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| Names | |||
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| Preferred IUPAC name Buta-1,3-diene[1] | |||
Other names
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| Identifiers | |||
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3D model (JSmol) | |||
| 605258 | |||
| ChEBI | |||
| ChEMBL | |||
| ChemSpider |
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| ECHA InfoCard | 100.003.138 | ||
| EC Number |
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| 25198 | |||
| KEGG |
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| RTECS number |
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| UNII | |||
| UN number | 1010 | ||
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| Properties[4] | |||
| C4H6 CH2=CH-CH=CH2 | |||
| Molar mass | 54.0916 g/mol | ||
| Appearance | Colourless gas or refrigerated liquid | ||
| Odor | Mildly aromatic or gasoline-like | ||
| Density |
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| Melting point | −108.91 °C (−164.04 °F; 164.24 K) | ||
| Boiling point | −4.41 °C (24.06 °F; 268.74 K) | ||
| 1.3 g/L at 5 °C, 735 mg/L at 20 °C | |||
| Solubility | |||
| Vapor pressure | 2.4 atm (20 °C)[3] | ||
Refractive index (nD) | 1.4292 | ||
| Viscosity | 0.25 cP at 0 °C | ||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards | Flammable, irritative,carcinogen | ||
| GHS labelling:[7] | |||
  | |||
| Danger | |||
| H220,H340,H350 | |||
| P202,P210,P280,P308+P313,P377,P381,P403 | |||
| NFPA 704 (fire diamond) | |||
| Flash point | −85 °C (−121 °F; 188 K) liquid flash point[3] | ||
| 414 °C (777 °F; 687 K)[6] | |||
| Explosive limits | 2–12% | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose) | 548 mg/kg (rat, oral) | ||
LC50 (median concentration) | |||
LCLo (lowest published) | 250,000 ppm (rabbit, 30 min)[5] | ||
| NIOSH (US health exposure limits): | |||
PEL (Permissible) | TWA 1 ppm ST 5 ppm[3] | ||
REL (Recommended) | Potential occupational carcinogen[3] | ||
IDLH (Immediate danger) | 2000 ppm[3] | ||
| Safety data sheet (SDS) | ECSC 0017 | ||
| Related compounds | |||
| Isoprene Chloroprene | |||
Related compounds | Butane | ||
Except where otherwise noted, data are given for materials in theirstandard state (at 25 °C [77 °F], 100 kPa). | |||
1,3-Butadiene (/ˌbjuːtəˈdaɪiːn/ ⓘ)[8] is anorganic compound with the formula CH2=CH-CH=CH2. It is a colorless gas that is easily condensed to a liquid. It is important industrially as a precursor tosynthetic rubber.[9] The molecule can be viewed as the union of twovinyl groups. It is the simplestconjugated diene.
Although butadienebreaks down quickly in the atmosphere, it is nevertheless found in ambient air in urban and suburban areas as a consequence of its constantemission frommotor vehicles.[10]
The name butadiene can also refer to theisomer,1,2-butadiene, which is acumulated diene with structure H2C=C=CH−CH3. Thisallene has no industrial significance.
In 1863, French chemist E. Caventou isolated butadiene from thepyrolysis ofamyl alcohol.[11] Thishydrocarbon was identified as butadiene in 1886, afterHenry Edward Armstrong isolated it from among the pyrolysis products of petroleum.[12] In 1910, the Russian chemistSergei Lebedev polymerized butadiene and obtained a material with rubber-like properties. This polymer was, however, found to be too soft to replacenatural rubber in many applications, notably automobile tires.
The butadiene industry originated in the years beforeWorld War II. Many of the belligerent nations realized that in the event of war, they could be cut off from rubber plantations controlled by theBritish Empire, and sought to reduce their dependence on natural rubber.[13] In 1929,Eduard Tschunker andWalter Bock, working forIG Farben in Germany, made a copolymer ofstyrene and butadiene that could be used in automobile tires. Worldwide production quickly ensued, with butadiene being produced fromgrain alcohol in the Soviet Union and the United States, and from coal-derivedacetylene in Germany.
In 2020, 14.2 million tons were estimated to have been produced.[14]
In the United States, western Europe, and Japan, butadiene is produced as a byproduct of thesteam cracking process used to produceethylene and otheralkenes. When mixed with steam and briefly heated to very high temperatures (often over 900 °C), aliphatic hydrocarbons give up hydrogen to produce a complex mixture of unsaturated hydrocarbons, including butadiene. The quantity of butadiene produced depends on the hydrocarbons used as feed. Light feeds, such asethane, give primarilyethylene when cracked, but heavier feeds favor the formation of heavier olefins, butadiene, andaromatic hydrocarbons.
Butadiene is typically isolated from the other four-carbonhydrocarbons produced in steam cracking byextractive distillation using apolar aprotic solvent such asacetonitrile,N-methyl-2-pyrrolidone,furfural, ordimethylformamide, from which it is then stripped bydistillation.[15]
Butadiene can also be produced by the catalyticdehydrogenation of normalbutane (n-butane). The first such post-war commercial plant, producing 65,000tons per year of butadiene, began operations in 1957 inHouston, Texas.[16] Prior to that, in the 1940s theRubber Reserve Company, a part of the United States government, constructed several plants inBorger, Texas,Toledo, Ohio, andEl Segundo, California, to produce synthetic rubber for the war effort as part of the United States Synthetic Rubber Program.[17] Total capacity was 68 KMTA (Kilo Metric Tons per Annum).
Today, butadiene fromn-butane is commercially produced using the Houdry Catadiene process, which was developed during World War II. This entails treating butane overalumina andchromia at high temperatures.[18]
In other parts of the world, including South America, Eastern Europe, China, and India, butadiene is also produced fromethanol. While not competitive with steam cracking for producing large volumes of butadiene, lower capital costs make production from ethanol a viable option for smaller-capacity plants. Two processes were in use.
In the single-step process developed bySergei Lebedev, ethanol is converted to butadiene, hydrogen, and water at 400–450 °C over any of a variety of metal oxide catalysts:[19]
This process was the basis for theSoviet Union's synthetic rubber industry during and after World War II, and it remained in limited use in Russia and other parts of eastern Europe until the end of the 1970s. At the same time this type of manufacture was canceled in Brazil. As of 2017, no butadiene was produced industrially from ethanol.
In the other, two-step process, developed by the Russian emigre chemistIvan Ostromislensky, ethanol isoxidized toacetaldehyde, which reacts with additional ethanol over atantalum-promoted poroussilica catalyst at 325–350 °C to yield butadiene:[19]
This process was one of the three used in the United States to produce "government rubber" during World War II, although it is less economical than the butane or butene routes for the large volumes. Still, three plants with a total capacity of 200,000 tons per year were constructed in the U.S. (Institute, West Virginia,Louisville, Kentucky, andKobuta, Pennsylvania) with start-ups completed in 1943, the Louisville plant initially created butadiene from acetylene generated by an associatedcalcium carbide plant. The process remains in use today in China and India.
1,3-Butadiene can also be produced bycatalyticdehydrogenation of normalbutenes. This method was also used by theU.S. Synthetic Rubber Program (USSRP) during World War II. The process was much more economical than the alcohol or n-butane route but competed withaviation gasoline for available butene molecules (butenes were plentiful thanks tocatalytic cracking). The USSRP constructed several plants inBaton Rouge andLake Charles, Louisiana; Houston,Baytown, andPort Neches, Texas; andTorrance, California.[17] Total annual production was 275 KMTA.
In the 1960s, aHouston company known as "Petro-Tex" patented a process to produce butadiene from normalbutenes by oxidativedehydrogenation using a proprietary catalyst. It is unclear if this technology is practiced commercially.[20]
After World War II, the production from butenes became the major type of production in USSR.
1,3-Butadiene is inconvenient for laboratory use because it is gas. Laboratory procedures have been optimized for its generation from nongaseous precursors. It can be produced by the retro-Diels-Alder reaction ofcyclohexene.[21]Sulfolene is a convenient solid storable source for 1,3-butadiene in the laboratory. It releases the diene andsulfur dioxide upon heating.
Most butadiene (75% of the manufactured 1,3-butadiene[9]) is used to make synthetic rubbers for the manufacture of tires and components of many consumer items.
The conversion of butadiene to synthetic rubbers is calledpolymerization, a process by which small molecules (monomers) are linked to make large ones (polymers). The mere polymerization of butadiene givespolybutadiene, which is a very soft, almost liquid material. The polymerization of butadieneand othermonomers givescopolymers, which are more valued. The polymerization of butadiene andstyrene and/oracrylonitrile, such asacrylonitrile butadiene styrene (ABS),nitrile-butadiene (NBR), andstyrene-butadiene (SBR). These copolymers are tough and/or elastic depending on the ratio of the monomers used in their preparation. SBR is the material most commonly used for the production of automobile tires. Precursors to still other synthetic rubbers are prepared from butadiene. One ischloroprene.[18]
Smaller amounts of butadiene are used to makeadiponitrile, a precursor to somenylons. The conversion of butadiene to adiponitrile entails the addition ofhydrogen cyanide to each of the double bonds in butadiene. The process is calledhydrocyanation.
Butadiene is used to make the solventsulfolane.
Butadiene is also useful in the synthesis ofcycloalkanes andcycloalkenes, as it reacts with double and triple carbon-carbon bonds through Diels-Alder reactions. The most widely used such reactions involve reactions of butadiene with one or two other molecules of butadiene, i.e., dimerization and trimerization respectively. Via dimerization butadiene is converted to4-vinylcyclohexene andcyclooctadiene. In fact, vinylcyclohexene is a common impurity that accumulates when butadiene is stored. Via trimerization, butadiene is converted tocyclododecatriene. Some of these processes employnickel- ortitanium-containing catalysts.[22]
Butadiene is also a precursor to1-octene viapalladium-catalyzedtelomerization withmethanol. This reaction produces 1-methoxy-2,7-octadiene as an intermediate.[14]
The most stableconformer of 1,3-butadiene is thes-trans conformation, in which the molecule is planar, with the two pairs of double bonds facing opposite directions. This conformation is most stable becauseorbital overlap between double bonds is maximized, allowing for maximum conjugation, whilesteric effects are minimized. Conventionally, thes-trans conformation is considered to have a C2-C3dihedral angle of 180°. In contrast, thes-cis conformation, in which the dihedral angle is 0°, with the pair of double bonds facing the same direction is approximately 16.5 kJ/mol (3.9 kcal/mol) higher in energy, due to steric hindrance. This geometry is a local energy maximum, so in contrast to thes-trans geometry, it is not a conformer. Thegauche geometry, in which the double bonds of thes-cis geometry are twisted to give a dihedral angle of around 38°, is a second conformer that is around 12.0 kJ/mol (2.9 kcal/mol) higher in energy than thes-trans conformer. Overall, there is a barrier of 24.8 kJ/mol (5.9 kcal/mol) for isomerization between the two conformers.[23] This increased rotational barrier and strong overall preference for a near-planar geometry is evidence for a delocalized π system and a small degree of partial double bond character in the C–C single bond, in accord withresonance theory.
Despite the high energy of thes-cis conformation, 1,3-butadiene needs to assume this conformation (or one very similar) before it can participate as the four-electron component in concerted cycloaddition reactions like the Diels-Alder reaction.
Similarly, a combined experimental and computational study has found that the double bond ofs-trans-butadiene has a length of 133.8 pm, while that for ethylene has a length of 133.0 pm. This was taken as evidence of aπ-bond weakened and lengthened by delocalization, as depicted by the resonance structures shown below.[24]
A qualitative picture of themolecular orbitals of 1,3-butadiene is readily obtained by applying Hückel theory. (The article onHückel theory gives a derivation for the butadiene orbitals.)
1,3-Butadiene is also thermodynamically stabilized. While a monosubstituted double bond releases about 30.3 kcal/mol of heat upon hydrogenation, 1,3-butadiene releases slightly less (57.1 kcal/mol) than twice this energy (60.6 kcal/mol), expected for two isolated double bonds. That implies a stabilization energy of 3.5 kcal/mol.[25] Similarly, the hydrogenation of the terminal double bond of 1,4-pentadiene releases 30.1 kcal/mol of heat, while hydrogenation of the terminal double bond of conjugated (E)-1,3-pentadiene releases only 26.5 kcal/mol, implying a very similar value of 3.6 kcal/mol for the stabilization energy.[26] The ~3.5 kcal/mol difference in these heats of hydrogenation can be taken to be the resonance energy of a conjugated diene.
iron-tricarbonyl-3D-balls.png)
The industrial uses illustrate the tendency of butadiene to polymerize. Its susceptibility to 1,4-addition reactions is illustrated by its hydrocyanation. Like many dienes, it undergoes Pd-catalyzed reactions that proceed via allyl complexes.[28] It is a partner in Diels–Alder reactions, e.g. withmaleic anhydride to givetetrahydrophthalic anhydride.[29]
Like other dienes, butadiene is a ligand for low-valent metal complexes, e.g. the derivatives Fe(butadiene)(CO)3 and Mo(butadiene)3.
Butadiene is of low acute toxicity.LC50 is 12.5–11.5 vol% for inhalation by rats and mice.[18]
Long-term exposure has been associated withcardiovascular disease. There is a consistent association withleukemia, as well as a significant association with other cancers.[30]
IARC has designated 1,3-butadiene as aGroup 1carcinogen ('carcinogenic to humans'),[31] and theAgency for Toxic Substances Disease Registry and theUS EPA also list the chemical as a carcinogen.[32][33] TheAmerican Conference of Governmental Industrial Hygienists (ACGIH) lists the chemical as a suspected carcinogen.[33] TheNatural Resources Defense Council (NRDC) lists somedisease clusters that are suspected to be associated with this chemical.[34] Some researchers have concluded it is the most potent carcinogen incigarette smoke, twice as potent as the runner upacrylonitrile[35]
1,3-Butadiene is also a suspected humanteratogen.[36][37][38] Prolonged and excessive exposure can affect many areas in the human body; blood, brain, eye, heart, kidney, lung, nose and throat have all been shown to react to the presence of excessive 1,3-butadiene.[39] Animal data suggest that women have a higher sensitivity to possible carcinogenic effects of butadiene over men when exposed to the chemical. This may be due toestrogen receptor impacts. While these data reveal important implications to the risks of human exposure to butadiene, more data are necessary to draw conclusive risk assessments. There is also a lack of human data for the effects of butadiene on reproductive and development shown to occur in mice, but animal studies have shown breathing butadiene during pregnancy can increase the number of birth defects, and humans have the same hormone systems as animals.[40]
1,3-Butadiene is recognized as a highly reactivevolatile organic compound (HRVOC) for its potential to readily formozone, and as such, emissions of the chemical are highly regulated byTCEQ in parts of theHouston-Brazoria-GalvestonOzone Non-Attainment Area.[41]
| Properties | |
|---|---|
| Phase behavior | |
| Triple point | 164.2 K (-109.0 °C) ?bar |
| Critical point | 425 K (152 °C) 43.2bar |
| Structure | |
| Symmetry group | C2h |
| Gas properties | |
| ΔfH0 | 110.2 kJ/mol |
| Cp | 79.5 J/mol·K |
| Liquid properties | |
| ΔfH0 | 90.5 kJ/mol |
| S0 | 199.0 J/mol·K |
| Cp | 123.6 J/mol·K |
| Liquid density | 0.64 ×103 kg/m3 |
