Xylylene dibromide

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.^[1] Two other isomers are known, para- and meta-xylylene dibromide.

Xylylene dibromide

Identifiers
CAS Number	91-13-4 Y
3D model (JSmol)	Interactive image
ChemSpider	60032
ECHA InfoCard	100.001.857
EC Number	202-042-7
PubChem CID	66665
UNII	9FRJ55E5UL
CompTox Dashboard (EPA)	DTXSID2059019
InChI InChI=1S/C8H8Br2/c9-5-7-3-1-2-4-8(7)6-10/h1-4H,5-6H2 Key: KGKAYWMGPDWLQZ-UHFFFAOYSA-N
SMILES C1=CC=C(C(=C1)CBr)CBr
Properties
Chemical formula	C8H8Br2
Molar mass	263.960 g·mol−1
Appearance	off-white solid
Melting point	93–94 °C (199–201 °F; 366–367 K)
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	lachrymator
GHS labelling:
Pictograms
Signal word	Danger
Hazard statements	H302, H314
Precautionary statements	P260, P264, P270, P280, P301+P312, P301+P330+P331, P303+P361+P353, P304+P340, P305+P351+P338, P310, P321, P330, P363, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis

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

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

Reactions

Further bromination gives the tetrabromide:^[3]

C₆H₄(CH₂Br)₂ + 2 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.^[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 dibenzocyclooctatetraene.^[6]

Related compounds

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