Ethane from oxidation

The Wacker Oxidation is an industrial process, which allows the synthesis of ethanal from ethene by palladium-catalyzed oxidation with oxygen. Copper serves as redox cocatalyst. 

Flego [1] recommends the use of micro devices for automated measurement and microanalysis of high-throughput in situ characterization of catalyst properties. Murphy et al. [5] stress the importance of the development of new reactor designs. Micro reactors at Dow were described for rapid serial screening of polyolefin catalysts. De Bellefon ete al. used a similar approach in combination with a micro mixer [6], Bergh et al. [7] presented a micro fluidic 256-fold flow reactor manufactured from a silicon wafer for the ethane partial oxidation and propane ammoxidation. 

The reductive elimination of ethane from [Cp Rh(PPh3)Me2] was found to be increased by a factor of at least 3 x 109 upon oxidation to the 17-electron radical cation.157 The absence of solvent effects on the rate was interpretated to indicate direct elimination from the cation to give ethane and a 15-electron intermediate, which is rapidly trapped by solvent. 

Methane-based commercial production of ethylene via oxidative coupling has been investigated, but to date the lower per pass conversions required for acceptable ethylene selectivities combined with purified oxygen costs make this process noncompetitive with thermal cracking of ethane from natural gas liquids. 

Alkanes, e.g., pentane, produced by this mechanism as an end-product of the oxidation of linoleic and arachidonic acid, and ethane from linolenic acid (Fig. 2.13) (Tappel and Dillard, 1981). 

Fig. 15. The influence of the pic d arret on product forrhation during the oxidation of propane. Initial temperature = 430 °C initial pressure of propane = 90 torr initial pressure of oxygen = 210 torr volume of reaction vessel = 30 cm , (b) Left ordinate +, methyl alcohol. Right ordinate x, isopropyl alcohol , ethyl alcohol o, n-propyl alcohol 1, allyl alcohol, (c) Left ordinate +, hydrogen peroxide , formaldehyde. Right ordinate x, total aldehydes, (d) +, propene i, methane , ethylene x ethane. (From ref. 147.)...

However, if in nonaqueous solutions (discussed next) the oxidations also proceed through oxypalladation adducts, then the two mechanisms of decomposition of the oxypalladation adducts would predict diflFerent products. First, let us consider the mechanism of Jira, Sedlmeier, and Smidt (Reactions 50-53). In this case OH in II (Reaction 52) is replaced by OR. Decomposition via Reaction 55 is impossible, so II must decompose by solvolysis. This would give 1,1-disubstituted ethanes from ethylene oxidation. On the other hand, the first suggestion (Reaction 48) would probably be more consistent with formation of the vinyl compounds since hydride elimination should be completed if a rapid rearrangement of electrons to give acetaldehyde cannot occur. Evidence exists that 1,1-disubstituted ethanes are the initial products in methanol, and in acetic acid it is claimed that both vinyl acetate and 1,1-diace-toxyethane are initial products this suggests that in this solvent competition exists between palladium (II) hydride elimination and acetate attack. However, until now there have been no detailed studies of the oxidation under conditions where 1,1-disubstituted products are formed. More work is needed before the course of the reaction under these conditions is completely understood. 

The spectroscopic probe pyridine-N-oxide was used to characterize polar microdomains in reverse micelles in supercritical ethane from 50 to 300 bar. For both anionic and nonionic surfactants, the polarities of these microdomains were adjusted continuously over a wide range using modest pressure changes. The solubilization of water in the micelles increases significantly with the addition of the cosolvent octane or the co-surfactant octanol. Quantitative solubilities are reported for the first time for hydrophiles in reverse micelles in supercritical fluids. The amino acid tryptophan has been solubilized in ethane at the 0.1 wt.% level with the use of an anionic surfactant, sodium di-2-ethylhexyl sulfosuccinate (AOT). The existence of polar microdomains in aggregates in supercritical fluids at relatively low pressures, along with the adjustability of these domains with pressure, presents new possibilities for separation and reaction processes involving hydrophilic substances. 

Materiala. Nonionic surfactants Brij 52 (B52) and Brij 30 (B30) were obtained from the Sigma Chemical Company and used as received. These surfactants are ethoxylated alcohols with the nominal structures Cie a and C12E4, respectively, where E represents the number of ethylene oxide units. Acrylamide was obtained from the Aldrich Chemical Company (Gold Label 99-1-%) and recrystallized twice from chloroform. Azo bis(isobutyrnitrile) (AIBN), obtained from the Alfa Products Division of Morton Thiokol, was recrystallized from methanol. Water was doubly deionized. Propane obtained from Union Carbide Linde Division (CP Grade) and ethane from Air Products (CP Grade) were used without further purification. 

Recently, Sen has reported two catalytic systems, one heterogeneous and the other homogeneous, which simultaneously activate dioxygen and alkane C-H bonds, resulting in direct oxidations of alkanes. In the first system, metallic palladium was found to catalyze the oxidation of methane and ethane by dioxygen in aqueous medium at 70-110 °C in the presence of carbon monoxide [40]. In aqueous medium, formic acid was the observed oxidation product from methane while acetic acid, together with some formic acid, was formed from ethane [40 a]. No alkane oxidation was observed in the absence of added carbon monoxide. The essential role of carbon monoxide in achieving difficult alkane oxidation was shown by a competition experiment between ethane and ethanol, both in the presence and absence of carbon monoxide. In the absence of added carbon monoxide, only ethanol was oxidized. When carbon monoxide was added, almost half of the products were derived from ethane. Thus, the more inert ethane was oxidized only in the presence of added carbon monoxide. 

Recently we observed the effect which supports the conclusion about the substantial role of the radical reaction outside of the catalyst grains. When a very efficient OCM oxide catalyst (10% Nd/MgO) was placed into the reactor together with an inactive metal filament (Ni-based alloy) the sharp increase of conversion accompanied by the selectivity shift from oxidative coupling to the formation of CO and H2 was observed [19]. Since the metal component has a low activity also with respect to ethane oxidation, this behavior is not due to successive oxidation or decomposition of C2 hydrocarbons on the metal surface, but should be attributed to the reactions of methane oxidation intermediates. Almost total disappearance of ethane (which is a product of CH3 radicals recombination) and acceleration of the apparent reaction rate by the addition of an "inert material indicate that the efficiency of methane oxidative transformations can be substantially increased if the radicals have a chance to react outside the zone where they formed and the role of reaction (-1) decreases. Although the second (metal) surface is not active enough to conduct the reaction of saturated hydrocarbon molecules (methane and ethane), the radicals generated by the oxide can react further on the metal surface. As a result, the fraction of the products formed from methane activated in the reaction (1) increases, and the formation of the final reaction mixture of different composition takes place. 

As is the case with methane, experiments have been performed with ethane for the purpose of separation of gaseous mixtures in analytical procedures. Phillips37 found that ethane was oxidized in a 3.1 per cent mixture with air at 450° C. over palladium asbestos. Mixtures of ethane and methane are difficult to separate by preferential combustion over platinum or palladium but hydrogen may be removed from such mixtures due to its lower reaction temperature.31 The nature of the products obtained from the hydrocarbon oxidation in these experiments was not reported. 

In continuing this work Drugman 145 used air containing 10 per cent of ozone and found that although ethane was oxidized but slowly at 15° C the reaction was more rapid than with methane. At 100° C. with a large excess of ethane much less acetic acid was formed but more ethanol was recovered from the wash traps. In each instance acetaldehyde was the main reaction product. Drugman concluded from these results that... 

Oxidation of [Rh °(Cp )Me2(dmso)] in DMSO (dimethyl sulfoxide) also resulted in reductive elimination of ethane from the le oxidized species... 

Figure 33. Oxidatively induced reductive elimination of ethane from [Rh (Cp )Me2(L)] species followed by a comproportionation reaction between [Rh (Cp )Me2(L)] and [Rh (Cp )(solv)(L)] to form [Rh(Cp )Me(L)(solv)].

Puddephatt etal. [41] have studied the C-H or C-C bond activation in the alkane complexes [PtMe(CH4)L2] or [PtMe(CHjCH3)L2] (L = NH3 or PH3) as well as the reductive elimination of methane or ethane from the five-coordinate model complexes [PtHMe2L2] or [PtMesLi], respectively, by carrying out extended Hiickel molecular orbital calculations and density functional theory. The oxidative addition and reductive elimination reactions occur by a concerted mechanism, probably with a pinched trigonal-bipyramidal complex on the... 

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