Phenol hydroxylation reaction pathway

The QSAR models for phenols using resonance constants are apparently more accurate than QSAR models using Hammett constants. The R2 values for QSAR models using resonance constants, oresonancer and Hammett constants, a, were 0.9492 and 0.5473, respectively. The R2 value demonstrates that the QSAR model using resonance constants has a better fit. Figure 5.25 shows the reaction pathway for hydroxyl radical attack on phenols. 

Reaction pathway for substituted phenols reacting with hydroxyl radical. 

The plot shown in Figure 9.18 for the kinetics of COz formation from hydroxyl radical attack on chlorinated phenols appears to be random. This can be justified by the various intermediates formed along the reaction pathway. Each of these intermediates will have different degradation rates, so COz formation will be different according the reaction. 

Figure 10 Reactions of phenolates with /u.-ri ri -peto o complex (7) yields an ort/ro-hydroxylation reaction reminiscent of Tyr, while reactions of phenols by both (7) and his-/r-oxo complex (8) results in ort/ro-phenol coupled dimers through an apparent PCET pathway...

The Ag state of oxygen reacts with organic compounds and polymers in five characteristic reaction pathways hydrogen abstraction and addition (the ene reaction, equation 1), 1,4-cycloaddition (equation 2), 1,2 cyclo-addition (equation 3), oxygenation (equation 4) and hydrogen abstraction from phenolic hydroxyl groups (equation 5) in Figure 16.6 [58],... 

The majority of PCB photodegradation studies have been carried out in solution with organic or combined solvents preferred due to their low water solubility. Reductive dechlorination is the predominant photodegradation pathway in hydrocarbon solvents as well as alcohols. In aqueous media and alcohols photonucleophi 1 ic displacement reactions yielding phenols or alkoxy derivatives, respectively, also are detected. In the gas phase PCB are photochemically converted to hydroxylated derivatives (26). Photochemical reduction also is the major reaction pathway in thin films (7), solid phase (8) and on silica gel surfaces (9). 

We examine here a number of reaction pathways for nitric oxide, with the emphasis on assessing their biological relevance. To date, the fastest reaction for nitric oxide with clear toxicological significance is that with superoxide to produce ONOO" (Huie and Padmaja, 1993). Thus, the chemistry and reactivity of ONOO" are discussed at length. In addition, the interaction between ONOO" and nitric oxide is examined with respect to its effects on nitric oxide half-life as well as effects on peroxynitrite reactivity toward phenol. Reaction mechanisms are proposed to account for the nitrated, hydroxylated, and nitrosated phenolic products seen. 

Scheme 2. Reaction pathway for dihydroxybcnzenc in phenol hydroxylation over hydrotalcites...

The effect of incorporating tin into titanium sUicahte-1 (TS-1) on the kinetics of phenol hydroxylation to dihydroxybenzenes with aqueous hydrogen peroxide has been investigated (197). The pathways are illustrated in Figure 1.9. The hydroxylation reaction was modeled using the results obtained with a batch reactor, whereby mass transfer Hmitations were carefully excluded. The analysis of the kinetics indicated that under the same reaction conditions, titanium-tin sUicalite-l (Ti—Sn-S-1) gave a h her phenol conversion rate than TS-1. This difference was attributed to the presence of active tin sites. The incorporation of tin influences the initiation of... 

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