Sources of Alkanes and Cycloalkanes

Distillation of crude oil yields a series of volatile fractions having the names indicated, along with a nonvolatile residue. The number of carbon atoms that characterize the hydrocarbons in each fraction is approximate. 

The word petroleum is derived from the Latin words for rock (petra) and oii (oleum). 

Although both are closely linked in our minds and by our own experience, the petroleum industry predated the automobile industry by half a century. The first oil well, drilled in Titusville, Pennsylvania, by Edwin Drake in 1859, provided rock oil, as it was then called, on a large scale. This was quickly followed by the development of a process to refine it so as to produce kerosene. As a fuel for oil lamps, kerosene burned with a bright, clean flame and soon replaced the more expensive whale oil then in use. Other oil fields were discovered, and uses for other petroleum products were found—illuminating gas lit city streets, and oil heated homes and powered locomotives. There were oil refineries long before there were automobiles. By the time the first Model T rolled off Henry Ford s assembly line in 1908, John D. Rockefeller s Standard Oil holdings had already made him one of the half-dozen wealthiest people in the world. 

Modem petroleum refining involves more than distillation, however, and includes two major additional operations  

The leaves and fruit of many plants bear a waxy coating made up of alkanes that prevents loss of water, hi addition to being present in beeswax (see Problem 2.5), hen-triacontane, CH3(CH2)29CH3, is a component of the wax of tobacco leaves. 

Cyclopentane and cyclohexane are present in petroleum, but as a rule, unsubsti- 

Although both are closely linked in our minds and by our own experience, the petroleum industry predated the automobile industry by half a century. The first oil well, drilled in Titusville, Pennsylvania, by Edwin Drake in 1859, provided rock oil, as it was then called, on a large scale. This was quickly followed by the development of a process to refine it so as to produce kerosene. As a fuel for oil lamps, kerosene 

Petroleum is not the only place where alkanes occur naturally. Solid n-alkanes, especially those with relatively long chains, have a waxy constituency and coat the outer surface of many living things where they help prevent the loss of water. Pentacosane [CH3(CH2)23CH3] is present in the waxy outer layer of most insects. Hentriacontane [CH3(CH2)29CH3] is a component of beeswax (see Problem 2.6) as well as the wax that coats the leaves of tobacco, peach trees, pea plants, and numerous others. The C23, C25, C27, C29, and C31 /2-alkanes have been identified in the surface coating of the eggs of honeybee queens. 

Cyclopentane and cyclohexane are present in petroleum, but as a rule, unsubstituted cycloalkanes are rarely found in natural sources. Compounds that contain rings of various types, however, are quite abundant. 

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Cycloalkane Nomenclature 75 Sources of Alkanes and Cycloalkanes 76 Physical Properties of Alkanes and Cycloalkanes 77... 

In this chapter we explored the three dimensional shapes of alkanes and cycloalkanes The most important point to be taken from the chapter is that a molecule adopts the shape that minimizes its total strain The sources of strain m alkanes and cycloalkanes are... 

Catalytic reforming92-94 of naphthas occurs by way of carbocationic processes that permit skeletal rearrangement of alkanes and cycloalkanes, a conversion not possible in thermal reforming, which takes place via free radicals. Furthermore, dehydrocyclization of alkanes to aromatic hydrocarbons, the most important transformation in catalytic reforming, also involves carbocations and does not occur thermally. In addition to octane enhancement, catalytic reforming is an important source of aromatics (see BTX processing in Section 2.5.2) and hydrogen. It can also yield isobutane to be used in alkylation. 

In the early stages of preparation of the present manuscript I was confronted with a surprise The analysis of alkanes and cycloalkanes has never been reviewed as such. Although the C—C and C—H bonds are the most abundant bonds in organic chemistry, the analysis of compounds constructed solely from these bonds cannot be found in analytical reviews of functional groups. Therefore, I could not relate to previous secondary or tertiary sources of literature. Moreover, the reader of this chapter will find that, although I attempted to stay as objective as possible in presenting the various analytical techniques, most of the advanced applications come from petroleum and other fossil fuels studies. Since the choice of analytical techniques relates to structures of the whole alkane or cycloalkane, the various isomers, enantiomers or conformations are discussed. 

The major source of saturated hydrocarbons (alkanes and cycloalkanes) in the geosphere is petroleum. Other fossil fuels, i.e. coal and bitumens, may have small fractions of alkanes and cycloalkanes. 

Photochemistry, by definition , deals with excitation energies ofA 40 nm (< 30 eV), whereas radiation chemistry (radiolysis) studies the photochemical effects of ionizing radiation (e.g. from radioactive sources or synchrotron radiation) such as the phenomenon of photoconductivity and the formation of alkane radical cations (RH ). In this chapter we will concentrate on photochemical reactions of alkanes and cycloalkanes and their rearrangements. We mainly considered the literature since 1980. 

As well as atmospheric sources, pyrolysis of fluorine-containing polymers, which may occur in engine oil additives, non-stick cookware or incinerated medical equipment (i.e. syringes) and household waste, may also produce TFA. This process may also produce perfluorinated alkanes and cycloalkanes, which have significant GWP, and have estimated tropospheric half-lives of more than 2000 years. Trifluoroacetate may also be produced by metabolism of trifluoromethyl-containing drugs such as Prozac, and anaesthetics including halothane and iso-fluorane [4],... 

Summary Rules for Naming Alkanes 94 3-4 Physical Properties of Alkanes 95 3-5 Uses and Sources of Alkanes 97 3-6 Reactions of Alkanes 99 3-7 Structure and Conformations of Alkanes 100 3-8 Conformations of Butane 104 3-9 Conformations of Higher Alkanes 106 3-10 Cycloalkanes 107 3-11 Cis-trans Isomerism in Cycloalkanes 109 3-12 Stabilities of Cycloalkanes Ring Strain 109 3-13 Cyclohexane Conformations 113... 

The principal source of alkanes is petroleum, together witl tl accompanying natural gas. Decay and millions of years of geologicarstresses have transformed the complicated organic compounds that once made up living plants or animals into a mixture of alkanes ranging in size from one carbon to 30 or 40 carbons. Formed along with the alkanes, and particularly abundant in California petroleum, are cycloalkanes (Chap. 9), known to the petroleum industry as naphthenes. 

In Ihif chaplcr we explored the thiee-dimensicDal shqies of alkanes aid cycloalkanes. The most importail point to be tsken frem the chqter is that a molecule adopts the shape that minimizes ils total strain. The sources of strain in alkanes and cycloat... 

Cycloalkanes have similar properties to those of alkanes, and they can also be used as sources of energy by burning them with O2. 

Naphthas, bp 20 to 200 °C, are a mixture of C5 to Cjg alkanes and cycloalkanes. Naphthas also contain small amounts of benzene, toluene, xylene, and other aromatic hydrocarbons (Chapter 9). The light naphtha fraction, bp 20 to 150°C, is the source of straight-run gasoline and averages approximately 25% of crude petroleum. In a sense, naphthas are the most valuable distillation fractions, because they are useful not only as fuel, but also as sources of raw materials for the organic chemical industry. 

The two most important natural sources of alkanes are petroleum and natural gas. Petroleum is a complex liquid mixture of organic compounds, many of which are alkanes or cycloalkanes. For more details about how petroleum is refined to obtain gasoline, fuel oil, and other useful substances, read A Word about Petroleum, Gasoline, and Octane Number on pages 102-103. 

Ethene (ethylene) can serve as a case study for the significance of alkenes in industrial chemistry. This monomer is the basis for the production of polyethene (polyethylene), millions of tons of which are manufactured in the United States annually. The major source of ethene is the pyrolysis of petroleum, or hydrocarbons derived from natural gas, such as ethane, propane, other alkanes, and cycloalkanes (Section 3-3). 

Alkanes have densities between 0.6 and 0.8 g/cm, so they are less dense than water. Thus gasoline, which is largely a mixture of alkanes, is less dense than water and floats on water. Pure alkanes are colorless, tasteless, and nearly odorless. However, gasoline has an odor and some color because dyes are added to gasoline by refiners to indicate its source and composition. Gasoline also contains compounds containing benzene rings, which have characteristic, unpleasant odors. Table 4.7 lists the physical properties of some common alkanes and cycloalkanes. 

Automotive gasoline contains 150 or more different chemical compounds and the relative concentrations of the compounds vary considerably, depending on the source of crude oil, refinery process, and product specifications. Typical hydrocarbon constituents are (volume basis) alkanes (4 to 8%), alkenes (2 to 5%), isoalkanes (25 to 40%), cycloalkanes (3 to 7%), cycloalkenes (1 to 4%), and aromatics (20 to 50%). However, these proportions vary greatly. 

Crude oil, however, has almost completely replaced coal as a source of aromatics. Crude oil contains several percents of benzene, toluene, and xylenes and their cycloalkane precursors. The conversion efficiency for preparing toluene or xylenes from their precursors is nearly 100%. For benzene this efficiency is slightly lower. Moreover, alkanes are also transformed to aromatics during refining processes, allowing efficient production of simple aromatic compounds. 

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