Neopentane oxidation

Petway, S. V. Application of Automatic Reaction Model Generation to Chlorine-Initiated Neopentane Oxidation, (Poster Presentation) 6th International Conference on Chemical Kinetics, NIST (Gaithersburg, MD) (2005). 

A subsequent study using neopentane as the alkane substrate gave evidence in support of the same mechanism, and also allowed resolution of near-coincident y(CO) absorptions due to [Cp Rh(CO)Kr] (1946 cm ) and [Cp Rh(CO)(di2-neopen-tane)] (1947 cm ) [18]. Further studies were able to quantify the reactivity of [Cp Rh(CO)Kr] towards a range of alkanes [20]. It was found that binding of the alkane to Rh becomes more favorable, thermodynamically, as the alkane size is increased, but that the rate of the C-H oxidative addition step shows less variation with linear alkane chain length. No reaction with methane was observed, which was explained by the ineffective binding of methane (relative to excess Kr) to Rh. 

Table I. Effect of Surface on Initial Product Distribution in the Oxidation of Neopentane...

The production of O( )) atoms is also evidenced by the formation of neopentanol in the photolysis of N20-neopentane mixtures at 2138 A. On the other hand, Of3P) atoms react with 1-butene to yield 1,2-butene oxide [Paraskevopoulos and Cvetanovic (791)]. 

In particular cases bond strengths may be controlling—for example, the extreme resistance of benzene to oxidative attack may be explained by the very high C—H bond strength (12, 208). The anomalous low knock rating of neopentane may be correlated with the low strength of the neopentyl C—H bond. C—H bond strengths for methane, ethane, and neopentane are, respectively, 102, 98, and 96 kcal. per mole (82, 204). 

Considering the various alkanes shown below, one sees that alkanes can have several different oxidation levels for carbon. Oxidation levels can range from —4 for methane and —3 for the carbon atom of methyl groups all the way to 0 for the quaternary carbon of neopentane. In spite of the several oxidation levels possible in alkanes, the functional group approach tells us that all are saturated alkanes and thus have the same functional equivalency and similar reactivity patterns. 

The same process can be carried out to determine the oxidation levels of carbon atoms in several common functional types. It is clear that by using these procedures we can assign oxidation levels to carbon atoms in a wide variety of compounds. It is also clear that knowing the oxidation level is insufficient to assign the functional group present. For example, the alkane neopentane, the alkene isobutylene, the alkyne propyne, the alcohol isopropanol, and formaldehyde all have a carbon with an oxidation level of 0 yet all belong to completely different functional classes and have different physical and chemical characteristics. 

More recently, the reactivity of SZ has been assigned to its oxidizing ability,129-131 which should not be surprising because it has often been considered as SO3 adsorbed on zirconium oxide. However, that sulfated zirconia is not only an oxidant but also a strong protic acid has been demonstrated by Sommer, Walspurger, and co-workers132 on the basis H/D exchange experiments with neopentane. 

Catalytic superactivity of electron-deficient Pd for neopentane conversion was recently verified for Pd/NaHY (157, 170). The reaction rate was positively correlated with the proton content of the catalyst. Samples that contained all the protons generated during H2 reduction of the catalysts were two orders of magnitude more active than silica-supported Pd. Samples prepared by reduction of Pd(NH3)2+NaY displayed on intermediate activity. It was suggested that Pd-proton adducts are highly active sites in neopentane conversion. With methylcyclopentane as a catalytic probe, all Pd/NaY samples deactivated rapidly and coke was deposited. Two types of coke were found (by temperature-programmed oxidation), one of... 

Hoyano JK, Graham WAG. Oxidative addition of the carbon-hydrogen bonds of neopentane and cyclohexane to a photochemically generated iridium(I) complex. J Am Chem Soc 1982 104(13) 3723-3725. 

J. K. Hoyano, and W. A. G. Graham, Oxidative Addition of the Carbon-Hydrogen Bonds of Neopentane and Cyclohexane to a Photochemically Generated Iridium(I) Complex, J. Am. Chem. Soc. 104, 3723-3725 (1982). 

The electron donicity of alkylmetal complexes is strongly enhanced when a negative charge is introduced. Thus, polyalkylmetallates such as borates or aurates exhibit oxidation (peak) potentials much lower than neutral polyalkylmetal complexes (compare Tables 1 and 5). An extreme case represents dimethylaurate(I) with an oxidation (peak) potential of 0.1 V (relative to the SCE) [64] which is more than 1 V lower than that of the isoelectronic dimethylmercury(II) complex (Eqx = 1 46 V relative to the SCE) [42]. Similarly, the oxidation potential of tetramethylborate (Eotl = 0.58 V relative to the SCE) [65] is substantially lower than that of the isoelectronic neopentane which exceeds 3 V [66]. 

Hydrolysis of A under very mild conditions (p(H20) = 22 torr, 25°C) leads to the formation of surface zirconium hydroxides, 2, with evolution of 3 mol neopentane/Zr. It is very difficult to prove unambiguously that the Zr sites remain isolated on the surface, but the absence of an absorption band in the UV spectrum and the catalytic activity of these solids (see below) stron y suggest that no large ZrO particles have formed. Hydroxycomplexes of Zr (or Ti) are presumed intermediates in the mild oxidation reactions performed with H2O2. 

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