Alkanes cobalt acetate oxidation

These types of process are frequently encountered and imply electron transfer from the C H bond to the metal with the formation of radical cations. The Co(IU) acetate oxidation of alkanes probably proceeds, however, through the formation of a radical cobalt complex [S3]. 

In the presence of strong acid activators, such as TFA, cobalt(III) acetate is capable of the selective oxidation of alkanes under mild conditions to alkyl acetates, ketones, or alkyl chlorides, depending on the reagents used.298 For example, the oxidation of n-heptane carried out at 25°C, is illustrated in the following examples ... 

The use of mixed-metal catalysts can also dramatically affect the products of autoxidations. An example mentioned earlier is the selective oxidation of acetaldehyde to acetic anhydride in the presence of a mixture of cobalt and copper acetates. Another example is the co-oxidation of alkanes and olefins in the presence of both an autoxidation and an epoxidation catalyst (see Section III.B) ... 

In the past, acetic acid was produced by aerobic oxidation of n-butane (and also of light naphtha, which is mainly a mixture of liquid -alkanes up to C9H2o). The process catalyzed by cobalt(II) acetate, closely resembled the one-step... 

Oxidation of n-butane. In the presence of oxygen, Co(l 1) is converted into Co(lll), the actual catalyst for oxidation of alkanes by oxygen thus oxidation of n-butane by Co(lll) ion at 100° at a pressure of 17-24 atm. gives acetic acid (83.5% yield) together with traces of n-butyric acid, propionic acid, and methyl ethyl ketone. Oxidation of n-pentane under similar conditions gives acetic acid (48% yield) and propionic acid (27% yield). Isobutane is relatively inactive. The reaction involves electron transfer in which cobalt ions function as chain carriers. 

Because oxidations with oxygen are free-radical reactions, free radicals should be good initiators. Indeed, in the presence of hydrogen bromide at high enough temperatures, lower molecular weight alkanes are oxidized to alcohols, ketones, or acids [5 7]. Much more practical are oxidations catalyzed by transition metals, such as platinum [5, 6, 55, 56], or, more often, metal oxides and salts, especially salts soluble in organic solvents (acetates, acetylacetonates, etc.). The favored catalysts are vanadium pent-oxide [3] and chlorides or acetates of copper [2, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66], iron [67], cobalt [68, 69], palladium [60, 70], rhodium [10], iridium [10], and platinum [5, 6, 56, 57]. 

Oxidation of n-alkanes by Co acetate in acetic acid occurs with a remarkable regioselectivity (rs) at the alkyl acetate as the major product in anaerobic conditions, and 2-alkanone in the presence of oxygen (equations 233 and 234). Cyclohexane is readily oxidized in nitrogen by Co(OAc)3 in acetic acid to mainly cyclohexyl acetate and 2-acetoxycyclo-hexanone. In the presence of oxygen and a high cobalt concentration, adipic acid is the major product formed (equation 235). Oxidation of adamantane by Co(OAc)s and TFA in AcOH preferentially occurs at the tertiary positions, producing 1-adamantyl acetate as the major product. ... 

Most of the catalysts employed in the chemical technologies are heterogeneous. The chemical reaction takes place on surfaces, and the reactants are introduced as gases or liquids. Homogeneous catalysts, which are frequently metalloorganic molecules or clusters of molecules, also find wide and important applications in the chemical technologies [24]. Some of the important homogeneously catalyzed processes are listed in Table 7.44. Carbonylation, which involves the addition of CO and H2 to a C olefin to produce a + 1 acid, aldehyde, or alcohol, uses rhodium and cobalt complexes. Cobalt, copper, and palladium ions are used for the oxidation of ethylene to acetaldehyde and to acetic acid. Cobalt(II) acetate is used mostly for alkane oxidation to acids, especially butane. The air oxidation of cyclohexane to cyclohexanone and cyclohexanol is also carried out mostly with cobalt salts. Further oxidation to adipic acid uses copper(II) and vanadium(V) salts as catalysts. The... 

Cobalt compounds are among the most efficient catalysts of alkane and aryl alkane autoxidation [16], Toluene oxidation by dioxygen at 60 °C in acetic acid in the presence of Co(III) at the initial stages gives exclusively benzaldehyde [16d]. The reaction proceeds without an induction period, reaching the maximum rate at the begiiming of the reaction. The kinetic equation for the oxidation is... 

Direct oxidation, similarly to the first step of cyclohexane oxidation above, is a useful reaction for selective oxidation of simple alkanes relatively high concentrations of cobalt(II) acetate are... 

The relative rates of oxidation of various cycloalkanes by cobalt(III) acetate in acetic acid have been reported [36-38]. The complex formation between the alkane and Co(III) is strongly influenced by steric factors. 

Strong acids like e.g. trifluoroacetic acid (TFA) accelerate alkane oxidation (similarly to arene oxidation), as illustrated by the oxidation of n-heptane to 2-heptyl acetate by cobalt(III) in acetic acid-TFA mixture, or to 2-heptanone under dioxygen [40]. 

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