Cresol cation-radical

In contrast to p-cresol, o-cresol does not undergo oxidation under these conditions. The same restriction is true in the case of 4-hydroxy-3,4 -dimethylbiphenyl—only one methyl group undergoes oxidation, the one in position 4 (KosheF et al. 1997). The methyl group that is in position 3—ortho with respect to the hydroxy group—remains intact. Such inactivity is explained in terms of the cation-radical mechanism according to Scheme 7.50. 

The close relations between odd- and even-electron cations is shown in Scheme 9. Viewed in a retrosynthetic manner, the protonated cresols [7 + H]+, representing parent species for the ionic part of the distonic ions 24, can be generated by addition of an H atom to the radical cations 7 + as well as by addition of a proton to the neutral arenes 7. In the same way, the radical cations 22a, representing the ionic fragments of the McLafferty reaction, can be formed both by addition of H to the benzylic cations 9 and by addition of H+ to the benzylic radicals 25. 

A weak ortho effect The isomeric radical cations of ortfto-cresol also eliminate water but to lesser extents. 

Electron transfer oxidation of 4-methoxyphenol using wjeio-tetraphenylporphyrin as the electron acceptor brings about dehydrodimerization of the phenol to yield 5. The presence of the radical cation of the phenol has been detected by CIDNP techniques. The same product is obtained by irradiation of the tetraphenylporphyrin/benzoquinone/p-methoxyphenol system . Pyrimidinopteridine Af-oxide has been used as a sensitizer to effect the hydroxylation of phenols, also involving the radical cation of the phenol. Thus phenol can be converted to catechol and hydroquinone while cresol yields 4-methyl-catechol . Hydroquinone can itself be oxidized by the cobalt azide complex in aqueous... 

In an important discovery in the early 1990s, Cao and coworkers154 found that organic solvent solubility can be imparted to conducting PAn salts by the incorporation of surfactant-like dopant acids (HA). For example, by doping EB with large bifunctional protonic acids such as HCSA or DBSA, it is possible to solubilize fractions of these polymers in their fully doped state into solvents such as m-cresol, chloroform, toluene, and xylene. This solubilization is caused by the hydrocarbon tail in the dopants, while the sulfonate (SO,-) head forms an ionic bond with radical cation NH+ sites on the PAn chains. There is some debate as to whether this approach pro-... 

The mass spectra of aryl methanesulfonates were examined42 with the expectation of observing enhanced intensities for the ions at m/z 80 and m/z 97, if an ortho methyl group were present, e.g. in o-tolyl methanesulfonate (56). However, neither ions were formed but an intense signal at m/z 108 was ascribed to the radical cation of 0-cresol (equation 12), produced by loss of a neutral sulfene molecule. The ion at m/z 108 was the base peak in the mass spectrum of m-tolyl methanesulfonate, showing that the presence of a methyl group in the ortho position was not essential for its formation. The mass spectrum of 56 was... 

The primary resins used in this market are the radiation-curable epoxy acrylates, accounting for 60% of the resins used. A small amoimt of cycloaliphatic epoxies are also used in UV-curable inks and resists. Phenol and cresol epoxy no-volacs, and bisphenol A based epoxies are used in thermally cured formulations. The epoxy novolacs are used where higher heat resistance is needed such as in solder masks. Both free-radical and cationic-curable UV inks and colored base coats have grown rapidly because of the needs for higher line speeds, faster cleanup or line turnaround, less energy consumption, less capital for a new hne, and fewer emissions. 

The mass spectra of phenols usually show strong molecular ion peaks. In fact, the molecular ion at miz = 94 is the base peak in the El-MS of phenol (Fig. 4.34). Favored modes of fragmentation involve loss of a hydrogen atom to create an M - 1 peak (a small peak at mIz = 93), loss of carbon monoxide (CO) to produce a peak at M -28 (m/z = 66), and loss of a formyl radical (HCO-) to give a peak at M - 29. In the case of phenol itself, this creates the aromatic cyclopentadienyl cation at m/z = 65. In some cases, the loss of 29 mass units may be sequential initial loss of carbon monoxide followed by loss of a hydrogen atom. The mass spectrum of ortho-cresol (2-methylphenol) exhibits a much larger peak at M - 1 (Fig. 4.35) than does unsubstituted phenol. Note also the peaks at miz = 80 and m/z = 79 in the o-cresol spectrum from loss of CO and formyl radical, respectively. 

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