Xylenol

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Xylenol are organic compounds with the formula (CH3)2C6H3OH. They are volatile colorless solids or oily liquids. They are derivatives of phenol with two methyl groups and a hydroxyl group. Six isomers exist, 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 portmanteau of the words xylene and phenol.

2,4-dimethylphenol together with other xylenols and many other compounds are traditionally extracted from coal tar, the volatile materials obtained in the production of coke from coal. These residue contains a few percent by weight of xylenols as well as cresols and phenol. The main xylenols in such tar are the 3,5-, 2,4, and 2,3- isomers. 2,6-Xylenol is produced by methylation of phenol using methanol in the presence of metal oxide catalysts:[1]

C6H5OH + 2 CH3OH → (CH3)2C6H3OH + 2 H2O

Properties[edit]

The physical properties of the six isomeric xylenols are similar.

Isomer 2,6-Xylenol 2,5-Xylenol 2,4-Xylenol 2,3-Xylenol 3,4-Xylenol 3,5-Xylenol
Structure 2,6-Xylenol.svg 2,5-Xylenol.svg 2,4-Xylenol.svg 2,3-Xylenol.svg 3,4-Xylenol.svg 3,5-Xylenol.svg
CAS 576-26-1 95-87-4 105-67-9 526-75-0 95-65-8 108-68-9
Mp °C 43-45 63 - 65 22-23 70-73 62 - 68 61-64
Bp °C 203 212 211-212 217 227 222
pKa [2] 10.59 10.22 10.45 10.50 10.32 10.15
Density g/mL 0.971 1.011

Uses[edit]

Together with cresols and cresylic acid, xylenols are an important class of phenolics with great industrial importance. They are 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) (PEO) engineering resins through carbon-oxygen oxidative coupling.

References[edit]

  1. ^ Helmut Fiegein "Cresols and Xylenols" in Ullmann's Encyclopedia of Industrial Chemistry, 2007; Wiley-VCH, Weinheim. doi:10.1002/14356007.a08_025
  2. ^ CRC Handbook of Tables for Organic Compound Identification, Third Edition, 1984, ISBN 0-8493-0303-6.

See also[edit]

External links[edit]