Oxidation of pyrocatechol

Experimental observations indicate that the oxidation of cobalt (II) to cobalt (III) and the formation of ethylenediamine from N-hydroxyethylethylene-diamine occur simultaneously. This is quite the opposite to what is usually assumed in other instances of transition metal catalysis of organic reactions—for example, the catalytic effect of manganese in the oxidation of oxalic acid (7, 8), of iron in the oxidation of cysteine to cystine (22) and of thioglycolic acid to dithioglycolic acid (5, 23), of copper in the oxidation of pyrocatechol to quinone and in the oxidation of ascorbic acid (29, 30), and of cobalt in the oxidation of aldehydes and unsaturated hydrocarbons (4). In all these reactions the oxidation of the organic molecule occurs by the abstraction of an electron by the oxidized form of the metal ion. 

Tsuji and coworkers reported that copper(I) chloride in the presence of pyridine, methanol and dioxygen promotes the stoichiometric oxidation of pyrocatechol to methyl muconate.606 Labeling lg02 studies have shown that only one atom of the dioxygen molecule is incorporated in the substrate, while the other one is transformed into water as in enzymic monooxygenases (equation 275)607 (and not as in dioxygenases, viz. pyrocatechase). This reaction has been shown by Rogic et al. to proceed via two steps (equation 276).580,58 ... 

Pospisil, J. and Ettel, V., Oxidation of pyrocatechol to muconic acid, Chem. Prumysl (Czechoslovakia), 7, 244, 1957. 

Oxidation of pyrocatechol. Pyrocatechol (1) is oxidized in the presence of oxygen by KO, in DMSO to the very unstable product 2, characterized by transformation into... 

Figure 11. Lineweaver-Burk plots of the oxidation of pyrocatechol (A), 4-acetylcatechol (B), and 4-formylcatechol (C) by mushroom tyrosinase at several oxygen tensions (102)...

A dissolution of the complex in ethanol (Fig. 2a) and DMF (Fig. 2b) (1 mg/ml) results in its destruction accompanied by oxidation of pyrocatechol and reduction of silver with formation of colloid. Silver particles were adsorbed on the positively charged surface of the substrate. Particle size can be varied between —20 nm in ethanol and -50 nm in DMF. 

Another spectrophotometric flow injection method for the determination of I- and based on the catalytic effect of this ion on the oxidation of pyrocatechol violet by potassium persulphate has been developed. The method allows the determination of 0.5-5 mg/11- at a rate of 60 samples per hour and is subject to very little interference. It was successfully applied to the determination of iodide in table salt (Cerda et al., 1993). 

As the half-wave potential, Ph = 8 for the oxidation of pyrocatechol monoorthophosphate is 1.16 V and that of pyrocatechol is 0.86 V, the polarization curve is displaced towards the cathode side. This is illustrated in Figure 34 showing data on the electrooxidation of pyrocatechol monoorthophosphate on a paste electrode as well as on this electrode modified by alkaline phosphatase. 

An outer-sphere mechanism for the oxidation of pyrocatechol violet by C10 ion in HCl was suggested. The reaction is first order in both oxidant and substrate and follows acid-independent and acid-dependent paths via C10 and HC10 , respectively. The second-order rate constant decreases with increasing ionic strength. ... 

Fig. 7. Rate of oxidation of pyrocatechol (1.0 nM) mushroom PPO in 0.1 sodium phosphate buffer, pH 7.1. The arrow and the S Indicate the time of addition of a new aliquot of substrate (1 Umol).

The kinetics and mechanism of the metal-chelate-catalysed oxidation of pyrocatechols to quinones have been investigated. Comparisons have been made of the base- and Mn ion-catalysed auto-oxidations of 3,5-di-t-butylpyrocatechol (3,5-DTBP) to the corresponding o-quinone (3,5-DTBQ) with the rates when manganese(ii)-4-nitrocatechol, manganese(n)-tetra-bromocatechol and cobalt(n)-4-nitrocatechol (Co -4NQ were present as catalysts. The rates are dependent on hydrogen-ion concentration, and the stoicheiometry and products depend on the nature of the catalytic reagent, viz. 

WOl inhibit the reaction. In contrast, however, WO promotes the decomposition of H2O2 alone. The oxidation of pyrocatechol violet in the presence of amino-acid complexes of copper(n) has been suggested as a means of determining ultramicroquantities of amino-acids e.g. in the presence of glycine the 1 1 complex acts as a catalyst, the pH-dependent reaction in borate buffer obeying the rate law (PV = pyrocatechol violet)... 

The results of the experiments just described provide strong, although indirect, evidence for quinone formation during the conversion of dopamine to norepinephrine and during the conversion of phenylethylamine to phenylethanolamine (in the presence of catechol). The spectral changes which occur during the latter reaction were found (Levin and Kaufman, 1961) to be virtually identical with those reported for the tyrosinase-catalyzed oxidation of pyrocatechol to o-benzoquinone (Mason, 1949) and this result provides direct evidence in favor of the view that Eq. (19) correctly describes the hydroxylation of phenylethylamine in the absence of ascorbate. 

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