Oxygen of phenols

A study of biomimetic oxygenations of phenol and indol derivatives has featured theoretical investigation of the charge-transfer complexes formed between carbanions and molecular oxygen (organodioxide anions).20... 

Many compounds involve combinations of the preceding resonance types. Figure 3.21 shows resonance structures for the anion that results from removing a proton (H+) from the oxygen of phenol. 

In the previous section, oxygenation of phenols with dioxygen catalyzed by metal complexes was described. From industrial and biological points of view, metal-complex catalyzed oxidation of phenols has also been performed using hydrogen peroxide or ferf-butyl hydroperoxide instead of dioxygen. Some examples are described briefly in this section. 

There has been considerable interest in the hydroxylation of phenol through a variety of approaches. The oxygenation of phenol in acetonitrile in the presence of cuprous chloride in catalytic quantities gave, after work-up by acidification, catechol in yields of 70-90% (ref.1) by way of a copper (II) intermediate. 

Oxygenation of Phenols (Model Reactions for Phenolase Reaction)... 

Figure 9. Mechanism of Co(II) Salen-catalyzed oxygenation of phenols.

The bifurcation is of HSAB origin. The iron atom in ferricyanide is quite soft since it is surrounded by sbc cyanide ligands and formal negative charges are present in the anionic cluster. Consequently, the interaction of the iron with the hard oxygen of phenol (phenolate) is unfavorable (symbiotically destabilized). The iron atom of ferric chloride is hard, and the exchange of its ligands with phenols is easy. 

Similarly to the base-catalyzed oxygenation of phenols (see Chapter 5.1. ), dioxygen attacks the keto-tautomer 18 to give peroxide 19, which transforms to cleavage products ... 

Nishinaga, a., T. Shimizu, and T. Matsuura Reaction of Potassium Superoxide with Phenoxy Radicals. On the Mechanism of Base-Catalyzed Oxygenation of Phenols. Chem. Letts 1977, 547. 

An efficient catalytic system for oxygenation of phenols to p- or o-quinones with molecular oxygen was achieved by utilization of a catalyst consisting of Co(OAc)2 and the multidentate N-heterocyclic podand ligand, A,A -bis-2-(2-pyridyl)ethyl)-2,6-pyridinedicarboxamide, 2-BPEPA (Figure... 

Xie M, Yang X, Zou C, Wu C (2011) A SnIV-porphyrin-based metal-organic fiamework for the selective photo-oxygenation of phenol and sulfides. Inorg Chem 50 5318-5320... 

---