Alkanes, thermal oxidations

General Scheme for Chain Propagation. The reactions which have been discussed may be combined into a system of chain propagation which should be a general one during the thermal oxidation of alkanes. 

Once initiated, photooxidation may proceed through a free-radical chain mechanism analogous to that commonly used to explain the thermal oxidation of alkanes in the liquid phase. 

The most recent catalysts that operate under thermal conditions were then based on the premise that a Cp M fragment with ligands that dissociate under thermal conditions could be a catalyst for alkane borylation. After a brief study of Cp IrH4 and Cp Ir(ethylene)2, Dr. Chen studied related rhodium complexes. Ultimately, he proposed that the Cp Rh(ri" -C6Me6) complex would dissociate CeMce as an iimocent side product, and that Cp Rh(Bpin)2 from oxidative addition of pinBBpin (pin=pinacolate) would be the active catalyst. The overall catalytic... 

The transfer reaction utilizes a sacrificial alkene to remove the dihydrogen from the pincer or anthraphos complex first, before the oxidative addition of the target alkane. The elementary reaction steps are slightly different from the thermal reaction, which is discussed in the next section, both in their order and their direction. For simplicity, we describe the symmetric reaction where the sacrificial alkene is ethylene and the reactant is ethane (21b). The elementary reaction steps for the mechanism of this transfer reaction involve IVR, IIIR, VIR, VI, III and IV, where the superscript R stands for the reverse of the elementary steps listed in Section III. These reverse steps (IVR, IIIR, and VIR) involve the sacrificial alkene extracting dihydride from the metal to create the Ir(I) species 8, while steps VI, III and IV involve oxidative addition of target alkane, p-H transfer and olefin loss. 

Thermal decomposition of oxetanes proceeds at elevated temperatures, usually in the range of 300-450 °C, to give an alkene and a carbonyl compound in practically quantitative yield. Gas phase thermolyses of several alkyl-substituted oxetanes have been studied in detail, because such compounds occur as intermediates in the oxidation of alkanes (Section 5.13.3.3). When the oxetane is unsymmetrically substituted, as in the case of 2,4-dimethyl-oxetane (20), two modes of cleavage, to give two different sets of products, are possible and are generally observed. In fact, when only hydrogen and alkyl substituents are present,... 

Perfluoroalkanes (i.e., alkanes in which all H atoms are replaced by F) have high thermal stability and resistance to oxidation and hydrolysis. This is... 

Substrates which can undergo partial oxidation are characterized by a 7T-electron system or unshared electrons olefins and aromatics contain the first, methanol, ammonia and sulphur dioxide the second. Alkanes do not contain such electrons. Their selective oxidation appears to demand (thermal or catalytic) dehydrogenation to alkenes as the initial process. 

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