Alkanes oxyfunctionalization

The oxyfunctionalization of alkanes with H2O2 on TS-1 has only been reported very recently [113-114]. Linear or branched alkanes are oxidized to secondary and/or tertiary alcohols and ketones, the latter ones being formed by consecutive oxidation of the secondary alcohols. Primary alcohols are not detected. At 50°C maximum turn-overs of n-hexane of 35 mol/mol Ti were reported... 

In 1992, Hari Prasad Rao and Ramaswamy reported on the oxyfunctionalization of alkanes with H2O2 using a vanadium silicate molecular sieve s . With this catalyst acyclic and cyclic alkanes were oxidized to a mixture of the corresponding alcohols (primary and secondary ones), aldehydes and ketones. Unfortunately, most of the early attempts were of rather limited success due to low turnover frequencies and radical producing side reactions as observed, for example, by Mansuy and coworkers in 1988. ... 

Direct insertion into an X—H a bond constitutes the highlight of dioxirane chemistry . Besides the insertion of a dioxirane oxygen atom into an alkane acH bond, for practical purposes a most valuable oxyfunctionalization, also the more facile insertion into the asiH bond is known, a convenient and chemoselective method of preparing silanols. 

For the oxidation of alkanes, the reactivity order follows the sequence primary < secondary < tertiary < benzylic < allylic C—H bonds. The readily accessible and economical DMD is suitable for most substrates, although this oxyfunctionalization may... 

The oxidation of organic substances by cyclic peroxides has been intensively studied over the last decades , from both the synthetic and mechanistic points of view. The earliest mechanistic studies have been carried out with cyclic peroxides such as phthaloyl peroxide , and more recently with a-methylene S-peroxy lactones and 1,2-dioxetanes . During the last 20 years, the dioxiranes (remarkable three-membered-ring cyclic peroxides) have acquired invaluable importance as powerful and mild oxidants, especially the epoxidation of electron-rich as well as electron-poor alkenes, heteroatom oxidation and CH insertions into alkanes (cf. the chapter by Adam and Zhao in this volume). The broad scope and general applicability of dioxiranes has rendered them as indispensable oxidizing agents in synthetic chemistry this is amply manifested by their intensive use, most prominently in the oxyfunctionalization of olefinic substrates. 

IRON-PHTHALLOCYANINES ENCAGED IN ZEOLITE Y AND VPI-5 MOLECULAR SIEVE AS CATALYSTS FOR THE OXYFUNCTIONALIZATION OF n-ALKANES... 

In the present work, the construction of a mimic of cytochrome P-450 is attempted by in situ synthesis of iron-phthallocyanines in the supercages of zeolite Y and in the channels of VPI-5. Its catalytic activity and selectivity is tested in the oxyfunctionalization of n-alkanes with tertiary butyl hydroperoxide. 

Oxyfunctionalization reactions of n-alkanes are carried out at room temperature and atmospheric pressure with t.BHP as oxidans and acetone as solvent. Product analysis was done with GC on a 50 m CP Sil-88 capillary column from Chrompack. 

A new approach to the oxyfunctionalization of alkanes with isolated dioxiranes has been reviewed. Dioxiranes achieve oxidation of alkanes with high selectivity for both... 

The C-H oxidation of unactivated alkanes is the most direct method of introducing oxygen functional groups in alkanes. Such oxyfunctionalization, especially... 

Figure 1. Classification of oxidoreductases with a focus on enzymes capable of sp3-carbon oxyfunctionalization. MMO, methane monooxygenase AMO, alkane monooxygenase XMO, xylene monooxygenase. The most prominent enzyme classes in respect of sp3-carbon oxyfunctionalization are shown in bold.

The oxyfunctionalization of low molecular weight alkanes has attracted much attention because of their low cost and chemical stability as feedstock. Their oxidation over POM catalysts has been widely studied by controlling redox properties upon substituting M addenda by transition metal elements [61-63]. For example. 

The discovery in the early 80 s of titanium silicalites [62-64] opened the new application perspective of zeolitic materials as oxidation catalysts. Several reactions of partial oxidation of organic reactants using dilute solutions of hydrogen peroxide could for the first time be performed selectively in very mild conditions. Other elements inserted in the lattice of silicalites have since been shown to have similarly interesting catalytic properties including, vanadium, zirconium, chromium and more recently tin and arsenic [65]. Titanium silicalites with both MFI (TS-1) and MEL (TS-2) structures have however been the object of more attention and they still seem to display unmatched properties. Indeed some of these reactions like the oxyfunctionalization of alkanes [66-69] by H2O2 are not activated by other Ti containing catalysts (with the exception of Ti-Al-Beta [70]). The same situation... 

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... 

The unusual reactivity of dioxiranes is impressively exhibited in their ability to insert into C — H bonds (Scheme 7) [28]. Thus, tertiary alkanes are oxidized to their respective alcohols [29]. In the example shown, the insertion took place with complete retention of configuration at the chirality center. 1,3-Dicarbonyl derivatives [30] are hydroxylated with high efficiency, but more than likely the intermediary enol is being oxyfunctionalized. Secondary alcohols are transformed into ketones, a specific example is the oxidation of the epoxy alcohol in the rosette [31], In an attempt to epoxidize the hydroxy acrylic ester [22], the epoxy 1,3-dicarbonyl product was obtained, although in low yield in accord with its rather reluctant nature towards oxidation. 

Direct Functionalization of C-H Bonds by Dimethyl-dioxirane. The efficient oxyfunctionalization of simple, unactivated C-H bonds of alkanes under extremely mild conditions undoubtedly is one of the major highlights of dioxirane chemistry. ... 

In a related approach, nonactivated terminal carbons were directly aminated by using a recombinant whole-cell catalyst [33]. In the key steps, an oxygenase and an m-TA were coupled in vivo within a single Escherichia coU host (BL21) (Scheme 4.8). For the oxidation of the alcohol to the respective aldehyde, the NADH-dependent oxygenase AUcBGT from Pseudomonas putida was used, which allowed the oxyfunctionalization of medium-chain-length alkanes, fatty acids [34], and selected fatty acid methyl esters [35]. Subsequent reductive amination was achieved... 

---