2,2,4-Trimethylpentane

{{short description|Chemical compound}} {{for|other isomers of octane|Octane#Isomers}} {{Chembox | Verifiedfields = changed | Watchedfields = changed | verifiedrevid = 477209668 | ImageFile = 2,2,4-Trimethylpentane.svg | ImageClass = skin-invert-image | ImageFile_Ref = {{chemboximage|correct|??}} | ImageSize = 160 | ImageName = Skeletal formula of 2,2,4-trimethylpentane | ImageFile1 = Isooctane-3D-balls.png | ImageClass1 = bg-transparent | ImageFile1_Ref = {{chemboximage|correct|??}} | ImageSize1 = 160 | ImageName1 = Ball and stick model of 2,2,4-trimethylpentane | ImageFile2 = Isooctane-3D-vdW.png | ImageClass2 = bg-transparent | ImageFile2_Ref = {{chemboximage|correct|??}} | ImageSize2 = 160 | ImageName2 = Spacefill model of 2,2,4-trimethylpentane | PIN = 2,2,4-Trimethylpentane<ref>{{cite web|title=2,2,4-trimethylpentane - Compound Summary|url=https://pubchem.ncbi.nlm.nih.gov/compound/10907|work=PubChem Compound|publisher=National Center for Biotechnology Information|access-date=11 March 2012|location=USA|date=26 March 2005|at=Identification and Related Records}}</ref> |Section1={{Chembox Identifiers | CASNo = 540-84-1 | CASNo_Ref = {{cascite|correct|CAS}} | UNII_Ref = {{fdacite|correct|FDA}} | UNII = QAB8F5669O | PubChem = 10907 | ChemSpiderID = 10445 | ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} | EINECS = 208-759-1 | UNNumber = 1262 | MeSHName = 2,2,4-trimethylpentane | ChEBI = 62805 | ChEBI_Ref = {{ebicite|changed|EBI}} | ChEMBL = 1797261 | ChEMBL_Ref = {{ebicite|changed|EBI}} | RTECS = SA3320000 | Beilstein = 1696876 | SMILES = CC(C)CC(C)(C)C | StdInChI = 1S/C8H18/c1-7(2)6-8(3,4)5/h7H,6H2,1-5H3 | StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} | StdInChIKey = NHTMVDHEPJAVLT-UHFFFAOYSA-N | StdInChI_Ref = {{stdinchicite|correct|chemspider}} }} |Section2={{Chembox Properties | C=8 | H=18 | Appearance = Colorless liquid | Odor = petroleum-like | Density = 0.692 g cm−3 | MeltingPtK = 165.77 | BoilingPtK = 372.45 | LogP = 4.373 | VaporPressure = 5.5 kPa (at 21 °C) | HenryConstant = 3.0 nmol Pa−1 kg−1 | LambdaMax = 210 nm | RefractIndex = 1.391 | MagSus = −98.34·10−6 cm3/mol }} |Section3={{Chembox Thermochemistry | DeltaHf = −260.6 to −258.0 kJ mol−1 | DeltaHc = −5462.6 to −5460.0 kJ mol−1 | Entropy = 328.03 J K−1 mol−1 | HeatCapacity = 242.49 J K−1 mol−1 }} |Section4={{Chembox Hazards | GHSPictograms = {{GHS flame}} {{GHS exclamation mark}} {{GHS health hazard}} {{GHS environment}} | GHSSignalWord = '''DANGER''' | HPhrases = {{H-phrases|225|304|315|336|410}} | PPhrases = {{P-phrases|210|261|273|301+310|331}} | NFPA-H = 1 | NFPA-F = 3 | NFPA-R = 0 | FlashPtC = −12 | AutoignitionPtC = 396 | ExploLimits = 1.1–6.0% }} |Section5={{Chembox Related | OtherFunction_label = alkanes | OtherFunction = {{Unbulleted list|2,2-Dimethylbutane|2,3-Dimethylbutane|Triptane|Tetramethylbutane|Tetraethylmethane|2,3,3-Trimethylpentane|2,3,4-Trimethylpentane|Tetra-''tert''-butylmethane|2,3-Dimethylhexane|2,5-Dimethylhexane}} }} }} '''2,2,4-Trimethylpentane''', also known as '''isooctane''' or '''iso-octane''', is an organic compound with the formula (CH3)3CCH2CH(CH3)2. It is one of several isomers of octane (C8H18). This particular isomer is the standard 100 point on the octane rating scale (the zero point is ''n''-heptane). It is an important component of gasoline, frequently used in relatively large proportions (around 10%) to increase the knock resistance of fuel.<ref>{{cite encyclopedia|author1=Werner Dabelstein |author2=Arno Reglitzky |author3=Andrea Schütze |author4=Klaus Reders|title=Automotive Fuels|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|year=2007|publisher=Wiley-VCH|location=Weinheim|doi=10.1002/14356007.a16_719.pub2|isbn=978-3527306732 }}</ref><ref>{{cite journal |last1=Richardson |first1=KA |last2=Wilmer |first2=JL |last3=Smith-Simpson |first3=D |last4=Skopek |first4=TR |title=Assessment of the genotoxic potential of unleaded gasoline and 2,2,4-trimethylpentane in human lymphoblasts in vitro. |journal=Toxicology and Applied Pharmacology |date=February 1986 |volume=82 |issue=2 |pages=316–22 |doi=10.1016/0041-008x(86)90207-3 |pmid=3945956 |bibcode=1986ToxAP..82..316R }}</ref>

Strictly speaking, if the standard meaning of "iso" is followed, the name ''isooctane'' should be reserved for the isomer 2-methylheptane. However, 2,2,4-trimethylpentane is by far the most important isomer of octane and historically it has been assigned this name.<ref>{{cite book|last=Clayden|first=Jonathan|title=Organic chemistry|year=2005|publisher=Oxford Univ. Press|location=Oxford [u.a.]|isbn=978-0-19-850346-0|pages=[https://archive.org/details/organicchemistry00clay_0/page/315 315]|edition=Reprinted (with corrections).|url-access=registration|url=https://archive.org/details/organicchemistry00clay_0/page/315}}</ref>

==Production== Isooctane is produced on a massive scale in the petroleum industry by alkylation of isobutene with isobutane. This process is conducted in alkylation units in the presence of acid catalysts.<ref>{{cite encyclopedia|title=Alkylation|author1=Bipin V. Vora |author2=Joseph A. Kocal |author3=Paul T. Barger |author4=Robert J. Schmidt |author5=James A. Johnson|year=2003|encyclopedia=Kirk-Othmer Encyclopedia of Chemical Technology|doi=10.1002/0471238961.0112112508011313.a01.pub2|isbn=0471238961 }}</ref> :[[File:Route2,2,4-Me3pentane.svg|thumb|class=skin-invert-image|left|400px|Route to 2,2,4-trimethylpentane from isobutene and isobutane]]{{clear-left}}

It can also be produced from isobutylene by dimerization using an Amberlyst catalyst to produce a mixture of iso-octenes. Hydrogenation of this mixture produces 2,2,4-trimethylpentane.<ref>[http://www.amberlyst.com/isooctane.htm Dimerization of isobutylene], Amberlyst.com</ref> {{Clear left}}

==History== Engine knocking is an unwanted process that can occur during high compression ratios in internal combustion engines. During the 1920s different measurement methods of knock were proposed but laboratories struggled to reproduce them reliably.

In 1926 Ethyl Corporation's Graham Edgar selected two specific hydrocarbons, ''n''-heptane (commercially available in high purity from Jeffrey pine) and 2,2,4-trimethylpentane, itself first synthesized from tert-butyl alcohol via diisobutene by J. W. McKinney at the same laboratory in the same year, as primary standards. Compared to various chemicals and natural gasolines proposed before that, these two compounds had extremely close boiling points, ensuring the vapor mixture in the cylinder would be the same regardless of the carburetor, and didn't depend on the composition of particular crudes.<ref>{{Cite web |date=1927-01-01|title=Measurement of Knock Characteristics of Gasoline in Terms of a Standard Fuel1|url=https://pubs.acs.org/doi/pdf/10.1021/ie50205a049|access-date=2026-04-26|website=ACS Publications|language=en|doi=10.1021/ie50205a049}}</ref>

This method became known as the octane rating scale. Test motors using 2,2,4-trimethylpentane gave a certain performance that was standardized as 100 octane. The same test motors, run in the same fashion, using heptane, gave a performance which was standardized as 0 octane. All other fuels were then graded against mixtures of these two chemicals and assigned octane numbers.<ref>{{Cite journal |last=Brooks |first=Donald B. |date=1946 |title=Development of REFERENCE FUEL SCALES for KNOCK RATING |url=https://www.jstor.org/stable/44548282 |journal=SAE Transactions |volume=54 |pages=394–403 |issn=0096-736X}}</ref><ref>[https://books.google.com/books?id=J_AkNu-Y1wQC&dq=Graham+Edgar+2%2C2%2C4-trimethylpentane&pg=PA62 Fuels and lubricants handbook], Volume 1, George E. Totten, Steven R. Westbrook, Rajesh J. Shah, page 62</ref>

==Safety== In common with all hydrocarbons, 2,2,4-trimethylpentane is flammable.<ref>[https://web.archive.org/web/20000823050150/http://www.epa.gov/iris/subst/0614.htm 2,2,4-Trimethylpentane], Integrated Risk Information System, United States Environmental Protection Agency</ref>

==See also== * Oil refinery * Antiknock agents

==References== {{Reflist}}

==External links== {{Commons category|2,2,4-Trimethylpentane}} *[http://www.inchem.org/documents/icsc/icsc/eics0496.htm International Chemical Safety Card 0496]

{{DEFAULTSORT:Trimethylpentane, 2,2,4-}} Category:Alkanes Category:Antiknock agents