O-Quinonic formation

Refiner mech. pulp o-Quinones Formation of oxyphosphorane adduct 10-12 Lebo et al. 1988... 

The kinetic curve of the changes in the ozone concentration at the bubbling reactor outlet (Fig. 10) is characterized by three different regions AB - fast ozone consumption after the addition of pyrocatechol, BC -steady-state part, when the rate of the chemical reaction becomes equal to the rate of ozone supply, and CD - the ozone concentration begins to rise up due to the p Tocatechol consumption. The BC part of the curve allows calculation of the rate constant, and based on the area below the curve ABCD - evaluation of the stoichiometry of the reaction. The straight line designated [03] is the ozone concentration at the reactor inlet. Curve 2 presents the o-quinone formation in the course of the reaction time. Its profile suggests the intermediate formation of o-quinone. 

The kinetic curves of the product formation in pyrocatechol ozon-olysis, its consumption and o-quinone consumption during its ozonation in a separate experiment are given in Fig. 11. The rate constants of pyrocatechol and o-quinone consumption, calculated based on the kinetic curves in Fig. 11, were 3.2 x 10 M. s and 7.1 x 10 M . s , respectively. The initial rate of the o-quinone formation had almost the same value as that of pyrocatechol consumption. The small variation of the constants is due to the participation of pyrocatechol in parallel reactions. Actually, during the reaction small amounts of open-chain products have been identified. 

The mechanism of the thermal o-QHP decay involves two consecutive reactions. The primary step is the breaking of the 0-0 bond, and the resulting cyclohexadienone alkoxy radical is capable of dissociating with o-quinone formation ... 

Unexpectedly, a completely different reaction took place in the oxidation of 2-(l-propenyl)phenol (111) with PdCh. Carpanone (112) was obtained in one step in 62% crude yield. This remarkable reaction is explained by the formation of o-quinone, followed by the radical coupling of the side-chain. Then the intramolecular cycloaddition takes place to form carpanone[131]. 

The use of ultrasonic (US) radiation (typical range 20 to 850 kHz) to accelerate Diels-Alder reactions is undergoing continuous expansion. There is a parallelism between the ultrasonic and high pressure-assisted reactions. Ultrasonic radiations induce cavitation, that is, the formation and the collapse of microbubbles inside the liquid phase which is accompanied by the local generation of high temperature and high pressure [29]. Snyder and coworkers [30] published the first ultrasound-assisted Diels-Alder reactions that involved the cycloadditions of o-quinone 37 with appropriate dienes 38 to synthesize abietanoid diterpenes A-C (Scheme 4.7) isolated from the traditional Chinese medicine, Dan Shen, prepared from the roots of Salvia miltiorrhiza Bunge. 

Iodine addition to the ter- [13] tiary nitrogen of the opium alkaloids and to the OCH3 group of the brucine with formation of an o-quinone derivative, probably ring opening in the case of phenylbutazone, ketazone and trimethazone detection by IR... 

Foster, K. L. Baker, S. Brousmiche, D. W. Wan, P. o-Quinone methide formation from excited state intramolecular proton transfer (ESIPT) in an o-hydroxystyrene. J. Photochem. Photobiol. A Chem. 1999, 129, 157-163. 

In a similar approach, double deprotonation of r 6-coordinated ortho- and para-cresols, 30 and 31, with t-BuOK led to formation of stable r 4-coordinated p- and o-quinone methide complexes of manganese, 32 and 33 (Scheme 3.19).37... 

Stokes, S. M. J. Ding, F. Smith, R L. Keane, J. M. Kopach, M. E. Jervis, R. Sabat, M. Harman, W. D. Formation of o-quinone methides from T 2-coordinated phenols and their controlled release from a transition metal to generate chromans. Organometallics 2003,22, 4170-4171. 

Wang, J. Pettus, L. H. Pettus, T. R. R. Cycloadditions of o-quinone dimethides with p-quinol derivatives regiocontrolled formation of anthracyclic ring systems. Tetrahedron Lett. 2004, 45, 1793-1796. 

Quercetin is a naturally occurring flavonoid with both antioxidant and prooxidant activities (Scheme 10.12).90 It has been demonstrated in a variety of bacterial and mammalian mutagenicity experiments that quercetin has mutagenic properties that could be related to quinoid formation.91,92 Quercetin is initially oxidized to an o-quinone, which rapidly isomerizes to di-QMs that could also be called extended... 

Attempts of further nitration of dinitro derivative 83 under usual conditions failed. Using 100% nitric acid in fluorosulfonic acid or trifluoromethanesulfonic acid, reagents useful for nitration of deactivated aromatic systems led to the formation of moisture-sensitive nitration products, which undergo further oxidation to give o-quinone-like species 84 and 85. Using the latter conditions, compound 86 can be isolated in 20% yield and converted into the tetraoxo derivative 85 by heating at 220°C (Scheme 4) <1996JOC1898>. 

The nitration of the polyheterocyclic compound 226 leads to the formation of moisture-sensitive nitration products, which undergo further oxidation to give o-quinone-like species (Scheme 55) <1996JOG1898>. 

In order to explain the formation of the product 9 during oxidation at two different potentials we have performed the experiments with cyclic voltammetry [45]. The cyclic voltammogram of catechol (QH2) exhibits the anodic wave at 0.25 V vs SCE (Fig. la) corresponding to the formation of o-quinone (Q) which is reduced in the cathodic sweep at 0.05 V vs SCE. The cathodic counterpart of the anodic peak disappears, when a sufficient amount of 4-hydroxycoumarin was added, and a second irreversible peak at 0.95 V vs SCE appeared (Fig. lb). 

The anodic oxidation of catechol in the presence of 1,3-dimethylbarbituric acid was carried out in aqueous solution containing sodium acetate in an undivided cell at graphite and nickel hydroxide electrodes [114]. The results did not fit with the expected structure (Scheme 47, path A) but a dis-piropyrimidine was isolated in 35% yield (Scheme 47, path B). It seems that the initial attack of 1,3-dimethylbarbituric acid on the anodically formed o-quinone does not occur through the carbon-oxygen bond formation but rather through the carbon-carbon bond formation, giving rise to the final product via several consecutive reaction steps. 

Ozonization of phenol in water resulted in the formation of many oxidation products. The identified products in the order of degradation are catechol, hydroquinone, o-quinone, cis,ds-muconic acid, maleic (or fumaric) and oxalic acids (Eisenhauer, 1968). In addition, glyoxylic, formic, and acetic acids also were reported as ozonization products prior to oxidation to carbon dioxide (Kuo et al, 1977). Ozonation of an aqueous solution of phenol subjected to UV light (120-W low pressure mercury lamp) gave glyoxal, glyoxylic, oxalic, and formic acids as major products. Minor products included catechol, hydroquinone, muconic, fumaric, and maleic acids (Takahashi, 1990). Wet oxidation of phenol at 320 °C yielded formic and acetic acids (Randall and Knopp, 1980). 

Benzofuroxans can be prepared by oxidation of o-quinone dioximes with, for example, fer-ricyanide or hypohalite in a process which closely parallels the formation of monocychc furoxans from glyoximes. Its utility is restricted by the availability of the starting materials which are themselves often best made by reduction of the furoxan. However, it is a valuable approach when the parent quinone or its monooxime is accessible by other means. It was, for example, the route originally used for naphtho[l,2-c]furoxan, the first aromatic-fused derivative <1886CB176>, and it is the method of choice for acenaphthofuroxans (11). In other cases oxidation of o-nitroanilines or thermolysis of o-nitroaryl azides are more suitable. 

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