Benzene is an organic chemical compound with the molecular formula C 6 H 6 . The benzene molecule is composed of six carbon atoms joined in a planar hexagonal ring with one hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon .
156-548: Benzene is a natural constituent of petroleum and is one of the elementary petrochemicals . Due to the cyclic continuous pi bonds between the carbon atoms, benzene is classed as an aromatic hydrocarbon . Benzene is a colorless and highly flammable liquid with a sweet smell, and is partially responsible for the aroma of gasoline . It is used primarily as a precursor to the manufacture of chemicals with more complex structures, such as ethylbenzene and cumene , of which billions of kilograms are produced annually. Although benzene
312-423: A hierarchy . Two chemicals might be the same constitutional isomer, but upon deeper analysis be stereoisomers of each other. Two molecules that are the same stereoisomer as each other might be in different conformational forms or be different isotopologues . The depth of analysis depends on the field of study or the chemical and physical properties of interest. The English word "isomer" ( / ˈ aɪ s əm ər / )
468-403: A trans isomer where the two chlorines are on the same plane as the two carbons, but with oppositely directed bonds; and two gauche isomers, mirror images of each other, where the two − CH 2 Cl {\displaystyle {\ce {-CH2Cl}}} groups are rotated about 109° from that position. The computed energy difference between trans and gauche
624-399: A "parent" molecule (propane, in that case). There are also three structural isomers of the hydrocarbon C 3 H 4 {\displaystyle {\ce {C3H4}}} : In two of the isomers, the three carbon atoms are connected in an open chain, but in one of them ( propadiene or allene; I ) the carbons are connected by two double bonds , while in
780-979: A circle inside a hexagonal arrangement of carbon atoms. Derivatives of benzene occur sufficiently often as a component of organic molecules, so much so that the Unicode Consortium has allocated a symbol in the Miscellaneous Technical block with the code U+232C (⌬) to represent it with three double bonds, and U+23E3 (⏣) for a delocalized version. Many important chemical compounds are derived from benzene by replacing one or more of its hydrogen atoms with another functional group . Examples of simple benzene derivatives are phenol , toluene , and aniline , abbreviated PhOH, PhMe, and PhNH 2 , respectively. Linking benzene rings gives biphenyl , C 6 H 5 –C 6 H 5 . Further loss of hydrogen gives "fused" aromatic hydrocarbons, such as naphthalene , anthracene , phenanthrene , and pyrene . The limit of
936-554: A conformation isomer is separated from any other isomer by an energy barrier : the amount that must be temporarily added to the internal energy of the molecule in order to go through all the intermediate conformations along the "easiest" path (the one that minimizes that amount). A classic example of conformational isomerism is cyclohexane . Alkanes generally have minimum energy when the C − C − C {\displaystyle {\ce {C-C-C}}} angles are close to 110 degrees. Conformations of
1092-520: A fluid resembling petroleum, which when treated in the same way as the seep oil gave similar products. Young found that by slow distillation he could obtain several useful liquids from it, one of which he named "paraffine oil" because at low temperatures it congealed into a substance resembling paraffin wax. The production of these oils and solid paraffin wax from coal formed the subject of his patent dated October 17, 1850. In 1850, Young & Meldrum and Edward William Binney entered into partnership under
1248-498: A gasoline additive in some nations. In the United States , concern over its negative health effects and the possibility of benzene entering the groundwater has led to stringent regulation of gasoline's benzene content, with limits typically around 1%. European petrol specifications now contain the same 1% limit on benzene content. The United States Environmental Protection Agency introduced new regulations in 2011 that lowered
1404-551: A gasoline additive, or routed through an extraction process to recover BTX aromatics (benzene, toluene and xylenes). Although of no commercial significance, many other routes to benzene exist. Phenol and halobenzenes can be reduced with metals. Benzoic acid and its salts undergo decarboxylation to benzene. The reaction of the diazonium compound derived from aniline with hypophosphorus acid gives benzene. Alkyne trimerisation of acetylene gives benzene. Complete decarboxylation of mellitic acid gives benzene. Benzene
1560-428: A left hand and a right hand. The two shapes are said to be chiral . A classical example is bromochlorofluoromethane ( CHFClBr {\displaystyle {\ce {CHFClBr}}} ). The two enantiomers can be distinguished, for example, by whether the path F ⟶ Cl ⟶ Br {\displaystyle {\ce {F->Cl->Br}}} turns clockwise or counterclockwise as seen from
1716-516: A method from LPG (mainly propane and butane) to aromatics. Toluene hydrodealkylation converts toluene to benzene. In this hydrogen-intensive process, toluene is mixed with hydrogen, then passed over a chromium , molybdenum , or platinum oxide catalyst at 500–650 °C and 20–60 atm pressure. Sometimes, higher temperatures are used instead of a catalyst (at the similar reaction condition). Under these conditions, toluene undergoes dealkylation to benzene and methane : This irreversible reaction
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#17327808341221872-424: A mixture of hydrocarbons with boiling points between 60 and 200 °C is blended with hydrogen gas and then exposed to a bifunctional platinum chloride or rhenium chloride catalyst at 500–525 °C and pressures ranging from 8–50 atm. Under these conditions, aliphatic hydrocarbons form rings and lose hydrogen to become aromatic hydrocarbons. The aromatic products of the reaction are then separated from
2028-428: A molecule that are connected by just one single bond can rotate about that bond. While the bond itself is indifferent to that rotation, attractions and repulsions between the atoms in the two parts normally cause the energy of the whole molecule to vary (and possibly also the two parts to deform) depending on the relative angle of rotation φ between the two parts. Then there will be one or more special values of φ for which
2184-547: A molecule. Therefore, the possible isomers of a compound in solution or in its liquid and solid phases many be very different from those of an isolated molecule in vacuum. Even in the gas phase, some compounds like acetic acid will exist mostly in the form of dimers or larger groups of molecules, whose configurations may be different from those of the isolated molecule. Two compounds are said to be enantiomers if their molecules are mirror images of each other, that cannot be made to coincide only by rotations or translations – like
2340-512: A much shallower level. The Athabasca oil sands are one example of this. An alternative mechanism to the one described above was proposed by Russian scientists in the mid-1850s, the hypothesis of abiogenic petroleum origin (petroleum formed by inorganic means), but this is contradicted by geological and geochemical evidence. Abiogenic sources of oil have been found, but never in commercially profitable amounts. "The controversy isn't over whether abiogenic oil reserves exist," said Larry Nation of
2496-476: A process known as catagenesis . Formation of petroleum occurs from hydrocarbon pyrolysis in a variety of mainly endothermic reactions at high temperatures or pressures, or both. These phases are described in detail below. In the absence of plentiful oxygen, aerobic bacteria were prevented from decaying the organic matter after it was buried under a layer of sediment or water. However, anaerobic bacteria were able to reduce sulfates and nitrates among
2652-423: A real compound; they are fictions devised as a way to describe (by their "averaging" or "resonance") the actual delocalized bonding of o -xylene, which is the single isomer of C 8 H 10 {\displaystyle {\ce {C8H10}}} with a benzene core and two methyl groups in adjacent positions. Stereoisomers have the same atoms or isotopes connected by bonds of
2808-430: A set of parallel reactions, and oil eventually breaks down to natural gas by another set of reactions. The latter set is regularly used in petrochemical plants and oil refineries . Isomer In chemistry , isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism refers to
2964-665: A significant amount of petroleum while drilling for lignite in Wietze , Germany. Wietze later provided about 80% of German consumption in the Wilhelminian Era. The production stopped in 1963, but Wietze has hosted a Petroleum Museum since 1970. Oil sands have been mined since the 18th century. In Wietze in lower Saxony, natural asphalt/bitumen has been explored since the 18th century. Both in Pechelbronn as in Wietze,
3120-638: A single isomer, depending on the temperature and the context. For example, the two conformations of cyclohexane convert to each other quite rapidly at room temperature (in the liquid state), so that they are usually treated as a single isomer in chemistry. In some cases, the barrier can be crossed by quantum tunneling of the atoms themselves. This last phenomenon prevents the separation of stereoisomers of fluorochloroamine NHFCl {\displaystyle {\ce {NHFCl}}} or hydrogen peroxide H 2 O 2 {\displaystyle {\ce {H2O2}}} , because
3276-574: A source of internal and inter-state conflict, leading to both state-led wars and other resource conflicts . Production of petroleum is estimated to reach peak oil before 2035 as global economies lower dependencies on petroleum as part of climate change mitigation and a transition towards renewable energy and electrification . The word petroleum comes from Medieval Latin petroleum (literally 'rock oil'), which comes from Latin petra 'rock' (from Greek pétra πέτρα ) and oleum 'oil' (from Greek élaion ἔλαιον ). The origin of
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#17327808341223432-411: A variety of liquid, gaseous, and solid components. Lighter hydrocarbons are the gases methane , ethane , propane and butane . Otherwise, the bulk of the liquid and solids are largely heavier organic compounds, often hydrocarbons (C and H only). The proportion of light hydrocarbons in the petroleum mixture varies among oil fields . An oil well produces predominantly crude oil. Because the pressure
3588-526: A visit to Fort Duquesne in 1750. Early British explorers to Myanmar documented a flourishing oil extraction industry based in Yenangyaung that, in 1795, had hundreds of hand-dug wells under production. Merkwiller-Pechelbronn is said to be the first European site where petroleum has been explored and used. The still active Erdpechquelle, a spring where petroleum appears mixed with water has been used since 1498, notably for medical purposes. There
3744-400: A wider liquid range. Toluene is also processed into benzene. As a gasoline (petrol) additive, benzene increases the octane rating and reduces knocking . As a consequence, gasoline often contained several percent benzene before the 1950s, when tetraethyl lead replaced it as the most widely used antiknock additive. With the global phaseout of leaded gasoline, benzene has made a comeback as
3900-554: A year before Drake's Pennsylvania operation and could be argued to be the first commercial oil well in North America. The discovery at Oil Springs touched off an oil boom which brought hundreds of speculators and workers to the area. Advances in drilling continued into 1862 when local driller Shaw reached a depth of 62 metres using the spring-pole drilling method. On January 16, 1862, after an explosion of natural gas , Canada's first oil gusher came into production, shooting into
4056-588: Is (1) to ensure that the worker can escape from a given contaminated environment in the event of failure of the respiratory protection equipment and (2) is considered a maximum level above which only a highly reliable breathing apparatus providing maximum worker protection is permitted. In September 1995, NIOSH issued a new policy for developing recommended exposure limits (RELs) for substances, including carcinogens. As benzene can cause cancer, NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding
4212-439: Is 5 ppm for 15 minutes. These legal limits were based on studies demonstrating compelling evidence of health risk to workers exposed to benzene. The risk from exposure to 1 ppm for a working lifetime has been estimated as 5 excess leukemia deaths per 1,000 employees exposed. (This estimate assumes no threshold for benzene's carcinogenic effects.) OSHA has also established an action level of 0.5 ppm to encourage even lower exposures in
4368-446: Is a back-formation from "isomeric", which was borrowed through German isomerisch from Swedish isomerisk ; which in turn was coined from Greek ἰσόμερoς isómeros , with roots isos = "equal", méros = "part". Structural isomers have the same number of atoms of each element (hence the same molecular formula ), but the atoms are connected in distinct ways. For example, there are three distinct compounds with
4524-420: Is a major industrial chemical , it finds limited use in consumer items because of its toxicity. Benzene is a volatile organic compound . Benzene is classified as a carcinogen . Its particular effects on human health , such as the long-term results of accidental exposure, have been reported on by news organizations such as The New York Times . For instance, a 2022 article stated that benzene contamination in
4680-460: Is accompanied by an equilibrium side reaction that produces biphenyl (aka diphenyl) at higher temperature: If the raw material stream contains much non-aromatic components (paraffins or naphthenes), those are likely decomposed to lower hydrocarbons such as methane, which increases the consumption of hydrogen. A typical reaction yield exceeds 95%. Sometimes, xylenes and heavier aromatics are used in place of toluene, with similar efficiency. This
4836-411: Is associated with include: acute myeloid leukemia (AML), aplastic anemia, myelodysplastic syndrome (MDS), acute lymphoblastic leukemia (ALL), and chronic myeloid leukemia (CML). Carcinogenic activity of benzene was discovered by Swedish pharmacologist C. G. Santesson [ se ] in 1897 on female workers of a tire-making factory. The American Petroleum Institute (API) stated in 1948 that "it
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4992-491: Is called diagenesis , a word that means a transformation of materials by dissolution and recombination of their constituents. Kerogen formation continued to a depth of about 1 km from the Earth's surface where temperatures may reach around 50 °C . Kerogen formation represents a halfway point between organic matter and fossil fuels : kerogen can be exposed to oxygen, oxidize and thus be lost, or it could be buried deeper inside
5148-583: Is caused by benzene. IARC rated benzene as "known to be carcinogenic to humans" ( Group 1 ). As benzene is ubiquitous in gasoline and hydrocarbon fuels that are in use everywhere, human exposure to benzene is a global health problem. Benzene targets the liver, kidney, lung, heart and brain and can cause DNA strand breaks and chromosomal damage, hence is teratogenic and mutagenic . Benzene causes cancer in animals including humans. Benzene has been shown to cause cancer in both sexes of multiple species of laboratory animals exposed via various routes. According to
5304-410: Is caused by electron delocalization : the electrons for C=C bonding are distributed equally between each of the six carbon atoms. Benzene has 6 hydrogen atoms, fewer than the corresponding parent alkane , hexane , which has 14. Benzene and cyclohexane have a similar structure, only the ring of delocalized electrons and the loss of one hydrogen per carbon distinguishes it from cyclohexane. The molecule
5460-726: Is considered a sticky, black, tar-like form of crude oil which is so thick and heavy that it must be heated or diluted before it will flow. Venezuela also has large amounts of oil in the Orinoco oil sands , although the hydrocarbons trapped in them are more fluid than in Canada and are usually called extra heavy oil . These oil sands resources are called unconventional oil to distinguish them from oil which can be extracted using traditional oil well methods. Between them, Canada and Venezuela contain an estimated 3.6 trillion barrels (570 × 10 ^ m ) of bitumen and extra-heavy oil, about twice
5616-569: Is found in geological formations . The term petroleum refers both to naturally occurring unprocessed crude oil, as well as to petroleum products that consist of refined crude oil. Conventional reserves of petroleum are primarily recovered by drilling , which is done after a study of the relevant structural geology , analysis of the sedimentary basin , and characterization of the petroleum reservoir . There are also unconventional reserves such as oil sands and oil shale which are recovered by other means such as fracking . Once extracted, oil
5772-481: Is generally considered that the only absolutely safe concentration for benzene is zero". There is no safe exposure level; even tiny amounts can cause harm. The US Department of Health and Human Services (DHHS) classifies benzene as a human carcinogen. Long-term exposure to excessive levels of benzene in the air causes leukemia, a potentially fatal cancer of the blood-forming organs. In particular, acute myeloid leukemia or acute nonlymphocytic leukemia (AML & ANLL)
5928-407: Is hepatically metabolized and excreted in the urine . Measurement of air and water levels of benzene is accomplished through collection via activated charcoal tubes, which are then analyzed with a gas chromatograph . The measurement of benzene in humans can be accomplished via urine , blood , and breath tests ; however, all of these have their limitations because benzene is rapidly metabolized in
6084-473: Is lower at the surface than underground, some of the gas will come out of solution and be recovered (or burned) as associated gas or solution gas . A gas well produces predominantly natural gas . However, because the underground temperature is higher than at the surface, the gas may contain heavier hydrocarbons such as pentane, hexane , and heptane (" natural-gas condensate ", often shortened to condensate. ) Condensate resembles gasoline in appearance and
6240-461: Is not another isomer, since the difference between it and 1-propanol is not real; it is only the result of an arbitrary choice in the direction of numbering the carbons along the chain. For the same reason, "ethoxymethane" is the same molecule as methoxyethane, not another isomer. 1-Propanol and 2-propanol are examples of positional isomers , which differ by the position at which certain features, such as double bonds or functional groups , occur on
6396-440: Is not chiral: the mirror image of its molecule is also obtained by a half-turn about a suitable axis. Another example of a chiral compound is 2,3-pentadiene H 3 C − CH = C = CH − CH 3 {\displaystyle {\ce {H3C-CH=C=CH-CH3}}} a hydrocarbon that contains two overlapping double bonds. The double bonds are such that
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6552-756: Is now called the Drake Well in Cherrytree Township, Pennsylvania .There also was a company associated with it, and it sparked a major oil drilling boom. The first commercial oil well in Canada became operational in 1858 at Oil Springs, Ontario (then Canada West ). Businessman James Miller Williams dug several wells between 1855 and 1858 before discovering a rich reserve of oil four metres below ground. Williams extracted 1.5 million litres of crude oil by 1860, refining much of it into kerosene lamp oil. Williams's well became commercially viable
6708-478: Is often called "on-purpose" methodology to produce benzene, compared to conventional BTX (benzene-toluene-xylene) extraction processes. Toluene disproportionation ( TDP ) is the conversion of toluene to benzene and xylene . Given that demand for para -xylene ( p -xylene ) substantially exceeds demand for other xylene isomers, a refinement of the TDP process called Selective TDP (STDP) may be used. In this process,
6864-565: Is on "this side" or "the other side" of the ring's mean plane. Discounting isomers that are equivalent under rotations, there are nine isomers that differ by this criterion, and behave as different stable substances (two of them being enantiomers of each other). The most common one in nature ( myo -inositol) has the hydroxyls on carbons 1, 2, 3 and 5 on the same side of that plane, and can therefore be called cis -1,2,3,5- trans -4,6-cyclohexanehexol. And each of these cis - trans isomers can possibly have stable "chair" or "boat" conformations (although
7020-419: Is planar. The molecular orbital description involves the formation of three delocalized π orbitals spanning all six carbon atoms, while the valence bond description involves a superposition of resonance structures . It is likely that this stability contributes to the peculiar molecular and chemical properties known as aromaticity . To reflect the delocalized nature of the bonding, benzene is often depicted with
7176-433: Is practiced on a large scale industrially. In the absence of the catalyst, benzene is impervious to hydrogen. Hydrogenation cannot be stopped to give cyclohexene or cyclohexadienes as these are superior substrates. Birch reduction , a non catalytic process, however selectively hydrogenates benzene to the diene. Benzene is an excellent ligand in the organometallic chemistry of low-valent metals. Important examples include
7332-435: Is rather low (~8 kJ /mol). This steric hindrance effect is more pronounced when those four hydrogens are replaced by larger atoms or groups, like chlorines or carboxyls . If the barrier is high enough for the two rotamers to be separated as stable compounds at room temperature, they are called atropisomers . Large molecules may have isomers that differ by the topology of their overall arrangement in space, even if there
7488-436: Is refined and separated, most easily by distillation , into innumerable products for direct use or use in manufacturing. Products include fuels such as gasoline (petrol), diesel , kerosene and jet fuel ; asphalt and lubricants ; chemical reagents used to make plastics ; solvents , textiles , refrigerants , paint , synthetic rubber , fertilizers , pesticides , pharmaceuticals , and thousands of others. Petroleum
7644-604: Is restricted by a somewhat rigid framework of other atoms. For example, in the cyclic alcohol inositol ( CHOH ) 6 {\displaystyle {\ce {(CHOH)6}}} (a six-fold alcohol of cyclohexane), the six-carbon cyclic backbone largely prevents the hydroxyl − OH {\displaystyle {\ce {-OH}}} and the hydrogen − H {\displaystyle {\ce {-H}}} on each carbon from switching places. Therefore, one has different configurational isomers depending on whether each hydroxyl
7800-451: Is similar in composition to some volatile light crude oils . The hydrocarbons in crude oil are mostly alkanes , cycloalkanes and various aromatic hydrocarbons , while the other organic compounds contain nitrogen , oxygen , and sulfur , and traces of metals such as iron, nickel, copper and vanadium . Many oil reservoirs contain live bacteria. The exact molecular composition of crude oil varies widely from formation to formation but
7956-504: Is sufficiently nucleophilic that it undergoes substitution by acylium ions and alkyl carbocations to give substituted derivatives. The most widely practiced example of this reaction is the ethylation of benzene. Approximately 24,700,000 tons were produced in 1999. Highly instructive but of far less industrial significance is the Friedel-Crafts alkylation of benzene (and many other aromatic rings) using an alkyl halide in
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#17327808341228112-455: Is the ether methoxyethane (ethyl-methyl-ether; III ). Unlike the other two, it has the oxygen atom connected to two carbons, and all eight hydrogens bonded directly to carbons. It can be described by the condensed formula H 3 C − CH 2 − O − CH 3 {\displaystyle {\ce {H3C-CH2-O-CH3}}} . The alcohol "3-propanol"
8268-426: Is true if a center with six or more equivalent bonds has two or more substituents. For instance, in the compound PF 4 Cl {\displaystyle {\ce {PF4Cl}}} , the bonds from the phosphorus atom to the five halogens have approximately trigonal bipyramidal geometry . Thus two stereoisomers with that formula are possible, depending on whether the chlorine atom occupies one of
8424-473: Is used in manufacturing a vast variety of materials essential for modern life, and it is estimated that the world consumes about 100 million barrels (16 million cubic metres ) each day. Petroleum production played a key role in industrialization and economic development. Some countries, known as petrostates , gained significant economic and international power over their control of oil production and trade. Petroleum exploitation can be damaging to
8580-484: Is used mainly as an intermediate to make other chemicals, above all ethylbenzene (and other alkylbenzenes ), cumene , cyclohexane , and nitrobenzene . In 1988 it was reported that two-thirds of all chemicals on the American Chemical Society 's lists contained at least one benzene ring. More than half of the entire benzene production is processed into ethylbenzene, a precursor to styrene , which
8736-538: Is used to make polymers and plastics like polystyrene . Some 20% of the benzene production is used to manufacture cumene, which is needed to produce phenol and acetone for resins and adhesives. Cyclohexane consumes around 10% of the world's benzene production; it is primarily used in the manufacture of nylon fibers, which are processed into textiles and engineering plastics. Smaller amounts of benzene are used to make some types of rubbers , lubricants , dyes , detergents , drugs , explosives , and pesticides . In 2013,
8892-412: Is ~1.5 kcal/mol, the barrier for the ~109° rotation from trans to gauche is ~5 kcal/mol, and that of the ~142° rotation from one gauche to its enantiomer is ~8 kcal/mol. The situation for butane is similar, but with sightly lower gauche energies and barriers. If the two parts of the molecule connected by a single bond are bulky or charged, the energy barriers may be much higher. For example, in
9048-462: The C − C {\displaystyle {\ce {C-C}}} axis. Thus, even if those angles and distances are assumed fixed, there are infinitely many conformations for the ethane molecule, that differ by the relative angle φ of rotation between the two groups. The feeble repulsion between the hydrogen atoms in the two methyl groups causes the energy to minimized for three specific values of φ, 120° apart. In those configurations,
9204-670: The Agency for Toxic Substances and Disease Registry (ATSDR) (2007), benzene is both a synthetically made and naturally occurring chemical from processes that include: volcanic eruptions, wild fires, synthesis of chemicals such as phenol , production of synthetic fibers , and fabrication of rubbers , lubricants , pesticides , medications, and dyes . The major sources of benzene exposure are tobacco smoke, automobile service stations, exhaust from motor vehicles, and industrial emissions; however, ingestion and dermal absorption of benzene can also occur through contact with contaminated water. Benzene
9360-534: The Boston metropolitan area caused hazardous conditions in multiple places, with the publication noting that the compound may eventually cause leukemia in some individuals. The word " benzene " derives from " gum benzoin " ( benzoin resin ), an aromatic resin known since ancient times in Southeast Asia, and later to European pharmacists and perfumers in the 16th century via trade routes. An acidic material
9516-674: The Earth's crust and be subjected to conditions which allow it to slowly transform into fossil fuels like petroleum. The latter happened through catagenesis in which the reactions were mostly radical rearrangements of kerogen. These reactions took thousands to millions of years and no external reactants were involved. Due to the radical nature of these reactions, kerogen reacted towards two classes of products: those with low H/C ratio ( anthracene or products similar to it) and those with high H/C ratio ( methane or products similar to it); i.e., carbon-rich or hydrogen-rich products. Because catagenesis
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#17327808341229672-490: The Orinoco Belt . While significant volumes of oil are extracted from oil sands, particularly in Canada, logistical and technical hurdles remain, as oil extraction requires large amounts of heat and water, making its net energy content quite low relative to conventional crude oil. Thus, Canada's oil sands are not expected to provide more than a few million barrels per day in the foreseeable future. Petroleum consists of
9828-808: The Soviet Union in total output. In 1973 , Saudi Arabia and other Arab nations imposed an oil embargo against the United States, United Kingdom, Japan and other Western nations which supported Israel in the Yom Kippur War of October 1973. The embargo caused an oil crisis . This was followed by the 1979 oil crisis , which was caused by a drop in oil production in the wake of the Iranian Revolution and caused oil prices to more than double. The two oil price shocks had many short- and long-term effects on global politics and
9984-478: The United States , but is responsible for only one percent of electricity generation. Petroleum's worth as a portable, dense energy source powering the vast majority of vehicles and as the base of many industrial chemicals makes it one of the world's most important commodities . The top three oil-producing countries as of 2018 are the United States, Russia , and Saudi Arabia . In 2018, due in part to developments in hydraulic fracturing and horizontal drilling ,
10140-455: The actinomycetales order of bacteria also produced antibiotic compounds (e.g., streptomycin ). Thus the action of anaerobic bacteria ceased at about 10 m below the water or sediment. The mixture at this depth contained fulvic acids, unreacted and partially reacted fats and waxes, slightly modified lignin , resins and other hydrocarbons. As more layers of organic matter settled into the sea or lake bed, intense heat and pressure built up in
10296-479: The cis and trans labels are ambiguous. The IUPAC recommends a more precise labeling scheme, based on the CIP priorities for the bonds at each carbon atom. More generally, atoms or atom groups that can form three or more non-equivalent single bonds (such as the transition metals in coordination compounds) may give rise to multiple stereoisomers when different atoms or groups are attached at those positions. The same
10452-585: The 12th century. It has also been present in Romania since the 13th century, being recorded as păcură. Sophisticated oil pits, 4.5 to 6 metres (15 to 20 ft) deep, were dug by the Seneca people and other Iroquois in Western Pennsylvania as early as 1415–1450. The French General Louis-Joseph de Montcalm encountered Seneca using petroleum for ceremonial fires and as a healing lotion during
10608-503: The American Association of Petroleum Geologists. "The controversy is over how much they contribute to Earth's overall reserves and how much time and effort geologists should devote to seeking them out." Three conditions must be present for oil reservoirs to form: The reactions that produce oil and natural gas are often modeled as first order breakdown reactions, where hydrocarbons are broken down to oil and natural gas by
10764-455: The Earth's surface. Unusual magma intrusions, however, could have created greater localized heating. Geologists often refer to the temperature range in which oil forms as an "oil window" . Below the minimum temperature oil remains trapped in the form of kerogen. Above the maximum temperature the oil is converted to natural gas through the process of thermal cracking . Sometimes, oil formed at extreme depths may migrate and become trapped at
10920-479: The REL (10-hour) of 0.1 ppm. The NIOSH short-term exposure limit (STEL – 15 min) is 1 ppm. American Conference of Governmental Industrial Hygienists (ACGIH) adopted Threshold Limit Values (TLVs) for benzene at 0.5 ppm TWA and 2.5 ppm STEL. Several tests can determine exposure to benzene. Benzene itself can be measured in breath, blood or urine, but such testing is usually limited to the first 24 hours post-exposure due to
11076-586: The Soviet Union included the goal to capture the Baku oilfields , as it would provide much-needed oil supplies for the German military which was suffering from blockades. Oil exploration in North America during the early 20th century later led to the U.S. becoming the leading producer by mid-century. As petroleum production in the U.S. peaked during the 1960s, the United States was surpassed by Saudi Arabia and
11232-576: The United States became the world's largest producer. About 80 percent of the world's readily accessible reserves are located in the Middle East , with 62.5 percent coming from the Arab five: Saudi Arabia , United Arab Emirates , Iraq , Qatar , and Kuwait . A large portion of the world's total oil exists as unconventional sources, such as bitumen in Athabasca oil sands and extra heavy oil in
11388-627: The air at a recorded rate of 480 cubic metres (3,000 bbl) per day. By the end of the 19th century the Russian Empire, particularly the Branobel company in Azerbaijan , had taken the lead in production. Access to oil was and still is a major factor in several military conflicts of the 20th century, including World War II , during which oil facilities were a major strategic asset and were extensively bombed . The German invasion of
11544-551: The area around modern Baku , Azerbaijan . These fields were described by the Persian geographer Abu Bakr al-Razi in the 10th century, and by Marco Polo in the 13th century, who described the output of those wells as hundreds of shiploads. Arab and Persian chemists also distilled crude oil to produce flammable products for military purposes. Through Islamic Spain , distillation became available in Western Europe by
11700-457: The atoms back to the original positions. Changing the shape of the molecule from such an energy minimum A {\displaystyle {\ce {A}}} to another energy minimum B {\displaystyle {\ce {B}}} will therefore require going through configurations that have higher energy than A {\displaystyle {\ce {A}}} and B {\displaystyle {\ce {B}}} . That is,
11856-495: The barriers between these are significantly lower than those between different cis - trans isomers). Cis and trans isomers also occur in inorganic coordination compounds , such as square planar MX 2 Y 2 {\displaystyle {\ce {MX2Y2}}} complexes and octahedral MX 4 Y 2 {\displaystyle {\ce {MX4Y2}}} complexes. For more complex organic molecules,
12012-479: The benzene content in gasoline to 0.62%. In some European languages, the word for petroleum or gasoline is an exact cognate of "benzene". For instance in Catalan the word 'benzina' can be used for gasoline, though now it is relatively rare. The most common reactions of benzene involve substitution of a proton by other groups. Electrophilic aromatic substitution is a general method of derivatizing benzene. Benzene
12168-441: The benzene framework. Sulfonation of benzene involves the use of oleum , a mixture of sulfuric acid with sulfur trioxide . Sulfonated benzene derivatives are useful detergents . In nitration , benzene reacts with nitronium ions (NO 2 ), which is a strong electrophile produced by combining sulfuric and nitric acids. Nitrobenzene is the precursor to aniline . Chlorination is achieved with chlorine to give chlorobenzene in
12324-628: The biggest consumer country of benzene was China, followed by the USA. Benzene production is currently expanding in the Middle East and in Africa, whereas production capacities in Western Europe and North America are stagnating. Toluene is now often used as a substitute for benzene, for instance as a fuel additive. The solvent-properties of the two are similar, but toluene is less toxic and has
12480-426: The carbons alternately above and below their mean plane) and boat (with two opposite carbons above the plane, and the other four below it). If the energy barrier between two conformational isomers is low enough, it may be overcome by the random inputs of thermal energy that the molecule gets from interactions with the environment or from its own vibrations . In that case, the two isomers may as well be considered
12636-460: The central atom M forms six bonds with octahedral geometry , has at least two facial–meridional isomers , depending on whether the three X {\displaystyle {\ce {X}}} bonds (and thus also the three Y {\displaystyle {\ce {Y}}} bonds) are directed at the three corners of one face of the octahedron ( fac isomer), or lie on the same equatorial or "meridian" plane of it ( mer isomer). Two parts of
12792-474: The coal industry dominated the petroleum technologies. Chemist James Young in 1847 noticed a natural petroleum seepage in the coal mine at riddings Alfreton , Derbyshire from which he distilled a light thin oil suitable for use as lamp oil, at the same time obtaining a more viscous oil suitable for lubricating machinery. In 1848, Young set up a small business refining crude oil. Young eventually succeeded, by distilling cannel coal at low heat, in creating
12948-460: The compound biphenyl – two phenyl groups connected by a single bond – the repulsion between hydrogen atoms closest to the central single bond gives the fully planar conformation, with the two rings on the same plane, a higher energy than conformations where the two rings are skewed. In the gas phase, the molecule has therefore at least two rotamers, with the ring planes twisted by ±47°, which are mirror images of each other. The barrier between them
13104-546: The compound the name benzin . In 1836, the French chemist Auguste Laurent named the substance "phène"; this word has become the root of the English word " phenol ", which is hydroxylated benzene, and " phenyl ", the radical formed by abstraction of a hydrogen atom from benzene. In 1845, Charles Blachford Mansfield , working under August Wilhelm von Hofmann , isolated benzene from coal tar . Four years later, Mansfield began
13260-433: The cyclohexane molecule with all six carbon atoms on the same plane have a higher energy, because some or all the C − C − C {\displaystyle {\ce {C-C-C}}} angles must be far from that value (120 degrees for a regular hexagon). Thus the conformations which are local energy minima have the ring twisted in space, according to one of two patterns known as chair (with
13416-573: The earliest Chinese writings, cites that oil in its raw state, without refining, was first discovered, extracted, and used in China in the first century BCE. In addition, the Chinese were the first to record the use of petroleum as fuel as early as the fourth century BCE. By 347 CE, oil was produced from bamboo-drilled wells in China. In the 7th century, petroleum was among the essential ingredients for Greek fire , an incendiary projectile weapon that
13572-426: The energy is at a local minimum. The corresponding conformations of the molecule are called rotational isomers or rotamers . Thus, for example, in an ethane molecule H 3 C − CH 3 {\displaystyle {\ce {H3C-CH3}}} , all the bond angles and length are narrowly constrained, except that the two methyl groups can independently rotate about
13728-469: The environment and human health. Extraction , refining and burning of petroleum fuels all release large quantities of greenhouse gases , so petroleum is one of the major contributors to climate change . Other negative environmental effects include direct releases, such as oil spills , as well as air and water pollution at almost all stages of use. These environmental effects have direct and indirect health consequences for humans. Oil has also been
13884-406: The equilibrium between neutral and zwitterionic forms of an amino acid . The structure of some molecules is sometimes described as a resonance between several apparently different structural isomers. The classical example is 1,2-dimethylbenzene ( o -xylene), which is often described as a mix of the two apparently distinct structural isomers: However, neither of these two structures describes
14040-399: The existence or possibility of isomers. Isomers do not necessarily share similar chemical or physical properties . Two main forms of isomerism are structural (or constitutional) isomerism, in which bonds between the atoms differ; and stereoisomerism or (spatial isomerism), in which the bonds are the same but the relative positions of the atoms differ. Isomeric relationships form
14196-425: The fact that it happened at relatively low temperatures (when compared to commercial pyrolysis plants) of 60 to several hundred °C. Pyrolysis was possible because of the long reaction times involved. Heat for catagenesis came from the decomposition of radioactive materials of the crust, especially K , Th , U and U . The heat varied with geothermal gradient and was typically 10–30 °C per km of depth from
14352-401: The first industrial-scale production of benzene, based on the coal-tar method. Gradually, the sense developed among chemists that a number of substances were chemically related to benzene, comprising a diverse chemical family. In 1855, Hofmann was the first to apply the word " aromatic " to designate this family relationship, after a characteristic property of many of its members. In 1997, benzene
14508-440: The fusion process is the hydrogen-free allotrope of carbon, graphite . In heterocycles , carbon atoms in the benzene ring are replaced with other elements. The most important variations contain nitrogen . Replacing one CH with N gives the compound pyridine , C 5 H 5 N. Although benzene and pyridine are structurally related, benzene cannot be converted into pyridine. Replacement of a second CH bond with N gives, depending on
14664-815: The global economy. They led to sustained reductions in demand as a result of substitution to other fuels, especially coal and nuclear, and improvements in energy efficiency , facilitated by government policies. High oil prices also induced investment in oil production by non-OPEC countries, including Prudhoe Bay in Alaska, the North Sea offshore fields of the United Kingdom and Norway, the Cantarell offshore field of Mexico, and oil sands in Canada. About 90 percent of vehicular fuel needs are met by oil. Petroleum also makes up 40 percent of total energy consumption in
14820-408: The heavier end of the range, paraffin wax is an alkane with approximately 25 carbon atoms, while asphalt has 35 and up, although these are usually cracked in modern refineries into more valuable products. The lightest fraction, the so-called petroleum gases are subjected to diverse processing depending on cost. These gases are either flared off , sold as liquefied petroleum gas , or used to power
14976-451: The human body. Exposure to benzene may lead progressively to aplastic anemia , leukaemia , and multiple myeloma . OSHA regulates levels of benzene in the workplace. The maximum allowable amount of benzene in workroom air during an 8-hour workday, 40-hour workweek is 1 ppm. As benzene can cause cancer , NIOSH recommends that all workers wear special breathing equipment when they are likely to be exposed to benzene at levels exceeding
15132-564: The hydrogen atom. In order to change one conformation to the other, at some point those four atoms would have to lie on the same plane – which would require severely straining or breaking their bonds to the carbon atom. The corresponding energy barrier between the two conformations is so high that there is practically no conversion between them at room temperature, and they can be regarded as different configurations. The compound chlorofluoromethane CH 2 ClF {\displaystyle {\ce {CH2ClF}}} , in contrast,
15288-462: The internal energy of a molecule, which is determined by the angles between bonds in each atom and by the distances between atoms (whether they are bonded or not). A conformational isomer is an arrangement of the atoms of the molecule or ion for which the internal energy is a local minimum ; that is, an arrangement such that any small changes in the positions of the atoms will increase the internal energy, and hence result in forces that tend to push
15444-658: The invention of the modern kerosene lamp (1853), the introduction of the first modern street lamp in Europe (1853), and the construction of the world's first modern oil "mine" (1854). at Bóbrka , near Krosno (still operational as of 2020). The demand for petroleum as a fuel for lighting in North America and around the world quickly grew. The first oil well in the Americas was drilled in 1859 by Edwin Drake at what
15600-446: The large number of co-eluted hydrocarbons within oil, many cannot be resolved by traditional gas chromatography. This unresolved complex mixture (UCM) of hydrocarbons is particularly apparent when analysing weathered oils and extracts from tissues of organisms exposed to oil. Crude oil varies greatly in appearance depending on its composition. It is usually black or dark brown (although it may be yellowish, reddish, or even greenish). In
15756-417: The late 1970s. Trace amounts of benzene are found in petroleum and coal. It is a byproduct of the incomplete combustion of many materials. For commercial use, until World War II , much of benzene was obtained as a by-product of coke production (or "coke-oven light oil") for the steel industry. However, in the 1950s, increased demand for benzene, especially from the growing polymers industry, necessitated
15912-532: The location of the second N, pyridazine , pyrimidine , or pyrazine . Four chemical processes contribute to industrial benzene production: catalytic reforming , toluene hydrodealkylation, toluene disproportionation, and steam cracking etc. According to the ATSDR Toxicological Profile for benzene, between 1978 and 1981, catalytic reformates accounted for approximately 44–50% of the total U.S. benzene production. In catalytic reforming,
16068-411: The lower regions. As a consequence, compounds of this mixture began to combine in poorly understood ways to kerogen . Combination happened in a similar fashion as phenol and formaldehyde molecules react to urea-formaldehyde resins, but kerogen formation occurred in a more complex manner due to a bigger variety of reactants. The total process of kerogen formation from the beginning of anaerobic decay
16224-899: The matter to H 2 S and N 2 respectively by using the matter as a source for other reactants. Due to such anaerobic bacteria, at first, this matter began to break apart mostly via hydrolysis : polysaccharides and proteins were hydrolyzed to simple sugars and amino acids respectively. These were further anaerobically oxidized at an accelerated rate by the enzymes of the bacteria: e.g., amino acids went through oxidative deamination to imino acids , which in turn reacted further to ammonia and α-keto acids . Monosaccharides in turn ultimately decayed to CO 2 and methane . The anaerobic decay products of amino acids, monosaccharides, phenols and aldehydes combined into fulvic acids . Fats and waxes were not extensively hydrolyzed under these mild conditions. Some phenolic compounds produced from previous reactions worked as bactericides and
16380-638: The middle carbon propan-2-ol (2-propanol, isopropyl alcohol, isopropanol; II ). These can be described by the condensed structural formulas H 3 C − CH 2 − CH 2 OH {\displaystyle {\ce {H3C-CH2-CH2OH}}} and H 3 C − CH ( OH ) − CH 3 {\displaystyle {\ce {H3C-CH(OH)-CH3}}} . The third isomer of C 3 H 8 O {\displaystyle {\ce {C3H8O}}}
16536-410: The molecular formula C 3 H 8 O {\displaystyle {\ce {C3H8O}}} : The first two isomers shown of C 3 H 8 O {\displaystyle {\ce {C3H8O}}} are propanols , that is, alcohols derived from propane . Both have a chain of three carbon atoms connected by single bonds, with
16692-585: The molecule 1,2-dichloroethane ( ClH 2 C − CH 2 Cl {\displaystyle {\ce {ClH2C-CH2Cl}}} also has three local energy minima, but they have different energies due to differences between the H − H {\displaystyle {\ce {H-H}}} , Cl − Cl {\displaystyle {\ce {Cl-Cl}}} , and H − Cl {\displaystyle {\ce {H-Cl}}} interactions. There are therefore three rotamers:
16848-410: The molecule, not just two different conformations. (However, one should be aware that the terms "conformation" and "configuration" are largely synonymous outside of chemistry, and their distinction may be controversial even among chemists. ) Interactions with other molecules of the same or different compounds (for example, through hydrogen bonds ) can significantly change the energy of conformations of
17004-407: The molecule. The German chemist Wilhelm Körner suggested the prefixes ortho-, meta-, para- to distinguish di-substituted benzene derivatives in 1867; however, he did not use the prefixes to distinguish the relative positions of the substituents on a benzene ring. It was the German chemist Carl Gräbe who, in 1869, first used the prefixes ortho-, meta-, para- to denote specific relative locations of
17160-586: The ortho, meta, and para patterns of arene substitution —to argue in support of his proposed structure. Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio. The new understanding of benzene, and hence of all aromatic compounds, proved to be so important for both pure and applied chemistry that in 1890 the German Chemical Society organized an elaborate appreciation in Kekulé's honor, celebrating
17316-408: The other ( propyne or methylacetylene; II ) they are connected by a single bond and a triple bond . In the third isomer ( cyclopropene ; III ) the three carbons are connected into a ring by two single bonds and a double bond. In all three, the remaining valences of the carbon atoms are satisfied by the four hydrogens. Again, note that there is only one structural isomer with a triple bond, because
17472-654: The other possible placement of that bond is just drawing the three carbons in a different order. For the same reason, there is only one cyclopropene, not three. Tautomers are structural isomers which readily interconvert, so that two or more species co-exist in equilibrium such as H − X − Y = Z ↽ − − ⇀ X = Y − Z − H {\displaystyle {\ce {H-X-Y=Z <=> X=Y-Z-H}}} . Important examples are keto-enol tautomerism and
17628-514: The other side of"), respectively; or Z and E in the IUPAC recommended nomenclature. Conversion between these two forms usually requires temporarily breaking bonds (or turning the double bond into a single bond), so the two are considered different configurations of the molecule. More generally, cis – trans isomerism (formerly called "geometric isomerism") occurs in molecules where the relative orientation of two distinguishable functional groups
17784-404: The parody was a lampoon of the snake anecdote, possibly already well known through oral transmission even if it had not yet appeared in print. Kekulé's 1890 speech in which this anecdote appeared has been translated into English. If the anecdote is the memory of a real event, circumstances mentioned in the story suggest that it must have happened early in 1862. In 1929, the cyclic nature of benzene
17940-819: The plane of polarized light that passes through it. The rotation has the same magnitude but opposite senses for the two isomers, and can be a useful way of distinguishing and measuring their concentration in a solution. For this reason, enantiomers were formerly called "optical isomers". However, this term is ambiguous and is discouraged by the IUPAC . Stereoisomers that are not enantiomers are called diastereomers . Some diastereomers may contain chiral center , some not. Some enantiomer pairs (such as those of trans -cyclooctene ) can be interconverted by internal motions that change bond lengths and angles only slightly. Other pairs (such as CHFClBr) cannot be interconverted without breaking bonds, and therefore are different configurations. A double bond between two carbon atoms forces
18096-485: The presence of a Lewis acid catalyst such as aluminium tri-chloride. Via hydrogenation , benzene and its derivatives convert to cyclohexane and derivatives. This reaction is achieved by the use of high pressures of hydrogen in the presence of heterogeneous catalysts , such as finely divided nickel . Whereas alkenes can be hydrogenated near room temperatures, benzene and related compounds are more reluctant substrates, requiring temperatures >100 °C. This reaction
18252-435: The presence of a strong Lewis acid catalyst. Similarly, the Friedel-Crafts acylation is a related example of electrophilic aromatic substitution . The reaction involves the acylation of benzene (or many other aromatic rings) with an acyl chloride using a strong Lewis acid catalyst such as aluminium chloride or Iron(III) chloride . Using electrophilic aromatic substitution, many functional groups are introduced onto
18408-423: The presence of chiral catalysts , such as most enzymes . For this latter reason, the two enantiomers of most chiral compounds usually have markedly different effects and roles in living organisms. In biochemistry and food science , the two enantiomers of a chiral molecule – such as glucose – are usually identified, and treated as very different substances. Each enantiomer of a chiral compound typically rotates
18564-484: The prevention of adverse effects, is zero benzene concentration in drinking water. The EPA requires that spills or accidental releases into the environment of 10 pounds (4.5 kg) or more of benzene be reported. The U.S. Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit of 1 part of benzene per million parts of air (1 ppm) in the workplace during an 8-hour workday, 40-hour workweek. The short term exposure limit for airborne benzene
18720-612: The problem of how carbon atoms could bond to up to four other atoms at the same time. Curiously, a similar, humorous depiction of benzene had appeared in 1886 in a pamphlet entitled Berichte der Durstigen Chemischen Gesellschaft (Journal of the Thirsty Chemical Society), a parody of the Berichte der Deutschen Chemischen Gesellschaft , only the parody had monkeys seizing each other in a circle, rather than snakes as in Kekulé's anecdote. Some historians have suggested that
18876-445: The production of benzene from petroleum. Today, most benzene comes from the petrochemical industry , with only a small fraction being produced from coal. Benzene has been detected on Mars . X-ray diffraction shows that all six carbon-carbon bonds in benzene are of the same length, at 140 picometres (pm). The C–C bond lengths are greater than a double bond (135 pm) but shorter than a single bond (147 pm). This intermediate distance
19032-556: The proportion of chemical elements varies over fairly narrow limits as follows: Four different types of hydrocarbon appear in crude oil. The relative percentage of each varies from oil to oil, determining the properties of each oil. The alkanes from pentane (C 5 H 12 ) to octane (C 8 H 18 ) are refined into gasoline, the ones from nonane (C 9 H 20 ) to hexadecane (C 16 H 34 ) into diesel fuel , kerosene and jet fuel . Alkanes with more than 16 carbon atoms can be refined into fuel oil and lubricating oil . At
19188-556: The reaction mixture (or reformate) by extraction with any one of a number of solvents , including diethylene glycol or sulfolane , and benzene is then separated from the other aromatics by distillation. The extraction step of aromatics from the reformate is designed to produce aromatics with lowest non-aromatic components. Recovery of the aromatics, commonly referred to as BTX (benzene, toluene and xylene isomers), involves such extraction and distillation steps. In similar fashion to this catalytic reforming, UOP and BP commercialized
19344-465: The recommended (8-hour) exposure limit of 0.1 ppm. The United States Environmental Protection Agency has set a maximum contaminant level for benzene in drinking water at 0.005 mg/L (5 ppb), as promulgated via the U.S. National Primary Drinking Water Regulations. This regulation is based on preventing benzene leukemogenesis . The maximum contaminant level goal ( MCLG ), a nonenforceable health goal that would allow an adequate margin of safety for
19500-644: The refinery's own burners. During the winter, butane (C 4 H 10 ), is blended into the gasoline pool at high rates, because its high vapour pressure assists with cold starts. The aromatic hydrocarbons are unsaturated hydrocarbons that have one or more benzene rings . They tend to burn with a sooty flame, and many have a sweet aroma. Some are carcinogenic . These different components are separated by fractional distillation at an oil refinery to produce gasoline, jet fuel, kerosene, and other hydrocarbon fractions. The components in an oil sample can be determined by gas chromatography and mass spectrometry . Due to
19656-519: The relatively rapid removal of the chemical by exhalation or biotransformation. Most people in developed countries have measureable baseline levels of benzene and other aromatic petroleum hydrocarbons in their blood. In the body, benzene is enzymatically converted to a series of oxidation products including muconic acid , phenylmercapturic acid , phenol , catechol , hydroquinone and 1,2,4-trihydroxybenzene . Most of these metabolites have some value as biomarkers of human exposure, since they accumulate in
19812-411: The remaining carbon valences being filled by seven hydrogen atoms and by a hydroxyl group − OH {\displaystyle {\ce {-OH}}} comprising the oxygen atom bound to a hydrogen atom. These two isomers differ on which carbon the hydroxyl is bound to: either to an extremity of the carbon chain propan-1-ol (1-propanol, n -propyl alcohol, n -propanol; I ) or to
19968-529: The remaining four bonds (if they are single) to lie on the same plane, perpendicular to the plane of the bond as defined by its π orbital . If the two bonds on each carbon connect to different atoms, two distinct conformations are possible, that differ from each other by a twist of 180 degrees of one of the carbons about the double bond. The classical example is dichloroethene C 2 H 2 Cl 2 {\displaystyle {\ce {C2H2Cl2}}} , specifically
20124-412: The reservoir it is usually found in association with natural gas, which being lighter forms a "gas cap" over the petroleum, and saline water which, being heavier than most forms of crude oil, generally sinks beneath it. Crude oil may also be found in a semi-solid form mixed with sand and water, as in the Athabasca oil sands in Canada, where it is usually referred to as crude bitumen . In Canada, bitumen
20280-476: The ring, and the unstable product is immediately reduced (by NADH ) to a cyclic diol with two double bonds, breaking the aromaticity. Next, the diol is newly reduced by NADH to catechol . The catechol is then metabolized to acetyl CoA and succinyl CoA , used by organisms mainly in the citric acid cycle for energy production. Petroleum Petroleum is a naturally occurring yellowish-black liquid mixture. It consists mainly of hydrocarbons , and
20436-518: The same time the world's first, small, oil refinery was opened at Jasło in Poland (then Austria), with a larger one opened at Ploiești in Romania shortly after. Romania (then being a vassal of the Ottoman empire) is the first country in the world to have had its annual crude oil output officially recorded in international statistics: 275 tonnes for 1857. In 1858, Georg Christian Konrad Hunäus found
20592-409: The same type, but differ in their shapes – the relative positions of those atoms in space – apart from rotations and translations . In theory, one can imagine any arrangement in space of the atoms of a molecule or ion to be gradually changed to any other arrangement in infinitely many ways, by moving each atom along an appropriate path. However, changes in the positions of atoms will generally change
20748-502: The sandwich and half-sandwich complexes, respectively, Cr(C 6 H 6 ) 2 and [RuCl 2 (C 6 H 6 )] 2 . Benzene is classified as a carcinogen , which increases the risk of cancer and other illnesses, and is also a notorious cause of bone marrow failure . Substantial quantities of epidemiologic, clinical, and laboratory data link benzene to aplastic anemia, acute leukemia , bone marrow abnormalities and cardiovascular disease. The specific hematologic malignancies that benzene
20904-523: The second half of the 19th century, the term became commonly known for the liquid form of hydrocarbons. Petroleum, in one form or another, has been used since ancient times. More than 4300 years ago, bitumen was mentioned when the Sumerians used it to make boats. A tablet of the legend of the birth of Sargon of Akkad mentions a basket which was closed by straw and bitumen. More than 4000 years ago, according to Herodotus and Diodorus Siculus , asphalt
21060-406: The six planes H − C − C {\displaystyle {\ce {H-C-C}}} or C − C − H {\displaystyle {\ce {C-C-H}}} are 60° apart. Discounting rotations of the whole molecule, that configuration is a single isomer – the so-called staggered conformation. Rotation between the two halves of
21216-412: The structural isomer Cl − HC = CH − Cl {\displaystyle {\ce {Cl-HC=CH-Cl}}} that has one chlorine bonded to each carbon. It has two conformational isomers, with the two chlorines on the same side or on opposite sides of the double bond's plane. They are traditionally called cis (from Latin meaning "on this side of") and trans ("on
21372-686: The substituents on a di-substituted aromatic ring (viz, naphthalene). In 1870, the German chemist Viktor Meyer first applied Gräbe's nomenclature to benzene. In 1903, Ludwig Roselius popularized the use of benzene to decaffeinate coffee . This discovery led to the production of Sanka . This process was later discontinued. Benzene was historically used as a significant component in many consumer products such as liquid wrench , several paint strippers , rubber cements , spot removers, and other products. Manufacture of some of these benzene-containing formulations ceased in about 1950, although Liquid Wrench continued to contain significant amounts of benzene until
21528-408: The term stems from monasteries in southern Italy where it was in use by the end of the first millennium as an alternative for the older term " naphtha ". After that, the term was used in numerous manuscripts and books, such as in the treatise De Natura Fossilium , published in 1546 by the German mineralogist Georg Bauer , also known as Georgius Agricola. After the advent of the oil industry, during
21684-460: The three middle carbons are in a straight line, while the first three and last three lie on perpendicular planes. The molecule and its mirror image are not superimposable, even though the molecule has an axis of symmetry. The two enantiomers can be distinguished, for example, by the right-hand rule . This type of isomerism is called axial isomerism . Enantiomers behave identically in chemical reactions, except when reacted with chiral compounds or in
21840-539: The title of E.W. Binney & Co. at Bathgate in West Lothian and E. Meldrum & Co. at Glasgow; their works at Bathgate were completed in 1851 and became the first truly commercial oil-works in the world with the first modern oil refinery. The world's first oil refinery was built in 1856 by Ignacy Łukasiewicz in Austria. His achievements also included the discovery of how to distill kerosene from seep oil,
21996-433: The twenty-fifth anniversary of his first benzene paper. Here Kekulé spoke of the creation of the theory. He said that he had discovered the ring shape of the benzene molecule after having a reverie or day-dream of a snake biting its own tail (a symbol in ancient cultures known as the ouroboros ). This vision, he said, came to him after years of studying the nature of carbon-carbon bonds. This was seven years after he had solved
22152-448: The two "axial" positions, or one of the three "equatorial" positions. For the compound PF 3 Cl 2 {\displaystyle {\ce {PF3Cl2}}} , three isomers are possible, with zero, one, or two chlorines in the axial positions. As another example, a complex with a formula like MX 3 Y 3 {\displaystyle {\ce {MX3Y3}}} , where
22308-484: The two conformations with minimum energy interconvert in a few picoseconds even at very low temperatures. Conversely, the energy barrier may be so high that the easiest way to overcome it would require temporarily breaking and then reforming one or more bonds of the molecule. In that case, the two isomers usually are stable enough to be isolated and treated as distinct substances. These isomers are then said to be different configurational isomers or "configurations" of
22464-504: The urine in proportion to the extent and duration of exposure, and they may still be present for some days after exposure has ceased. The current ACGIH biological exposure limits for occupational exposure are 500 μg/g creatinine for muconic acid and 25 μg/g creatinine for phenylmercapturic acid in an end-of-shift urine specimen. Even if it is not a common substrate for metabolism, benzene can be oxidized by both bacteria and eukaryotes . In bacteria, dioxygenase enzyme can add an oxygen to
22620-468: The volume of the world's reserves of conventional oil. Petroleum is a fossil fuel derived from fossilized organic materials , such as zooplankton and algae . Vast amounts of these remains settled to sea or lake bottoms where they were covered in stagnant water (water with no dissolved oxygen ) or sediments such as mud and silt faster than they could decompose aerobically . Approximately 1 m below this sediment, water oxygen concentration
22776-702: The workplace. The U.S. National Institute for Occupational Safety and Health (NIOSH) revised the Immediately Dangerous to Life and Health (IDLH) concentration for benzene to 500 ppm. The current NIOSH definition for an IDLH condition, as given in the NIOSH Respirator Selection Logic, is one that poses a threat of exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent adverse health effects or prevent escape from such an environment. The purpose of establishing an IDLH value
22932-470: The xylene stream exiting the TDP unit is approximately 90% p -xylene. In some systems, even the benzene-to-xylenes ratio is modified to favor xylenes. Steam cracking is the process for producing ethylene and other alkenes from aliphatic hydrocarbons . Depending on the feedstock used to produce the olefins, steam cracking can produce a benzene-rich liquid by-product called pyrolysis gasoline . Pyrolysis gasoline can be blended with other hydrocarbons as
23088-684: Was detected in deep space . The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Johann Josef Loschmidt in 1861 suggested possible structures that contained multiple double bonds or multiple rings, but in these years very little was known about aromatic chemistry, and so chemists were unable to adduce appropriate evidence to favor any particular formula. But many chemists had begun to work on aromatic substances, especially in Germany, and relevant data
23244-634: Was activity in various parts of the world in the mid-19th century. A group directed by Major Alexeyev of the Bakinskii Corps of Mining Engineers hand-drilled a well in the Baku region of Bibi-Heybat in 1846. There were engine-drilled wells in West Virginia in the same year as Drake's well. An early commercial well was hand dug in Poland in 1853, and another in nearby Romania in 1857. At around
23400-414: Was closed off from external reactants, the resulting composition of the fuel mixture was dependent on the composition of the kerogen via reaction stoichiometry . Three types of kerogen exist: type I (algal), II (liptinic) and III (humic), which were formed mainly from algae , plankton and woody plants (this term includes trees , shrubs and lianas ) respectively. Catagenesis was pyrolytic despite
23556-693: Was coming fast. In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject. Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to
23712-480: Was derived from benzoin by sublimation , and named "flowers of benzoin", or benzoic acid. The hydrocarbon derived from benzoic acid thus acquired the name benzin, benzol, or benzene. Michael Faraday first isolated and identified benzene in 1825 from the oily residue derived from the production of illuminating gas, giving it the name bicarburet of hydrogen . In 1833, Eilhard Mitscherlich produced it by distilling benzoic acid (from gum benzoin ) and lime . He gave
23868-446: Was finally confirmed by the crystallographer Kathleen Lonsdale using X-ray diffraction methods. Using large crystals of hexamethylbenzene , a benzene derivative with the same core of six carbon atoms, Lonsdale obtained diffraction patterns. Through calculating more than thirty parameters, Lonsdale demonstrated that the benzene ring could not be anything but a flat hexagon, and provided accurate distances for all carbon-carbon bonds in
24024-423: Was low, below 0.1 mg/L, and anoxic conditions existed. Temperatures also remained constant. As further layers settled into the sea or lake bed, intense heat and pressure built up in the lower regions. This process caused the organic matter to change, first into a waxy material known as kerogen , found in various oil shales around the world, and then with more heat into liquid and gaseous hydrocarbons via
24180-479: Was used by Byzantine Greeks against Arab ships, which were then attacking Constantinople . Crude oil was also distilled by Persian chemists , with clear descriptions given in Arabic handbooks such as those of Abu Bakr al-Razi (Rhazes). The streets of Baghdad were paved with tar , derived from petroleum that became accessible from natural fields in the region. In the 9th century, oil fields were exploited in
24336-544: Was used in the construction of the walls and towers of Babylon ; there were oil pits near Ardericca and Babylon, and a pitch spring on Zakynthos . Great quantities of it were found on the banks of the river Issus , one of the tributaries of the Euphrates . Ancient Persian tablets indicate the medicinal and lighting uses of petroleum in the upper levels of their society. The use of petroleum in ancient China dates back to more than 2000 years ago. The I Ching , one of
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