Cyclohexane

{{Short description|Organic compound; 6-sided hydrocarbon ring}} {{chembox |Watchedfields = changed |verifiedrevid = 464366627 |Name=Cyclohexane |ImageFileL1 = Cyclohexane-2D-skeletal.svg |ImageNameL1 = Cyclohexane |ImageClassL1 = skin-invert |ImageFileR1 = Cyclohexane molecule chair spacefill.png |ImageClassR1 = bg-transparent |ImageNameR1 = 3D structure of a cyclohexane molecule |ImageFileL2 = Chair conformation of cyclohexane.svg |ImageNameL2 = Skeletal formula of cyclohexane in its chair conformation |ImageClassL2 = skin-invert |ImageFileR2 = Cyclohexane-chair-3D-balls.png |ImageClassR2 = bg-transparent |ImageNameR2 = Ball-and-stick model of cyclohexane in its chair conformation |PIN = Cyclohexane<ref name=iupac2013>{{cite book | title = Nomenclature of Organic Chemistry : IUPAC Recommendations and Preferred Names 2013 (Blue Book) | publisher = The Royal Society of Chemistry | date = 2014 | location = Cambridge | pages = P001–P004 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4| chapter = Front Matter }}</ref> |OtherNames = Hexanaphthene (archaic)<ref>{{cite web|url=http://www.dictionary.com/browse/hexanaphthene|title=Hexanaphthene|archive-url=https://web.archive.org/web/20180212201838/http://www.dictionary.com/browse/hexanaphthene|archive-date=2018-02-12|work=dictionary.com}}</ref> |Section1={{Chembox Identifiers |ChEBI_Ref = {{ebicite|correct|EBI}} |ChEBI = 29005 |DrugBank_Ref = {{drugbankcite|correct|drugbank}} |SMILES = C1CCCCC1 |ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |ChemSpiderID = 7787 |PubChem = 8078 |UNII_Ref = {{fdacite|correct|FDA}} |UNII = 48K5MKG32S |KEGG_Ref = {{keggcite|correct|kegg}} |KEGG = C11249 |InChI = 1/C6H12/c1-2-4-6-5-3-1/h1-6H2 |InChIKey = XDTMQSROBMDMFD-UHFFFAOYAZ |ChEMBL_Ref = {{ebicite|correct|EBI}} |ChEMBL = 15980 |DrugBank = DB03561 |Gmelin = 1662 |Beilstein = 1900225 |3DMet = B04304 |RTECS = GU6300000 |UNNumber = 1145 |StdInChI_Ref = {{stdinchicite|correct|chemspider}} |StdInChI = 1S/C6H12/c1-2-4-6-5-3-1/h1-6H2 |StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |StdInChIKey = XDTMQSROBMDMFD-UHFFFAOYSA-N |CASNo_Ref = {{cascite|correct|CAS}} |CASNo = 110-82-7 }} |Section2={{Chembox Properties |C=6|H=12 |Appearance = Colourless liquid |Odor = Sweet, gasoline-like |Density = 0.7739 g/ml (liquid); 0.996 g/ml (solid) |Solubility = Immiscible |SolubleOther = Soluble in ether, alcohol, acetone |MeltingPtC = 6.47 |BoilingPtC = 80.74 |Viscosity = 1.02 cP at 17 °C |RefractIndex = 1.42662 |VaporPressure = 78 mmHg (20 °C)<ref name=PGCH/> |MagSus = −68.13·10⁻⁶ cm³/mol }} |Section4={{Chembox Thermochemistry |DeltaHf = −156 kJ/mol |DeltaHc = −3920 kJ/mol }} |Section3={{Chembox Hazards |GHSPictograms = {{GHS flame}} {{GHS health hazard}} {{GHS exclamation mark}} {{GHS environment}} |GHSSignalWord = Danger |HPhrases = {{H-phrases|225|304|315|336}} |PPhrases = {{P-phrases|210|233|240|241|242|243|261|264|271|273|280|301+310|302+352|303+361+353|304+340|312|321|331|332+313|362|370+378|391|403+233|403+235|405|501}} |FlashPtC = -20 |AutoignitionPtC = 245 |NFPA-H = 1 |NFPA-F = 3 |NFPA-R = 0 |PEL = TWA 300 ppm (1050 mg/m³)<ref name=PGCH>{{PGCH|0163}}</ref> |ExploLimits = 1.3–8%<ref name=PGCH/> |IDLH = 1300 ppm<ref name=PGCH/> |REL = TWA 300 ppm (1050 mg/m³)<ref name=PGCH/> |LD50 = 12705 mg/kg (rat, oral)<br/>813 mg/kg (mouse, oral)<ref name=IDLH>{{IDLH|110827|Cyclohexane}}</ref> |LCLo = 17,142 ppm (mouse, 2&nbsp;h)<br/>26,600 ppm (rabbit, 1&nbsp;h)<ref name=IDLH/> }} |Section9={{Chembox Related |OtherFunction_label = cycloalkanes |OtherFunction = Cyclopentane<br />Cycloheptane |OtherCompounds = Cyclohexene<br />Benzene }} }}

'''Cyclohexane''' is a cycloalkane with the molecular formula {{chem2|'''C6H12'''|auto=1}}. Cyclohexane is non-polar. Cyclohexane is a colourless, flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products (in which it is sometimes used). Cyclohexane is mainly used for the industrial production of adipic acid and caprolactam, which are precursors to nylon.<ref name="Campbell2011">{{Cite book |last1=Campbell |first1=M. Larry |title=Ullmann's Encyclopedia of Industrial Chemistry |year=2011 |doi=10.1002/14356007.a08_209.pub2 |isbn=978-3527306732 |chapter=Cyclohexane}}</ref>

'''Cyclohexyl''' ('''{{chem2|C6H11}}''') is the alkyl substituent of cyclohexane and is abbreviated '''Cy'''.<ref>{{cite web |url=http://pubs.acs.org/paragonplus/submission/joceah/joceah_abbreviations.pdf |title=Standard Abbreviations and Acronyms |publisher=The Journal of Organic Chemistry |archive-url=https://web.archive.org/web/20180801004052/http://pubs.acs.org/paragonplus/submission/joceah/joceah_abbreviations.pdf |archive-date=1 Aug 2018}}</ref>

==Production== Cyclohexane is one of the components of naphtha, from which it can be extracted by advanced distillation methods. Distillation is usually combined with isomerization of methylcyclopentane, a similar component extracted from naphtha by similar methods. Together these processes cover only a minority (15-20%) of the modern industrial demand and are complemented by synthesis.<ref>{{Cite book |last=Weissermel |first=Klaus |url=https://books.google.com/books?id=AO5HyPl_X0wC&pg=PA345 |title=Industrial Organic Chemistry |last2=Arpe |first2=Hans-Jürgen |date=2008-07-11 |publisher=John Wiley & Sons |isbn=978-3-527-61459-2 |pages=345 |language=en}}</ref>

===Modern industrial synthesis=== On an industrial scale, cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel catalyst.{{Citation needed|date=October 2024}} Producers of cyclohexane account for approximately 11.4% of global demand for benzene.<ref>{{cite web|url=http://www.ceresana.com/en/market-studies/chemicals/benzene/|title=Benzene - Study: Market, Analysis, Trends 2021 - Ceresana|last=Ceresana|website=www.ceresana.com|access-date=4 May 2018|url-status=live|archive-url=https://web.archive.org/web/20171221002731/http://www.ceresana.com/en/market-studies/chemicals/benzene/|archive-date=21 December 2017}}</ref> The reaction is highly exothermic, with ΔH(500 K) = -216.37 kJ/mol. Dehydrogenation commenced noticeably above 300&nbsp;°C, reflecting the favorable entropy for dehydrogenation.<ref name=Ullmann/>

:300px|Catalytic hydrogenation of benzene to cyclohexane with a raney-nickel catalyst|class=skin-invert

===History of synthesis=== Unlike benzene, cyclohexane is not found in natural resources such as coal. For this reason, early investigators synthesized their cyclohexane samples.<ref>{{cite journal |title=The Curiously Intertwined Histories of Benzene and Cyclohexane |first=E. W. |last=Warnhoff |journal=J. Chem. Educ. |year=1996 |volume=73 |issue=6 |pages=494 |doi=10.1021/ed073p494 |bibcode=1996JChEd..73..494W}}</ref>

====Failure==== * In 1867 Marcellin Berthelot reduced benzene with hydroiodic acid at elevated temperatures.<ref>{{cite journal|last=Bertholet|year=1867|url=https://books.google.com/books?id=YVgSAAAAYAAJ&pg=PA53|title=Nouvelles applications des méthodes de réduction en chimie organique|trans-title=New applications of reduction methods in organic chemistry|journal=Bulletin de la Société Chimique de Paris|volume=series 2|issue=7|pages=53–65|language=fr}}</ref><ref>{{cite journal|last=Bertholet|year=1868|title=Méthode universelle pour réduire et saturer d'hydrogène les composés organiques|trans-title=Universal method for reducing and saturating organic compounds with hydrogen|journal=Bulletin de la Société Chimique de Paris|volume=series 2|issue=9|pages=8–31|url=https://books.google.com/books?id=r1sSAAAAYAAJ&q=Bertholet&pg=PA17|quote=En effet, la benzine, chauffée à 280° pendant 24 heures avec 80 fois son poids d'une solution aqueuse saturée à froid d'acide iodhydrique, se change à peu près entièrement en hydrure d'hexylène, C₁₂H₁₄, en fixant 4 fois son volume d'hydrogène: C₁₂H₆ + 4H₂ = C₁₂H₁₄ … Le nouveau carbure formé par la benzine est un corps unique et défini: il bout à 69°, et offre toutes les propriétés et la composition de l'hydrure d'hexylène extrait des pétroles.|trans-quote=In effect, benzene, heated to 280° for 24 hours with 80 times its weight of an aqueous solution of cold saturated hydroiodic acid, is changed almost entirely into hydride of hexylene, C₁₂H₁₄, [Note: this formula for hexane (C₆H₁₄) is wrong because chemists at that time used the incorrect atomic mass for carbon.] by fixing [i.e., combining with] 4 times its volume of hydrogen: C₁₂H₆ + 4H₂ = C₁₂H₁₄ The new carbon compound formed by benzene is a unique and well-defined substance: it boils at 69° and presents all the properties and the composition of hydride of hexylene extracted from oil.)|language=fr}}</ref> * In 1870, Adolf von Baeyer repeated the reaction<ref>{{cite journal|author=Adolf Baeyer|year=1870|url=https://books.google.com/books?id=RJU8AAAAIAAJ&pg=PA266|title=Ueber die Reduction aromatischer Kohlenwasserstoffe durch Jodphosphonium|trans-title=On the reduction of aromatic compound by phosphonium iodide [H₄IP]|journal=Annalen der Chemie und Pharmacie|volume=55|pages=266–281|quote=Bei der Reduction mit Natriumamalgam oder Jodphosphonium addiren sich im höchsten Falle sechs Atome Wasserstoff, und es entstehen Abkömmlinge, die sich von einem Kohlenwasserstoff C₆H₁₂ ableiten. Dieser Kohlenwasserstoff ist aller Wahrscheinlichkeit nach ein geschlossener Ring, da seine Derivate, das Hexahydromesitylen und Hexahydromellithsäure, mit Leichtigkeit wieder in Benzolabkömmlinge übergeführt werden können.|trans-quote=During the reduction [of benzene] with sodium amalgam or phosphonium iodide, six atoms of hydrogen are added in the extreme case, and there arise derivatives, which derive from a hydrocarbon C₆H₁₂. This hydrocarbon is in all probability a closed ring, since its derivatives — hexahydromesitylene [1,3,5 - trimethyl cyclohexane] and hexahydromellithic acid [cyclohexane-1,2,3,4,5,6-hexacarboxylic acid] — can be converted with ease again into benzene derivatives.}}</ref> and pronounced the same reaction product "hexahydrobenzene". * In 1890 Vladimir Markovnikov believed he was able to distill the same compound from Caucasus petroleum, calling his concoction "hexanaphtene".{{citation needed|date=May 2023}}

Surprisingly, their cyclohexanes boiled higher by 10&nbsp;°C than either hexahydrobenzene or hexanaphthene, but this riddle was solved in 1895 by Markovnikov, N.M. Kishner, and Nikolay Zelinsky when they reassigned "hexahydrobenzene" and "hexanaphtene" as methylcyclopentane, the result of an unexpected rearrangement reaction.

:180px|reduction of benzene to methylcyclopentane|class=skin-invert

====Success==== In 1894, Baeyer synthesized cyclohexane starting with a ketonic decarboxylation of pimelic acid followed by multiple reductions:

:550px|1894 cyclohexane synthesis Baeyer|class=skin-invert

In the same year, E. Haworth and W.H. Perkin Jr. (1860–1929) prepared it via a Wurtz reaction of 1,6-dibromohexane.

:300px|1894 cyclohexane synthesis Perkin / haworth|class=skin-invert

==Reactions and uses== Although rather unreactive, cyclohexane undergoes autoxidation to give a mixture of cyclohexanone and cyclohexanol. The cyclohexanone&ndash;cyclohexanol mixture, called "''KA oil''", is a raw material for adipic acid and caprolactam, precursors to nylon. Several million kilograms of cyclohexanone and cyclohexanol are produced annually.<ref name=Ullmann>{{cite encyclopedia|author=Michael Tuttle Musser |encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=Wiley-VCH|location=Weinheim|year=2005|doi=10.1002/14356007.a08_217|isbn=978-3527306732 |chapter=Cyclohexanol and Cyclohexanone }}</ref>

It is used as a solvent in some brands of correction fluid. Cyclohexane is sometimes used as a non-polar organic solvent, although n-hexane is more widely used for this purpose. It is frequently used as a recrystallization solvent, as many organic compounds exhibit good solubility in hot cyclohexane and poor solubility at low temperatures.

Cyclohexane is also used for calibration of differential scanning calorimetry (DSC) instruments, because of a convenient crystal-crystal transition at −87.1&nbsp;°C.<ref>{{cite journal |first=D. M. |last=Price |title=Temperature Calibration of Differential Scanning Calorimeters |journal=Journal of Thermal Analysis |volume=45 |issue=6 |year=1995 |pages=1285–1296 |doi=10.1007/BF02547423 |s2cid=97402835 }}</ref>

Cyclohexane vapour is used in vacuum carburizing furnaces, in heat treating equipment manufacture.

==Conformation== {{main|Cyclohexane conformation}}

The 6-vertex edge ring does not conform to the shape of a perfect hexagon. The conformation of a flat 2D planar hexagon has considerable strain because the C-H bonds would be eclipsed. Therefore, to reduce torsional strain, cyclohexane adopts a three-dimensional structure known as the chair conformation, which rapidly interconvert at room temperature via a process known as a chair flip. During the chair flip, there are three other intermediate conformations that are encountered: the half-chair, which is the most unstable conformation, the more stable boat conformation, and the twist-boat, which is more stable than the boat but still much less stable than the chair. The chair and twist-boat are energy minima and are therefore conformers, while the half-chair and the boat are transition states and represent energy maxima. The idea that the chair conformation is the most stable structure for cyclohexane was first proposed as early as 1890 by Hermann Sachse, but only gained widespread acceptance much later. The new conformation puts the carbons at an angle of 109.5°. Half of the hydrogens are in the plane of the ring (''equatorial'') while the other half are perpendicular to the plane (''axial''). This conformation allows for the most stable structure of cyclohexane. Another conformation of cyclohexane exists, known as boat conformation, but it interconverts to the slightly more stable chair formation. If cyclohexane is mono-substituted with a large substituent, then the substituent will most likely be found attached in an equatorial position, as this is the slightly more stable conformation.

Cyclohexane has the lowest angle and torsional strain of all the cycloalkanes; as a result cyclohexane has been deemed a 0 in total ring strain.

===Solid phases=== Cyclohexane has two crystalline phases. The high-temperature phase I, stable between 186 K and the melting point 280 K, is a plastic crystal, which means the molecules retain some rotational degree of freedom. The low-temperature (below 186 K) phase II is ordered. Two other low-temperature (metastable) phases III and IV have been obtained by application of moderate pressures above 30 MPa, where phase IV appears exclusively in deuterated cyclohexane (application of pressure increases the values of all transition temperatures).<ref name=phase>{{cite journal|doi=10.1002/pssb.2221660207|title=Neutron Scattering Studies of C6H12 and C6D12 Cyclohexane under High Pressure|year=1991|last1=Mayer|first1=J.|last2=Urban|first2=S.|last3=Habrylo|first3=S.|last4=Holderna|first4=K.|last5=Natkaniec|first5=I.|last6=Würflinger|first6=A.|last7=Zajac|first7=W.|journal=Physica Status Solidi B|volume=166|issue=2|pages=381|bibcode=1991PSSBR.166..381M}}</ref>

{|class="wikitable" style="text-align:center" |+Cyclohexane phases<ref name=phase/> !No!!Symmetry!! Space group !! a (Å) !! b (Å) !! c (Å) !! Z !! T (K) !! P (MPa) |- | I || Cubic || Fm3m || 8.61 || || || 4 || 195 || 0.1 |- | II || Monoclinic || C2/c || 11.23 || 6.44 || 8.20 || 4 || 115 || 0.1 |- | III || Orthorhombic || Pmnn || 6.54 || 7.95 || 5.29 || 2 || 235 || 30 |- | IV || Monoclinic || P12(1)/n1 || 6.50 || 7.64 || 5.51 || 4 || 160 || 37 |}

Here Z is the number structure units per unit cell; the unit cell constants a, b and c were measured at the given temperature T and pressure P.

==See also== * The Flixborough disaster, a major industrial accident caused by an explosion of cyclohexane * Hexane *Ring flip * Cyclohexane (data page)

==References== <references/>

==External links== {{commons category|Cyclohexane}} *[http://www.inchem.org/documents/icsc/icsc/eics0242.htm International Chemical Safety Card 0242] * [https://web.archive.org/web/20060819025512/http://npi.gov.au/database/substance-info/profiles/30.html National Pollutant Inventory – Cyclohexane fact sheet] *[https://www.cdc.gov/niosh/npg/npgd0163.html NIOSH Pocket Guide to Chemical Hazards] *[http://www.3dchem.com/molecules.asp?ID=176 Cyclohexane@3Dchem] *[https://web.archive.org/web/20100707214900/http://www.chem.yale.edu/~chem125/125/history/Baeyer/Sachse.html Hermann Sachse] and the first suggestion of a chair conformation. *[https://www.nlm.nih.gov/toxnet/index.html NLM Hazardous Substances Databank – Cyclohexane] *[https://web.archive.org/web/20060409110115/http://www.labnews.co.uk/new_labnews/article.php?artid=1017&categoryid=2&scheme=2 Methanol Discovered in Space] * Calculation of [http://ddbonline.ddbst.de/AntoineCalculation/AntoineCalculationCGI.exe?component=Cyclohexane vapor pressure], [http://ddbonline.ddbst.de/DIPPR105DensityCalculation/DIPPR105CalculationCGI.exe?component=Cyclohexane liquid density], [http://ddbonline.ddbst.de/VogelCalculation/VogelCalculationCGI.exe?component=Cyclohexane dynamic liquid viscosity], [http://ddbonline.ddbst.de/DIPPR106SFTCalculation/DIPPR106SFTCalculationCGI.exe?component=Cyclohexane surface tension] of cyclohexane *[http://processflowsheet.com/cyclohexane-production-by-benzene-hydrogenation/ Cyclohexane production process flowsheet, benzene hydrogenation technique] {{cycloalkanes}}

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Category:Cycloalkanes Category:Hydrocarbon solvents Category:Commodity chemicals Category:Cyclohexanes