{{short description|Chemical compound}} {{Use dmy dates|date=September 2022}} {{chembox |Verifiedfields = changed |Watchedfields = changed |verifiedrevid = 477205894 |ImageFileL1 = P-Benzochinon.svg |ImageClassL1 = skin-invert-image |ImageSizeL1 = 60px |ImageNameL1 = Skeletal formula |ImageFileR1 = 1,4-benzoquinone-3D-vdW.png |ImageNameR1 = Space-filling model |ImageFile2 = Para-Benzoquinone needles.jpg |PIN = Cyclohexa-2,5-diene-1,4-dione<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 = 723–724 | doi = 10.1039/9781849733069-FP001 | isbn = 978-0-85404-182-4}}</ref> |OtherNames = 1,4-Benzoquinone<ref name=iupac2013 /><br />Benzoquinone<br />''p''-Benzoquinone<br />''p''-Quinone |Section1={{Chembox Identifiers |IUPHAR_ligand = 6307 |ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}} |ChEBI_Ref = {{ebicite|correct|EBI}} |ChEBI = 16509 |ChemSpiderID = 4489 |UNII_Ref = {{fdacite|correct|FDA}} |UNII = 3T006GV98U |KEGG_Ref = {{keggcite|correct|kegg}} |KEGG = C00472 |3DMet = B01254 |EC_number = 203-405-2 |UNNumber = 2587 |Gmelin = 2741 |Beilstein = 773967 |InChI = 1/C6H4O2/c7-5-1-2-6(8)4-3-5/h1-4H |InChIKey = AZQWKYJCGOJGHM-UHFFFAOYAR |SMILES1 = C1=CC(=O)C=CC1=O |ChEMBL_Ref = {{ebicite|correct|EBI}} |ChEMBL = 8320 |StdInChI_Ref = {{stdinchicite|correct|chemspider}} |StdInChI = 1S/C6H4O2/c7-5-1-2-6(8)4-3-5/h1-4H |StdInChIKey_Ref = {{stdinchicite|correct|chemspider}} |StdInChIKey = AZQWKYJCGOJGHM-UHFFFAOYSA-N |CASNo_Ref = {{cascite|correct|CAS}} |CASNo = 106-51-4 |PubChem = 4650 |SMILES = O=C\1\C=C/C(=O)/C=C/1 |RTECS = DK2625000 }} |Section2={{Chembox Properties |C=6 | H=4 | O=2 |Appearance = Yellow solid |Odor = Acrid, chlorine-like<ref name=PGCH/> |Density = 1.318 g/cm<sup>3</sup> at 20 °C |MeltingPtC = 115 |BoilingPt = Sublimes |Solubility = 11 g/L (18 °C) |SolubleOther = Slightly soluble in petroleum ether; soluble in acetone; 10% in ethanol, benzene, diethyl ether |VaporPressure = 0.1 mmHg (25 °C)<ref name=PGCH/> |MagSus = −38.4·10<sup>−6</sup> cm<sup>3</sup>/mol }} |Section3={{Chembox Hazards |MainHazards = Toxic |FlashPtF = 100 to 200 |FlashPt_ref = <ref name=PGCH/> |GHSPictograms = {{GHS06}}{{GHS07}}{{GHS09}} |GHSSignalWord = Danger |HPhrases = {{H-phrases|301|315|319|331|335|400}} |PPhrases = {{P-phrases|261|264|270|271|273|280|301+310|302+352|304+340|305+351+338|311|312|321|330|332+313|337+313|362|391|403+233|405|501}} |PEL = TWA 0.4 mg/m<sup>3</sup> (0.1 ppm)<ref name=PGCH>{{PGCH|0542}}</ref> |IDLH = 100 mg/m<sup>3</sup><ref name=PGCH/> |REL = TWA 0.4 mg/m<sup>3</sup> (0.1 ppm)<ref name=PGCH/> | LD50 = 296 mg/kg (mammal, subcutaneous)<br/>93.8 mg/kg (mouse, subcutaneous)<br/>8.5 mg/kg (mouse, IP)<br/>5.6 mg/kg (rat)<br/>130 mg/kg (rat, oral)<br/>25 mg/kg (rat, IV)<ref>{{IDLH|106514|Quinone}}</ref> }} |Section4={{Chembox Related |OtherFunction_label = Ketone |OtherCompounds = 1,2-Benzoquinone }} }}
'''1,4-Benzoquinone''', commonly known as '''''para''-quinone''', is a chemical compound with the formula C<sub>6</sub>H<sub>4</sub>O<sub>2</sub>. In a pure state, it forms bright-yellow crystals with a characteristic irritating odor, resembling that of chlorine, bleach, and hot plastic or formaldehyde. This six-membered ring compound is the oxidized derivative of 1,4-hydroquinone.<ref name=cv2p0553>{{ OrgSynth | author = Underwood, H. W. Jr. | author2 = Walsh, W. L. | title = Quinone | year = 1936 | volume = 16 | pages = 73 | collvol = 2 | collvolpages = 553 | doi=10.15227/orgsyn.002.0085 }}</ref> The molecule is multifunctional: it exhibits properties of a ketone, being able to form oximes; an oxidant, forming the dihydroxy derivative; and an alkene, undergoing addition reactions, especially those typical for α,β-unsaturated ketones. 1,4-Benzoquinone is sensitive toward both strong mineral acids and alkali, which cause condensation and decomposition of the compound.<ref>{{cite book |doi=10.1002/9780470772119|title=The Quinonoid Compounds: Vol. 1 (1988)|year=1988|isbn=978-0-470-77211-9|editor1-last=Patai|editor1-first=Saul|editor2-last=Rappoport|editor2-first=Zvi}}</ref><ref>{{cite book |doi=10.1002/9780470772126|title=The Quinonoid Compounds: Vol. 2 (1988)|year=1988|isbn=978-0-470-77212-6|editor1-last=Patai|editor1-first=Saul|editor2-last=Rappoport|editor2-first=Zvi}}</ref>
==Preparation== 1,4-Benzoquinone is prepared industrially by oxidation of hydroquinone, which can be obtained by several routes. One route involves oxidation of diisopropylbenzene and the Hock rearrangement. The net reaction can be represented as follows: :<chem>C6H4(CHMe2)2 + 3 O2 -> C6H4O2 + 2 OCMe2 + H2O</chem> The reaction proceeds via the bis(hydroperoxide) and the hydroquinone. Acetone is a coproduct.<ref>Gerhard Franz, Roger A. Sheldon "Oxidation" in ''Ullmann's Encyclopedia of Industrial Chemistry'', Wiley-VCH, Weinheim, 2000 {{doi|10.1002/14356007.a18_261}}</ref>
Another major process involves the direct hydroxylation of phenol by acidic hydrogen peroxide: :<chem>C6H5OH + H2O2 -> C6H4(OH)2 + H2O</chem> Both hydroquinone and catechol are produced. Subsequent oxidation of the hydroquinone gives the quinone.<ref name=Ullmann>Phillip M. Hudnall "Hydroquinone" in ''Ullmann's Encyclopedia of Industrial Chemistry'', 2002, Wiley-VCH, Weinheim. 2005 Wiley-VCH, Weinheim. {{doi|10.1002/14356007.a13_499}}.</ref>
1,4-Benzoquinone was originally prepared industrially by oxidation of aniline, for example by manganese dioxide.<ref name=IARC>{{ Cite book | url = http://monographs.iarc.fr/ENG/Monographs/vol71/mono71-63.pdf | chapter = 1,4-Benzoquinone (para-Quinone)|title=Re-evaluation of Some Organic Chemicals, Hydrazine and Hydrogen Peroxide (Part 1, Part 2, Part 3) | series = IARC Monographs }}</ref> This method is mainly practiced in China where environmental regulations are more relaxed.
Oxidation of hydroquinone is facile.<ref name=cv2p0553/><ref>{{ OrgSynth | author = Vliet, E. B. | title = Quinone | year = 1922 | volume = 2 | pages = 85 | collvol = 1 | collvolpages = 482 | doi=10.15227/orgsyn.016.0073 }}</ref> One such method makes use of hydrogen peroxide as the oxidizer and iodine or an iodine salt as a catalyst for the oxidation occurring in a polar solvent such as isopropyl alcohol.<ref>{{ cite patent | country = US | status = patent | number = 4973720 | title = Process for the preparation of p-benzoquinone }}</ref>
When heated to near its melting point, 1,4-benzoquinone sublimes, even at atmospheric pressure, allowing for an effective purification. Impure samples are often dark-colored due to the presence of quinhydrone, a dark green 1:1 charge-transfer complex of quinone with hydroquinone.<ref>{{cite journal|author=Sakurai, T.|title=On the refinement of the crystal structures of phenoquinone and monoclinic quinhydrone|journal=Acta Crystallographica Section B |year=1968| volume=24|issue=3| pages=403–412 | doi=10.1107/S0567740868002451|bibcode=1968AcCrB..24..403S }}</ref>
==Structure and redox== class=skin-invert-image|thumb|left|C–C and C–O bond distances in benzoquinone (Q), its 1e reduced derivative (Q<sup>−</sup>), and hydroquinone (H<sub>2</sub>Q).<ref name=Kochi/> Benzoquinone is a planar molecule with localized, alternating C=C, C=O, and C–C bonds. Reduction gives the semiquinone anion C<sub>6</sub>H<sub>4</sub>O<sub>2</sub><sup>−</sup>}, which adopts a more delocalized structure. Further reduction coupled to protonation gives the hydroquinone, in which the electrons of the C6 ring are fully delocalized.<ref name=Kochi>{{cite journal | doi = 10.1021/ja066471o| pmid = 17177421| title = Quinones as Electron Acceptors. X-Ray Structures, Spectral (EPR, UV−vis) Characteristics and Electron-Transfer Reactivities of Their Reduced Anion Radicals as Separated vs Contact Ion Pairs| journal = Journal of the American Chemical Society| volume = 128| issue = 51| pages = 16708–19| year = 2006| last1 = Lü| first1 = Jian-Ming| last2 = Rosokha| first2 = Sergiy V| last3 = Neretin| first3 = Ivan S| last4 = Kochi| first4 = Jay K}}</ref>
==Reactions and applications== Benzoquinonium is a skeletal muscle relaxant, ganglion blocking agent that is made from benzoquinone.<ref name="CavallitoSoria1950">{{cite journal|last1=Cavallito|first1=Chester J.|last2=Soria|first2=Albert E.|last3=Hoppe|first3=James O.|title=Amino- and Ammonium-alkylaminobenzoquinones as Curarimimetic Agents|journal=Journal of the American Chemical Society|volume=72|issue=6|year=1950|pages=2661–2665|issn=0002-7863|doi=10.1021/ja01162a088}}</ref>
===Organic synthesis=== It is used as a hydrogen acceptor and oxidant in organic synthesis.<ref>{{ cite encyclopedia |author1=Yang, T.-K. |author2=Shen, C.-Y. | encyclopedia = Encyclopedia of Reagents for Organic Synthesis | editor = L. Paquette | year = 2004 | publisher = J. Wiley & Sons | location = New York | doi = 10.1002/047084289X.rb033 |chapter=1,4-Benzoquinone |isbn=978-0-471-93623-7 }}</ref> 1,4-Benzoquinone serves as a dehydrogenation reagent. It is also used as a dienophile in Diels-Alder reactions.<ref>{{ OrgSynth | author = Oda, M. | author2 = Kawase, T. | author3 = Okada, T. | author4 = Enomoto, T. | title = 2-Cyclohexene-1,4-dione | year = 1996 | volume = 73 | pages = 253 | collvol = 9 | collvolpages = 186 | doi=10.15227/orgsyn.073.0253 }}</ref>
Benzoquinone reacts with acetic anhydride and sulfuric acid to give the triacetate of hydroxyquinol.<ref>{{cite journal|last1=Vliet|first1=E. B.|title=Hydroquinone Triacetate|journal=Organic Syntheses|date=1941|volume=1|page=317|doi=10.15227/orgsyn.004.0035}}</ref><ref>{{cite web|last1=Knowles|first1=M. B.|title=Process for production of 2,4,5-trihydroxyacetophenone|date=1952|url=https://drive.google.com/viewerng/viewer?url=patentimages.storage.googleapis.com/pdfs/US2763691.pdf|website=Google Patents|publisher=Eastman Kodak Co.|accessdate=24 December 2014}}</ref> This reaction is called the '''Thiele reaction''' or '''Thiele–Winter reaction'''<ref>{{cite book|last1=McOmie|first1=J. F. W.|last2=Blatchly|first2=J. M.|title=Organic Reactions |chapter=The Thiele-Winter Acetoxylation of Quinones | volume = 19|pages=199–277|doi=10.1002/0471264180.or019.03|isbn=978-0-471-19619-8|year=2011}}</ref><ref>{{ cite journal | author = Thiele, J. | title = Ueber die Einwirkung von Essigsäure-anhydrid auf Chinon und auf Dibenzoylstyrol | journal = Berichte der Deutschen Chemischen Gesellschaft | year = 1898 | volume = 31 | issue = 1 | pages = 1247–1249 | doi = 10.1002/cber.189803101226 | url = https://zenodo.org/record/1425900 }}</ref> after Johannes Thiele, who first described it in 1898, and after Ernst Winter, who further described its reaction mechanism in 1900. An application is found in this step of the total synthesis of Metachromin A:<ref>{{ cite journal | last1 = Almeida | first1 = W. P. | last2 = Correia | first2 = C. R. D. | title = Stereoselective Total Synthesis and Enantioselective Formal Synthesis of the Antineoplastic Sesquiterpene Quinone Metachromin A | journal = Journal of the Brazilian Chemical Society | year = 1999 | volume = 10 | issue = 5 | pages = 401–414 | doi = 10.1590/S0103-50531999000500011 | url = http://www.scielo.br/pdf/jbchs/v10n5/a11v10n5.pdf | doi-access = free }}</ref>
:class=skin-invert-image|400px|left|An application of the Thiele reaction, involving a benzoquinone derivative.
Benzoquinone is also used to suppress double-bond migration during olefin metathesis reactions.
An acidic potassium iodide solution reduces a solution of benzoquinone to hydroquinone, which can be reoxidized back to the quinone with a solution of silver nitrate.
Due to its ability to function as an oxidizer, 1,4-benzoquinone can be found in methods using the Wacker-Tsuji oxidation, wherein a palladium salt catalyzes the conversion of an alkene to a ketone. This reaction is typically carried out using pressurized oxygen as the oxidizer, but benzoquinone can sometimes preferred. It is also used as a reagent in some variants on Wacker oxidations.
1,4-Benzoquinone is used in the synthesis of Bromadol and related analogs.
thumb|left|Structure of Cp*Rh(para-quinone).<ref>{{cite journal|title=η<sup>5</sup>-Semiquinone Complexes and the Related η4-Benzoquinone of (Pentamethylcyclopentadienyl)rhodium and -iridium: Synthesis, Structures, Hydrogen Bonding, and Electrochemical Behavior |first1=Jamal|last1=Moussa|first2=Carine|last2=Guyard-Duhayon|first3=Patrick|last3=Herson|first4=Hani|last4=Amouri|first5=Marie Noelle |last5=Rager|first6=Anny|last6=Jutand|journal=Organometallics|year=2004|volume=23|issue=26|pages=6231–6238|doi=10.1021/om049292t}}</ref>
==Related 1,4-benzoquinones== {{see|Quinone}} 2,3-Dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) is a stronger oxidant and dehydrogenation agent than 1,4-benzoquinone.<ref>{{OrgSynth | author = Vogel, E. | author2 = Klug, W. | author3 = Breuer, A. | title = <nowiki>1,6-Methano[10]annulene</nowiki> | year = 1974 | volume = 54 | pages = 11 | collvol = 6 | collvolpages = 731 | doi=10.15227/orgsyn.054.0011 }}</ref> Chloranil 1,4-C<sub>6</sub>Cl<sub>4</sub>O<sub>2</sub> is another potent oxidant and dehydrogenation agent. Monochloro-p-benzoquinone is yet another but milder oxidant.<ref>{{ OrgSynth | author = Harman, R. E. | title = Chloro-p-benzoquinone | year = 1955 | volume = 35 | page = 22 | collvol = 4 | collvolpages = 148 | doi=10.15227/orgsyn.035.0022 }}</ref>
==Metabolism== 1,4-Benzoquinone is a toxic metabolite found in human blood and can be used to track exposure to benzene or mixtures containing benzene and benzene compounds, such as petrol.<ref>{{ cite journal | last1 = Lin | first1 = Y. S. | last2 = McKelvey | first2 = W. | last3 = Waidyanatha | first3 = S. | last4 = Rappaport | first4 = S. M. | title = Variability of Albumin Adducts of 1,4-Benzoquinone, a Toxic Metabolite of Benzene, in Human Volunteers | journal = Biomarkers | year = 2006 | volume = 11 | issue = 1 | pages = 14–27 | doi = 10.1080/13547500500382975 | pmid = 16484134 | s2cid = 13198966 }}</ref> The compound can interfere with cellular respiration, and kidney damage has been found in animals receiving severe exposure. It is excreted in its original form and also as variations of its own metabolite, hydroquinone.<ref name=IARC/>
==Safety== [[File:Brachinus spPCCA20060328-2821B.jpg|thumb|left|The bombardier beetle sprays 1,4-benzoquinone to deter predators]] 1,4-Benzoquinone is able to stain skin dark brown, cause erythema (redness, rashes on skin) and lead on to localized tissue necrosis. It is particularly irritating to the eyes and respiratory system. Its ability to sublime at commonly encountered temperatures allows for a greater airborne exposure risk than might be expected for a room-temperature solid. IARC has found insufficient evidence to comment on the compound's carcinogenicity, but has noted that it can easily pass into the bloodstream and that it showed activity in depressing bone marrow production in mice and can inhibit protease enzymes involved in cellular apoptosis.<ref name=IARC />
==See also== *Tetrahydroxybenzoquinone *Benzoquinonetetracarboxylic acid *1,2-Benzoquinone *Quinones *Duroquinone *Ardisiaquinone
==References== {{reflist}}
{{DEFAULTSORT:Benzoquinone, 1,4-}} Category:1,4-Benzoquinones Category:Oxidizing agents Category:Enones