xylylene dibromide
{{Chembox
| ImageFile = C6H4(CH2Br)2.svg
| ImageSize =
| ImageAlt =
| OtherNames =
| IUPACName =
| Section1 = {{Chembox Identifiers
| CASNo = 91-13-4
| CASNo_Ref = {{Cascite|correct|CAS}}
| ChemSpiderID = 60032
| EINECS = 202-042-7
| PubChem = 66665
| UNII = 9FRJ55E5UL
| StdInChI=1S/C8H8Br2/c9-5-7-3-1-2-4-8(7)6-10/h1-4H,5-6H2
| StdInChIKey = KGKAYWMGPDWLQZ-UHFFFAOYSA-N
| SMILES = C1=CC=C(C(=C1)CBr)CBr
}}
| Section2 = {{Chembox Properties
| C=8|H=8|Br=2
| MolarMass =
| Appearance = off-white solid
| Density =
| MeltingPtC = 93-94
| BoilingPt =
| Solubility = }}
| Section3 = {{Chembox Hazards
| GHSPictograms = {{GHS05}}{{GHS07}}
| GHSSignalWord = Danger
| HPhrases = {{H-phrases|302|314}}
| PPhrases = {{P-phrases|260|264|270|280|301+312|301+330+331|303+361+353|304+340|305+351+338|310|321|330|363|405|501}}
| MainHazards = lachrymator
| FlashPt =
| AutoignitionPt = }}
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Xylylene dibromide is an organic compound with the formula C6H4(CH2Br)2. It is an off-white solid that, like other benzyl halides, is strongly lachrymatory. It is a useful reagent owing to the convenient reactivity of the two C-Br bonds.{{cite journal |doi=10.15227/orgsyn.047.0110|title=2-(p-Tolylsulfonyl)dihydroisoindole|journal=Organic Syntheses|year=1967|volume=47|page=110|first1=J.|last1=Bornstein|first2=J. E.|last2=Shields}} Two other isomers are known, para- and meta-xylylene dibromide.
Synthesis
It is prepared by the photochemical reaction of ortho-xylene with bromine:{{cite journal|author=Emily F. M. Stephenson|year=1954|title=o-Xylylene Dibromide|journal=Organic Syntheses|volume=34|page=100|doi=10.15227/orgsyn.034.0100}}
:C6H4(CH3)2 + 2{{nbsp}}Br2 → C6H4(CH2Br)2 + 2 HBr
Reactions
Further bromination gives the tetrabromide:{{cite journal |doi=10.15227/orgsyn.034.0082|title=o-Phthalaldehyde|journal=Organic Syntheses|year=1954|volume=34|page=82|first1=J. C.|last1=Bill|first2=D. S.|last2=Tarbell}}
:C6H4(CH2Br)2 + 2{{nbsp}}Br2 → C6H4(CHBr2)2 + 2 HBr
Upon reaction with thiourea followed by hydrolysis of the intermediate bisisothiouronium salts, xylylene dibromide can be converted to the dithiol C6H4(CH2SH)2.{{cite journal |doi=10.1021/ja00838a015|title=Synthetic Analogs of the Active Sites of Iron-Sulfur Proteins. XI. Synthesis and Properties of Complexes Containing the Iron Sulfide (Fe2S2) Core and the Structures of Bis[o-Xylyl-α,α'-Dithiolato-μ-Sulfido-Ferrate(III)] and bis[p-Tolylthiolato-μ-Sulfido-Ferrate(III)] Dianions|year=1975|last1=Mayerle|first1=J. J.|last2=Denmark|first2=S. E.|last3=Depamphilis|first3=B. V.|last4=Ibers|first4=James A.|last5=Holm|first5=R. H.|journal=Journal of the American Chemical Society|volume=97|issue=5|pages=1032–1045}}
Xylylene dibromide is a precursor to the ephemeral molecule ortho-quinonedimethane, also known as xylylene. This species can be trapped when the dehalogenation is conducted in the presence of iron carbonyl.{{cite journal|doi=10.1021/om00054a059|title=Formation of Iron Carbonyl Complexes of Reactive Polyenes from Dihalides involving the Free Polyene|year=1991|last1=Kerber|first1=Robert C.|last2=Ribakove|first2=Everett C.|journal=Organometallics|volume=10|issue=8|pages=2848–2853}}
Coupling of xylylene dibromide by treatment with lithium metal gives dibenzocyclooctane, precursor to dibenzocyclooctatetraene.{{cite journal |doi=10.15227/orgsyn.089.0055|title=Dibenzo[a,e]cyclooctene: Multi-gram Synthesis of a Bidentate Ligand |journal=Organic Syntheses |year=2012 |volume=89 |page=55|author=Géraldine Franck, Marcel Brill, Günter Helmchen |doi-access=free }}
Related compounds
- Xylylene dichloride, the dichloro analogue of the title compound.
- Benzyl bromide, the simplest benzylic bromide.