Chemistry
Oxidation of Alkanes
Oxidation of alkanes involves the reaction of alkanes with oxygen or other oxidizing agents to form products such as alcohols, aldehydes, or carboxylic acids. This process typically requires the presence of a catalyst and can be used to produce valuable chemical intermediates. Oxidation of alkanes is an important transformation in organic chemistry with various industrial applications.
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11 Key excerpts on "Oxidation of Alkanes"
eBook - PDF- John M. McIntosh(Author)
- 2018(Publication Date)
- De Gruyter(Publisher)
5 Reactions of Alkanes, Alkenes, and Alkynes 5.1 Introduction In the preceding four chapters you have been introduced to a wide range of basic prin-ciples that govern the structure, shape, and reactivity of organic molecules. We are fi-nally ready to start applying these principles to actual molecules and their reactions. In this chapter, we will look at some reactions of hydrocarbons, and particular atten-tion will be paid to alkenes . Some of the reactions we will see do not fit the general mechanistic types we will be developing and therefore must be learned separately. However, most will be considered from the viewpoint of what is actually happening as the molecules react: i.e., the mechanism. 5.2 Reactions of Alkanes This section will be quite brief simply because, on the usual scale of reactivities, alka-nes (saturated hydrocarbons) are quite unreactive. Furthermore, those reactions they do undergo do not fit the type of mechanistic pathways we will be considering. 5.2.1 Oxidation The most general reaction undergone by alkanes is combustion: i.e., their oxidation in air. For example CH 4 + 2O 2 → CO 2 + 2H 2 O + heat This, of course is the reaction that heats houses and powers internal combustion en-gines. It is also useful for determining the molecular formula of organic molecules (see Problem 2.4). The ultimate goal of any organic chemistry course is to be able to predict, from a knowledge of mechanism and/or by analogy with similar molecules, how a particular molecule will react under given conditions. It is strongly suggested that you start a list of the reactions we have discussed and keep it up-to-date, lecture by lecture. This will greatly simplify review. It is also important to realize that the reactions must be learned frontwards and backwards. That is – we will see a reac-tion where A gives B under certain conditions. You should remember this in terms of how A reacts and also how to prepare B. https://doi.org/10.1515/9783110565140-005
eBook - ePubBiocatalysis in Organic Synthesis
The Retrosynthesis Approach
- Nicholas J Turner, Luke Humphreys(Authors)
- 2018(Publication Date)
- Royal Society of Chemistry(Publisher)
Alkanes are saturated hydrocarbons, which makes them the lowest oxidation level of carbon atoms. They are highly important molecules, forming the basis of the chemical industry itself. They can be obtained from natural resources such as gas and crude oil and are also found in algae, bacteria and plants. They are used as a fuel to produce energy and converted into alkenes, which in turn are raw materials for products such as polymers, adhesives and detergents, as well as chemical synthesis. Chiral alcohols, formed by the Oxidation of Alkanes, are also valuable and are precursors for compounds used in agrochemicals, pharmaceuticals or liquid crystals. This makes the selective Oxidation of Alkanes to alcohols an important reaction for chemical synthesis. However, this reaction is challenging as carbon–hydrogen bonds are relatively inert with high activation energy, and for a substrate with many C–H bonds, obtaining high chemo-, regio- and stereoselectivity is a problem. In addition, the product alcohols are more easily oxidised than the starting material, so these reactions are difficult to control. In addition to chemical approaches, enzymes have been reported to catalyse the selective Oxidation of Alkanes to alcohols. These methods use mild conditions and green solvents, and the products can be obtained with high chemo-, regio- or stereoselectivity. In the next two sections, we will look at families of enzymes that are capable of performing these reactions.6.2.1 Oxidation of Alkanes with P450 Monooxygenases
One of the families of enzymes capable of catalysing the hydroxylation of alkanes is the P450 monooxygenases. As shown in Figure 6.2 , these enzymes use molecular oxygen and two electrons from a nicotinamide co-factor, which is the terminal reductant to carry out the hydroxylation.Figure 6.2 General transformation of alkane oxidation catalysed by P450 monooxygenases.There are many methods of producing alcohols, some of which are detailed in Figure 6.3
eBook - PDF- C.H. Bamford, R.G. Compton, C.F.H. Tipper†(Authors)
- 1980(Publication Date)
- Elsevier Science(Publisher)
Chapter 1 Kinetics and Mechanisms of Free Radical Oxida= tion of Alkanes and Olefms in the Liquid Phase THEODORE MILL and DALE G. HENDRY 1. Introduction Reactions of oxygen with organic compcunds occupy a central position in the scheme of living things, producing the energy that drives all bio- chemical machines and most of the mechanical and heat energy used in technology. Over a wide temperature range, bounded roughly by enzyme- mediated oxygenations at low temperatures and fast combustion reactions at high temperatures, are a host of relatively slow oxidation processes, involving free radicals, which are responsible for the conversion of hydro- carbons to useful industrial intermediates as well as unwanted degradation of lipids and polymers, and the intensification of environmental pollu- tion. The major objective of this chapter is to provide a critical review of the kinetics and mechanisms of free radical Oxidation of Alkanes and alkenes and the techniques for their measurement and determination under mild conditions in the liquid phase. A brief discussion of photooxygenation (singlet oxygen) reactions is included for completeness. Literature has been reilewed carefully through 1975 and updated with references to mid -1 97 8. Our principal concern is to utilize both kinetics and product formation as diagnostic tools for elucidating the detailed mechanisms of oxidation reactions in terms of elementary steps, rate coefficients, thermochemistry and structurereactivity relationships. Accordingly, our emphasis throughout the chapter will be on these relationships, exemplified by reac- tions of simple molecules and the way in which they may be used to inter- pret and predict the rates and products of oxidation reactions involving more complex molecules or extreme conditions *.
eBook - PDF- Chung K. Law(Author)
- 2010(Publication Date)
- Cambridge University Press(Publisher)
For example, the stoichiometric oxidation of one ----CH 2 ---- group in a typical aliphatic fuel molecule, ----CH 2 ---- + 1.5O 2 → H 2 O + CO 2 , releases about 156 kcal amount of heat per mole of CH 2 consumed. The extent of exothermicity represents one of the highest energy densities in the discipline of chemistry. As we discussed in Chapter 2, the conversion of a hydrocarbon fuel to products during combustion is rarely achieved in one step. Instead, it takes place through many stages of reaction, during which a variety of intermediates are produced. Some of them are radicals (e.g., H, O, and OH), which are extremely reactive due to the presence of unpaired electrons, and are short-lived during combustion. To under- stand the mechanism of hydrocarbon oxidation, it is necessary to first introduce the nomenclature and molecular structures of some of the important hydrocarbon fuels and the intermediates during their combustion. Alkanes (Paraffins): The molecules have open-chain, single-bond, saturated struc- tures with the general chemical formula C m H 2m+2 . The smallest alkane compound is methane (CH 4 ), which is the major component of natural gas. Alkanes can be further classified as normal alkanes with a straight-chain structure (e.g., n-butane) and iso-alkanes with one or more branched chains (e.g., i -butane, and 2,2,4-trimethylpentane, also known as iso-octane, which is a desirable gasoline fuel for its anti-knock property). C C H H H C H M H H H H C C C C H H H H H H H H H n-butane i-butane 86 Oxidation Mechanisms of Fuels C C H H H C C C H H M M H M H H H C H H H M : methyl group 2,2,4-trimethylpentane The molecular structures shown above indicate only the bonding structures of the molecules. They do not, however, reflect their true, three-dimensional geometric structure. In fact, the carbon atoms in an aliphatic compound are not connected in a linear fashion, but are zigzagged, with a C----C----C angle of about 109 degrees.
- Herman Pines(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
5 Oxidation I. INTRODUCTION The conversion of hydrocarbons to products containing oxygen is of great industrial importance. Many key organic compounds are formed by controlled oxidation of selected hydrocarbons. This chapter is limited principally to a discussion of the methods and mechanisms of catalytic ox-idation of hydrocarbons to compounds of major industrial importance. II. ALKANES: BUTANE (TO ACETIC ACID) The three major methods for producing acetic acid commercially con-sist of the oxidation of butane or low-boiling liquid petroleum hydrocar-bons with air in the presence of small amounts of cobalt or manganese salts, the carbonylation of methanol, as discussed in Chapter 6, Section ΙΙΙ,Β, and the oxidation of acetaldehyde, which is produced by the palla-dium-catalyzed oxidation of ethylene (Wacker process). In 1973 about 20% of all acetic acid produced in the U.S., or 2.5 x 10 8 kg, was formed by the oxidation of butane with air, with cobalt(III) acetate as catalyst. Under operating conditions of 60 atm and 180°C the conversion of butane was almost complete. The yield of acetic acid based on carbon ef-ficiency was 57%. By-products consisted of CO and C O z (17%) and esters and ketones (22%) (Lowry and Aquilo, 1974). This oxidation of butane proceeds by a radical chain reactipn. The co-balt ion is assumed to participate in the decomposition of sec-butyl hydro-peroxide, and it could possibly participate in the initial step as well. The main propagation step between the peroxy radical and butane does not seem to involve a metal ion. The aldehyde formed is oxidized in the pres-ence of the catalyst to acetic acid. The reaction is proposed to proceed according to the following steps: 213 214 5 Oxidation Initiation: C 4 H 10 + Co 3 -H 3 ° > H . + H + + CO 2 4 H 5 C 2 ^ Oxidation: H 3 Cv CH- + 0 2 H 3 C> HrCo^ CHOO.
eBook - PDFMetal Oxides
Chemistry and Applications
- J.L.G. Fierro(Author)
- 2005(Publication Date)
- CRC Press(Publisher)
15 Oxidative Dehydrogenation (ODH) of Alkanes over Metal Oxide Catalysts G. Deo, M. Cherian, and T.V.M. Rao Department of Chemical Engineering, Indian Institute of Technology, Kanpur, India C ONTENTS 15.1 Introduction ............................................................... 491 15.2 Mechanisms of the ODH Reactions ..................................... 493 15.3 Metal Oxide Catalysts Used for ODH Reactions ....................... 498 15.3.1 ODH of Ethane ................................................... 498 15.3.2 ODH of Propane .................................................. 502 15.3.3 ODH of n -Butane ................................................ 504 15.3.4 ODH of Isobutane ............................................... 506 15.3.5 Summary ......................................................... 507 15.4 Conclusions ............................................................... 510 References ....................................................................... 510 15.1 I NTRODUCTION Conversion of lower alkanes (ethane, propane, and butanes) to organic compounds of industrial importance is a daunting task. This is due to the poor reactivity of the C–H bond. Furthermore, the industrially important product(s) is usually more reactive than the alkane itself. Selective catalytic oxidation using oxygen is one of the simplest ways of converting alkanes, especially the lower alkanes, into useful intermediates of the petrochemical industry. Since it is selective under normal con-ditions and in the presence of air, thermodynamics suggests that undesirable CO 2 is the only stable compound formed; though at higher temperatures CO, which is also undesirable, is also stable [1]. Consequently, all organic materials in the pres-ence of air are only metastable intermediates to carbon oxides. The challenge is, 491
- T. J. Donohoe, Norbert Krause, S. P. Marsden, T. J. Donohoe, Norbert Krause, S. P. Marsden(Authors)
- 2022(Publication Date)
- Thieme(Publisher)
217 26.1. 2 Synthesis of Ketones by Oxidation of Alkenes and Alkanes Table 24 (cont.) Entry Starting Material Products Ratio a (Secondary/Tertiary) Ref 4 H H H H OH 6% H HO H H O 13% 81% 87:13 c (80:20) [62] a Ratio [(all secondary alcohols plus ketones)/all tertiary alcohols] determined by GC analysis; numbers in parentheses are theoretically calculated values as statistic average for all secondary and tertiary C -H bonds. b Ratio ( cis -9-Decalol/ trans -9-Decalol) = 20:80. c Ratio ( cis -9-Decalol/ trans -9-Decalol) = 28:72. Ketones (Table 24); General Procedure: [62] CAUTION: Concentrated hydrogen peroxide solutions are explosively decomposed by traces of transition-metal ions and a prior reductive workup should be carefully considered for larger scales. Photocatalytic experiments were conducted under visible-light irradiation through a cut-off filter ( l > 420 nm) with a 500-W halogen lamp as the visible-light source. The light source was positioned inside a cylindrical vessel that was surrounded by a jacket that con-tained circulating water to cool the lamp. H 2 O 2 (0.15 mmol, 0.04 equiv) was added to a vig-orously stirred soln of iron complex 75 (0.004 mmol, 0.1 mol%) and a cyclohexane sub-strate (4 mmol) in MeCN/H 2 O (6:4; 2.5 mL) over ca. 45–75 s. The mixture was irradiated for 20 h at rt and then extracted with Et 2 O. The extract was dried (MgSO 4 ) and then sub-jected to GC using bromobenzene as internal standard. 26.1. 2.5.8 Oxidation of Alkanes by Heterogeneous Catalysis Heterogeneous catalysis occurs at or near the interface of catalyst and reactants. [63,64] This section covers the use of metal–organic frameworks in catalysis. [65] The application of solid-supported catalysts offers the possibility of catalyst recovery and recycling, and the potential to employ flow reactors.
eBook - PDF- R.G. Compton, C.H. Bamford, C.F.H. Tipper†(Authors)
- 1977(Publication Date)
- Elsevier Science(Publisher)
Finally, the variation of the mechanism with the molecular weight and structure of the hydrocarbon will be discussed. 2. The prevalent theories on the mechanism of hydrocarbon oxidation in 1960 An excellent review of the development of research on the gas-phase oxidation of hydrocarbons from the end of the nineteenth century was published in 1960 by Shtern [2]. In common with many monographs it was not entirely unbiased, but nevertheless gave an up-to-date account of the current views on the mechanism of the gaseous oxidation of hydro- carbons at that time. Kinetically it is of course one of the best known degenerately branched-chain reactions, the theory of which has been developed in full by Semenov [3]. For the slow oxidation of hydro- carbons (X,) at pressures up to 380-760 torr and in the temperature range 200-600 OC the overall chemical mechanism was thought to involve two major routes, namely strict oxidation, which led to the formation of oxygen-containing products (aldehydes, alcohols, ketones, acids and carbon oxides) and cracking, which led to the formation of hydrogen and unsaturated and saturated hydrocarbons of a lower molecular weight than the initial fuel. The general mechanism of the oxidation route was summarized by Shtern as shown in Scheme 1. The alkyl radical initially formed reacts readily with oxygen to give the corresponding alkylperoxy radical, which may abstract hydrogen from a fuel molecule to form the alkylhydroperoxide or alternatively decompose to yield an aldehyde and an alkoxy radical.
- Kilian Muñiz(Author)
- 2018(Publication Date)
- Thieme(Publisher)
[78] Zhu, L.; Yu, H.; Xu, Z.; Jiang, X.; Lin, L.; Wang, R., Org. Lett. , (2014) 16 , 1562. [79] Zhu, R.; Buchwald, S. L., J. Am. Chem. Soc. , (2015) 137 , 8069. [80] Schmidt, V. A.; Alexanian, E. J., J. Am. Chem. Soc. , (2011) 133 , 11 402. 388 Catalytic Oxidation 5 Oxidation of Alkenes 5.4 Halogenation and Halocyclization of Alkenes A. Andries-Ulmer and T. Gulder General Introduction Oxidative halogenation reactions comprise a plethora of different transformations such as the Æ -halogenation of carbonyl compounds and the electrophilic halofunctionalization of alkenes. The latter reaction constitutes one of the oldest methods for the functionaliza-tion of substrates, and found its way into textbooks already in the 1930s. Since then, ha-logenations and halocyclizations of alkenes have become workhorses in organic synthe-sis. They are among the most practical, predictable, and significant reactions, giving rise to a manifold of very useful products. With the carbon — halogen bond (C — Cl, C — Br, C — I) strength being relatively low, halogen atoms serve as good handles for further chemical manipulations, such as substitutions or cross-coupling reactions. In addition to their ver-satility as synthetic building blocks, halogenated compounds themselves also play an im-portant role as pharmaceuticals, agrochemicals, and materials. Electrophilic halofunctionalizations of C = C bonds are, in general, highly stereospe-cific processes, following the widely accepted mechanism shown in Scheme 1. The reac-tion characteristically starts with the formation of a halogen–alkene ð -complex 2 , which is converted into the haliranium ion 3 upon ionization. The existence of such cyclic inter-mediates 3 was proposed by Roberts and Kimball in 1937 to explain the obtained diaste-reoselectivity in the chlorination and bromination of alkenes 1 . [1] Extensive low-temper-ature NMR studies by Olah and co-workers proved this hypothesis in the late 1960s.
- Penny A Chaloner(Author)
- 2013(Publication Date)
- Butterworth-Heinemann(Publisher)
Some examples are given in Figure 65. 6.9 Oxidation of saturated hydrocarbons. Oxidation of saturated hydrocarbons occurs mainly by a radical mechanism, is unselective, and requires extreme conditions. Metal complexes as initiators provide some acceleration but selectivity usually remains low. For example, alkanes are hydroxylated in the presence of Co(OAc) 2 / HOAc/0 2 . Methane is converted to methanol and methyl chloride using H 2 PtCl 6 /02 in a stoichiometric process and the use of NaίHPMogVgO^Q as a relay for reoxidation permits a catalytic reaction. 452 Butane is oxidised at 170° to give a variety of products with 40% selectivity to acetic acid, in the presence of various metal ions. Using Co(0Ac) 2 /butanone allows the reaction to occur at 100°- 125° and selectivity to HOAc rises to 83%. 453 564 Ref. V 0 2 5 ArMe + 0 } ArCOOH 4 4 8 HBr Phl(OAc) PhCH Ph > PhCOPh 449 Ru(II) I0 4 £ CH 3 C 6 H 4 CH 3 * P-CH C H COOH 449 Ru(II) d ° * (Ph P) RhCl PhCH 2 CH 3 + 0 2 ± > PhCOCH 3 450 (Ph 3 P) 3 RhCl + o 2 , u ^ — ^-48% Me(T ^ ^ MeO 451 Figure 65 Other metal complexes as catalysts for alkyl arene oxidation. A certain measure of selectivity is achieved in the presence of metal tetraphenylporphyrin complexes. Both ROOH and PhIO have been used as oxidants and heptane is conveted to 2-, 3- and 4-heptanols and heptanones. Yields do not depend strongly on the ligand using ROOH, but with PhIO the nature of the aryl ring is relevant. This is explained by the mechanisms of Figure 66.^» 455 Tertiary CH bonds are curiously unreactive; iso-butane is less reactive than n-butane. This has been interpreted in terms of rate-limiting electron transfer (equation (106)); however, many anomalies exist. 565 M + ROOH » MOH + RO' RO # + R'H * R»' + ROH R·· + MOH » R'OH + M M + PhlO » M=0 + Phi M=0 + R»H f MOH + R' # R· ' + MOH £ R'OH + M M = tetraphenylporphyrin metal complex Figure 66 Mechanisms of alkane oxidation in the presence of metal tetraphenylporphyrin complexes.
- Evgeny T. Denisov, Igor B. Afanas'ev(Authors)
- 2005(Publication Date)
- CRC Press(Publisher)
The situation is different in the case of chain reaction. The change in temperature and other conditions not only change the reaction rate but can change the mechanism of the reaction and composition of the formed products. This can be illustrated by analysis of the mechanism of the hydrocarbon oxidation at different temperatures, concentration of the reactants, and the rates of initiation [288]. Varying the conditions of oxidation, the mechanism and products of the reaction can be changed. The traditional chain oxidation with chain propagation via the reaction RO 2 . þ RH occurs at a sufficiently elevated temperature when chain propagation is more rapid than chain termination (see earlier discussion). The main molecular product of this reaction is hydroperoxide. When tertiary peroxyl radicals react more rapidly in the reaction RO 2 . þ RO 2 . with formation of alkoxyl radicals than in the reaction RO 2 . þ RH, the mechanism of oxidation changes. Alkoxyl radicals are very reactive. They react with parent hydrocarbon and alcohols formed as primary products of hydrocarbon chain oxidation. As we see, alkoxyl radicals decompose with production of carbonyl compounds. The activation energy of their decomposition is higher than the reaction with hydrocarbons (see earlier discussion). As a result, heating of the system leads to conditions when the alkoxyl radical decomposition occurs more rapidly than the abstraction of the hydrogen atom from the hydrocarbon. The new chain mechanism of the hydrocarbon oxidation occurs under such conditions, with chain 72 Oxidation and Antioxidants in Organic Chemistry and Biology TABLE 2.20 Rate Constants of Reactions R 1 O . 1 RH ! R 1 OH 1 R . (Selected Experimental Data) RH Solvent T (K) k (L mol 2 1 s 2 1 ) Ref.
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