hewlett Packard, 5890) equipped with a FFAP column (30 m X 0.25 mm). The identity of the products was further confined by GC-MS (Shimadzu QCMC-QP 2000A). 

In the linear versus cyclic case, n-hexane oxidizes 18.9 times as fast as cyclohexane (see Fig. 6-6) however, under slightly different conditions (same temperature and pressure, acetone solvent) and a slightly different preparation of TS-1, n-hexane oxidizes only 4.8 times as fast as cyclohexane.45 These differences in TOFs between the linear and cyclic isomers are also attributed to the size restrictions of the zeolite. When the channel diameter is increased, as in the Ti-(1 catalyst (-6.5 A), larger cycloalkanes, such as cyclododecane, can be oxidized.45... 

FIGURE 6.7 Effect of methanol on TON of n-hexane oxidation by H202 over TS-1.51... 

The treatment leads to a significant improvement in alkene conversion in cyclohexene epoxidation in the case of Ti-MCM-41 and Ti-MCM-48 (273). Although epoxide selectivity improved in the former case, there was a decrease in the latter. In the case of hexane oxidation, silylation did not improve the conversion. An enhancement in the number of turnovers and selectivity for the epoxide on silylation was also observed in the cyclohexene epoxidation with TBHP catalyzed by Ti-SBA-15 (Table LII) (274). Ti-SBA-15 was claimed to be thermally more stable than Ti-MCM-41. Ti leaching was absent. 

B. Methylenecy do hexane oxide. I he Gooch tubing is removed... 

Szabo, V Bassir, M Gallot, JE van Neste, A Kaliaguine, S. Perovskite-type oxides synthesized by reactive grinding Part III. Kinetics of n-hexane oxidation over LaCoi. xFcxOs. Appl. catal, B Environmental, 2003, Volume 42, Issue 3, 265-277. 

Moderate amounts of formaldehyde exerted an inhibiting effect by increasing the induction period in pentane and hexane oxidation (13). The higher aldehydes and formaldehyde appear in approximately equivalent amounts. Decomposition of alkoxy radicals, RCH20 —> R + CH20, is considered the source of formaldehyde. The effect of added formaldehyde is shown in Table I. 

Mn and Fe chemistry has shown that zeolites are excellent supports for anchoring of metallophthalocyanines. There is a report of n-hexane oxidation with O2 and zeolite-supported Cu-perchlorophthalocyanine catalyst (189) ... 

Hexanal oxidation To hexanoic acid. Decrease in hexanal monitored by GC Yanagimoto et al.45i... 

The reducing equivalents released from aerobically consumed fuels are transferred to oxygen, producing water, Including water in the formula for hexane oxidation yields... 

Sodium permanganate, which is used as its monohydrate in solid form in refluxing dichloromethane or hexane, oxidizes allylic alcohols more slowly and in lower yields than the saturated alcohols. 2-Cyclohexen-l-ol, after a 24-h reflux in hexane, furnishes a 47% yield of the ketone, whereas cyclohexanol gives a 100% yield after 1.5 h [555]. 

The oxyfunctionalization of linear alkanes at the terminal position is one of the major challenges of catalysis in the case of n-hexane, oxidation at the two terminal C atoms would lead to AA. However, there is a little amount of n-hexane in cracker streams, because it is easily converted to benzene. Therefore, sourcing of this hydrocarbon would be a challenge. 

With microporous Co(III)- and Mn(III)-aluminophosphates, MnAPO-18 and CoAPO-18, unprecedented terminal selectivities have been reported in w-hexane oxidation with oxygen on structures with small eight-ring windows (0.38 nm) [43l-pj. This created a ready access to the Co site by the terminal group of the linear alkane, with the alkane gaining entry into the interior of the porous catalyst with an end-on approach, thus limiting the oxyfunctionalization at the other C atoms. With both... 

Despite the relevance of these findings and the implications that they may have [43q, r] these excellent figures were not confirmed using catalysts with an identical composition and structure, namely, MnAPO-5 and MnAPO-18 [43s, t]. It was reported that n-hexane oxidation turnover rates (per redox-active Mn center) by oxygen were similar on MnAPO-5 and MnAPO-18, because the reactant may rapidly diffuse and reach the active site, regardless of the pore size in the microporous structure. No regiospedficity was detected for w-hexane oxidation to alkanols, aldehydes and ketones (7-8% terminal selectivity), and the relative reactivity of primary and secondary C—H bonds in w-hexane was identical in both catalysts and similar to that predicted from relative C—H bond energies in n-hexane. The selectivity to terminal adds was very low. 

The carbon monoxide and hexane oxidation activities of class I spinels were measured (Table II). Activity and activity loss were related to catalyst surface area and stability respectively. DSC data for class II spinels are not tabulated these spinels were all essentially inactive with 50% exotherm temperatures being greater than 375°C. 

The oxidation activity increases with distance from the reactor inlet, as expected. Arrehenius plots for hexane oxidation data are shown in Figure 6. 

Figure 6 Arrehenius plots for hexane oxidation data...

Another approach to the simulation of the catalyst s microenvironment is its immobilization on a solid support, i.e., the formation of heterogeneous oxygenase systems. Immobilization of a metalloporphyrin on porous glass [80] or polyvinylpyrrolidone [81] markedly increases the selectivity of alcohol formation. Immobilization of an iron-porphyrin complex on zeolites [82], Si02 [83] and especially on graphite, strongly increases the steric effects, which are observed in hexane oxidation in model systems with active oxygen species [84]. The effect of the matrix is not confined to the increase in the steric hindrances around the active oxidant. It can also be accompanied by a sieve effect, which is well-known for zeolites and accounts for the differences in the substrate specificity. 

Nakayama et at. used thienyl-substituted 1,4-dithiins which are obtained from easily accessible diketosulfides for the preparation of a-oligothiophenes and isomers up to the heptamer [37b, 120]. The dithienyldiketosulfides 91-93 are prepared by the reaction of chloroaeetyl-substituted (oligo)thiophenes and sodium sulfide in almost quantitative yield and are further cyclized to the corresponding 1,4-dithiins 94-96 with L.R. in 60% yield. The extrusion of sulfur from the dithiin moiety via ylide intermediates is achieved by refluxing the dithiin in o-dichlorobenzene and results in a mixture of two possible isomers [Eq. (45)]. In the case of 2,6-di-(2 thienyl)-1,4-dithiin 94, a ratio of 13 1 of H-T3-H 3 and the 2,3 4, 2"-isomer 97 in 85% yield is obtained. The separation of the compounds by recrystallization turns out well since the a,/ -connected terthiophene is better soluble in hexane. Oxidation of the dithiin with nz-chloroperoxybenzoic add and extrusion of SO from the resulting sulfoxide in the presence of DMSO afford a mixture of H-T3-H 3 and the isomer 97 in a ratio of 22 1 and in a total yield of 90% [120]. 

Inverse gas chromatography parameters can also be applied in the field of cafaly-sis. In fhis way, as example, parent NaX and CaA zeolites, as well as transition metal (Co +, Mn +, Fe " )-exchanged zeolites, were evaluated for the catalytic oxidation of n-hexane. It was observed [51, 52], that although there was linear correlation between the acidity and the adsorption enthalpy of the n-hexane, there was no relationship between the acidity and the activity for n-hexane oxidation. However, if a reactivity parameter (such as Tso, temperature at which 50 % of conversion is attained) is plotted versus the adsorption heat, a so-called Volcano plot is obtained (Fig. 16.12), an optimum value of (-AH ) being observed, higher and lower values yielding to worst catalytic performance. 

Mesoporous Cu0-Fc203 composite catalysts for complete f-hexane oxidation... 

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