Xylenol

Xylenol or dimethylphenol is an arene compound with two methyl groups and a hydroxyl group. 6 isomers exist of xylenol of which 2,6-xylenol with both methyl group in an ortho position with respect to the hydroxyl group is the most important. The name xylenol is a contraction of two similar compounds xylene and phenol.

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Selected Properties

The physical properties of the 6 xylenol isomers are very similar.

Uses

Together with cresols and cresylic acid, xylenols are an important class of phenolics with great industrial importance. Xylenols are used as pesticides and used in the manufacture of antioxidants. Xylenol orange is a redox indicator built on a xylenol skeleton.

2,6-xylenol is a monomer for Poly(p-phenylene oxide) engineering resins through carbon - oxygen oxidative coupling. carbon to carbon dimerization is also possible. In one study 2,6-xylenol is oxidized with iodosobenzene diacetate with an 5 fold excess of the phenol ^[1].

In the first step of the proposed reaction mechanism the acetyl groups in the iodine compound are replaced with the phenol. This complex dissociates into an aryl radical anion and a phenoxy residue. The two aryl radicals recombine forming a new carbon carbon covalent bond and subsequently lose two protons in a rearomatization step. The immediate reaction product is a diphenoquinone as result of a one-step 4-electron oxidation. It is nevertheless possible to synthesize the biphenol compound via a comproportionation of the quinone with xylenol already present. In this reaction sequence the hypervalent iodine reagent is eventually reduced to phenyliodine.

3,5,3',5'-tetramethyl-biphenyl-4,49-diol is used as a reducing agent for silver in photographic applications and as a constituent in epoxy resins.

References

1. ^ Selective oxidative para C–C dimerization of 2,6-dimethylphenol Christophe Boldron, Guillem Aromí, Ger Challa, Patrick Gamez and Jan Reedijk Chemical Communications, 2005, (46), 5808 - 5810 Abstract