Butane autoxidation

An azeotrope is a liquid mixture that has the same composition both in the liquid and in the vapor phase. This means that the components cannot be separated by conventional distillation. In such cases an entrainer or a third component is added to make the compositions of the liquid and the gas phases different. In the case of liquid-phase butane autoxidation (Section 8.4), 2-bu-tanone is separated as a pure component by adding entrainment agents such as ether to break the azeotrope the ketone forms with water. 

Butane oxidation in the presence of cobalt(III) acetate in acetic acid occurs at temperatures of 100-125 °C. Acetic acid is the reaction product with 83% selectivity (at 80% conversion) [Ij, 17]. These data are markedly different from those observed for butane autoxidation at low initiator concentrations, where temperatures up to 170 °C and higher are required and acetic acid is produced with 40% selectivity. Cyclohexane oxidation in the presence of cobalt(II) acetate in acetic acid gives adipic acid in one step as the main product with 75% selectivity at more than 80% cyclohexane conversion [2b]. The induction period... 

Surprisingly, alkanes containing tertiary C—H bonds showed poor reactivity in these reactions.2943 b 29Sa d Thus, isobutane was less reactive than n-butane, and methylcyclohexane less reactive than cyclohexane (cf., lower reactivity of cumene to toluene). In the series of normal alkanes, n-butane reacted faster than n-pentane. n-Undecane was unreactive. These results are inconsistent with a normal free radical autoxidation. The authors used the analogy with arene oxidations to postulate that formation of radical cations by electron transfer from the alkane to Co(III) was a critical factor ... 

According to Wittig and Lupin,160 the cyclic peroxide (151) is formed when a suspension of 1,4-dipotassium 1,1,4,4-tetraphenyl-butane in ether is treated with dry oxygen. The peroxide (152) is formed, though in small quantities, during the autoxidation of di-(p-anisyl)ethylene in benzaldehyde, by combination of two molecules of... 

Air oxidation of /i-butane to maleic anhydride is possible over vanadium phos(4tate and, remaiicably, a 60% selectivity is obtained at 85% conversion. In the gas phase oxidation, in conffast to the situation found in the liquid, n-allcanes are oxidized more rapidly than branched chain alkanes. This is because secondary radicals are more readily able to sustain a chain for branched alkanes the relatively stable tertiary radical is preferentially formed but fails to continue the chain process. Vanadium(V)/ manganese(II)/AcOH has been used as a catalyst for the autoxidation of cyclohexane to adipic acid, giving 25-30% yields after only 4 h. ... 

The combination of bis[(2,6-carboxyl-carboxylato)pyri-dine]iron(n) [Fe (DPAH)2] and O2 results in the rapid autoxidation of the iron complex and is essentially unreactive with hydrocarbon substrates (e.g. c-CeH ). However, the presence of excess PhNHNHPh gives a system that is a hydrocarbon monooxygenase (C-C6H12c-CeHuOH). The distribution of R H isomers from 2-Me-butane indicates a selectivity in the order =CH > =CH2 > -CH3 the relative reactivities per C H bond are 1.00, 0.29, and 0.05, respectively. With Fe (PA)2/HOOH Fenton chemistry in 1.8 1 py/HOAc, the relative reactivities are 1.00, 0.43, and 0.07, and the values for aqueous HO- are 1.00, 0.48, and 0.10. Thus, the reactive intermediate from the Fe (DPAH)2/02/PhNHNHPh system is more selective than Fenton-derived and free HO-. 

Instead of acetaldehyde, other aliphatic aldehydes such as propanal or butanal can be applied. Besides MEK, diethyl ketone or dibutyl ketone or even simply n-butane is used. It is worthwhile to point out the significant importance of co-oxi-dizing processes in the mechanistic course of autoxidation reactions. After a short induction time, the intermediates formed act as co-oxidants for the remaining starting molecules. 

Chain lengths are considerably longer for isobutane than for -butane because of the difference in the strengths of Ae tertiary and secondary C—H bonds yields of t-butyl hydroperoxide are, therefore, high. The -Bu02 radicals, formed by abstraction of a primary hydrogen from isobutane by f-BuO , play an important role in the autoxidation of this hydrocarbon. ... 

The cobalt-catalyzed autoxidation of toluene in acetic acid at 363 K is accelerated by butan-2-one and benzaldehyde because peroxy radicals play a minor role in ratecontrolling propagation reactions. High rates of autoxidation are also obtained in the presence of Br because bromine atoms are important chain-propagating species. ... 

As a part of their research prograirune on the chemistry of melanins. Swan and his group in Newcastle have recently studied the tyrosine catalysed and auto-oxidation of dopamine (19) and DOPA (3) and a number of related compounds [57-60]. This group has also investigated the oxidation of 2,4,5-trihydroxyphenylethylamine (20) and synthesised a number of dimeric catecholamines 5,5, 6,6 -tetrahydroxy biphenyl-3,3 -ylenedi(ethyla-mine) (21) 5,5, 6,6 -tetrahydroxybiphenyl-2,2 -ylenedi(ethylamine) (22) 5,5, 6,6 -tetrahydroxybiphenyl-2,3 -ylenedi(ethylamine) (23) 2,3-bis(3,4-dihydroxyphenyl)butane-l,4-diamine (24) and 5,5, 6,6 -tetrahydroxybi-phenyl-3,3 -ylenedialanine (25) [58] and studied their tyrosinase catalysed oxidation, autoxidation, and oxidation with silver oxide, to melanins [59]. 

Saturated and unsaturated hydrocarbons with odd and even numbers of carbon atoms in the molecule (about C11-C35) are present as the primary substances in all vegetable oils and animal fats. Alkanes, alkenes, alkadienes and alkatrienes also arise as oxidation products of unsaturated fatty acids, catalysed by lipoxygenases or by autoxidation of fatty acids during food storage and processing. Only the lower hydrocarbons can play a role as odour-active substances. The main hydrocarbons resulting from oxidation of unsaturated fatty acids are ethane from Hnolenic acid, pentane and butane from Hnoleic acid and hexane and octane from oleic acid. The immediate precursors of hydrocarbons are the fatty acid hydroperoxides (Table 8.4). The unsaturated hydrocarbons are predominantly (Z)-isomers. Numerous other hydrocarbons, including ahcycHc hydrocarbons, appear as secondary hpid oxidation products. 

Chien and Kiang [44] carried out oxidative pyrolysis of PP at temperatures between 240 °C and 289 °C. The products were separated by GC and identified online by an interface GC peak-identification system. The major products were CO, H O, acetaldehyde, acetone, butanal, formaldehyde, methanol and other ketones and aldehydes. These identifications were confirmed by MS. Most of the products can be accounted for by well-known reactions of alkoxyl and peroxyl radicals the major products are derived from the secondary alkoxy and peroxy species. Oxygen starvation is manifested in diffusion-limited products of olefins and dienes, and the increase in the formation of CO and H O in an atmosphere of pure oxygen. The first-order rate constant at 240 °C is 2.4 x 10 Vs, with an overall activation energy of approximately 16 kcal/mol (67 kj/mol). If one assumes that the oxidative pyrolysis shares the same reaction pathways as autoxidation at lower temperatures, then the observed rate constants and activation energy may be calculated from kinetic... 

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