Xylylene dibromide explained

Xylylene dibromide is an organic compound with the formula C₆H₄(CH₂Br)₂. It is an off-white solid that, like other benzyl halides, a strong lachrymator. It is a useful reagent owing to the convenient reactivity of the two C-Br bonds.^[1] Two other isomers are known, para- and meta-xylylene dibromide.

Synthesis

It is prepared by the photochemical reaction of ortho-xylene with bromine:^[2]

C₆H₄(CH₃)₂ + 2Br₂ → C₆H₄(CH₂Br)₂ + 2 HBr

Reactions

Further bromination gives the tetrabromide:^[3]

C₆H₄(CH₂Br)₂ + 2Br₂ → 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.^[4]

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.^[5]

Coupling of xylylene dibromide by treatment with lithium metal gives dibenzocyclooctane, precursor to dibenzocyclooctadiene.^[6]

Related compounds

• Xylylene dichloride, the dichloro analogue of the title compound.
• Benzyl bromide, the simplest benzylic bromide.

References

1. 10.15227/orgsyn.047.0110. 2-(p-Tolylsulfonyl)dihydroisoindole. Organic Syntheses. 1967. 47. 110. J.. Bornstein. J. E.. Shields.
2. Emily F. M. Stephenson. 1954. o-Xylylene Dibromide. Organic Syntheses. 34. 100. 10.15227/orgsyn.034.0100.
3. 10.15227/orgsyn.034.0082. o-Phthalaldehyde. Organic Syntheses. 1954. 34. 82. J. C.. Bill. D. S.. Tarbell.
4. 10.1021/ja00838a015. 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. 1975. Mayerle. J. J.. Denmark. S. E.. Depamphilis. B. V.. Ibers. James A.. Holm. R. H.. Journal of the American Chemical Society. 97. 5. 1032–1045.
5. 10.1021/om00054a059. Formation of Iron Carbonyl Complexes of Reactive Polyenes from Dihalides involving the Free Polyene. 1991. Kerber. Robert C.. Ribakove. Everett C.. Organometallics. 10. 8. 2848–2853.
6. 10.15227/orgsyn.089.0055. Dibenzo[a,e]cyclooctene: Multi-gram Synthesis of a Bidentate Ligand . Organic Syntheses . 2012 . 89 . 55. Géraldine Franck, Marcel Brill, Günter Helmchen . free .