The Electrochemical Oxidation of Substituted Catechols

Abstract

The oxidation of substituted catechols was studied by cyclic voltammetry, chronoamperometry, rotating ring‐disk electrode, and coulometry. The results showed that the quinones that were formed from the oxidation of substituted catechols reacted with the basic forms of the starting material to yield the dimeric product. These products were generally unstable and rapidly polymerized or underwent some other irreversible reaction to form an electroinactive product. For 3,4‐dihydroxyacetophenone and propriophenone, the intermediate was stable long enough to be observed in cyclic voltammetry. The rate of the coupling reaction was found to correlate well with the Hammett ρ‐σ parameters and indicated that there was substantial negative charge in the transition state. Finally, an analysis of the coulometric n‐values along with the inormalat1/2/C values indicated that the initial coupling product was a diphenyl ether. Analysis of the coulometry products showed extensive polymerization.

Electrochemical reactions of catechol, methylcatechol and dopamine at tetrahedral amorphous carbon (ta-C) thin film electrodes

“…The hydroxylation reaction has been shown to be quite rapid at high pH because of the abundance of hydroxyl ions that can attach to the o-quinone ring by nucleophilic addition [40]. The observed rate constant for dimerization also increases in more alkaline solutions [42], which could explain why the electron transfer is more adversely inhibited at pH 10.8 than in neutral PBS (both in terms of ΔE p and peak current magnitude as can be seen from Fig. 3).…”

“…It is known that at neutral pH the oxidation of catechol is accompanied by hydroxylation and polymerization reactions. The ortho-quinone can undergo a nucleophilic attack by water to yield a hydroxylated derivative such as a 1,2,4-trihydroxybenzene [40,41] or it can form a dimer with a catechol and polymerize [42]. The shoulder observed after the CA oxidation peak is likely due to the oxidation of one of the products formed in the chemical reactions (no oxidation peak is seen in pure PBS).…”

A New Way for Synthesis of Phenoxazine and Diphenoxazine Derivatives via Electrochemical Method

“…A peak current ratio (I p C1 /I p A1 ) of nearly unity, particularly during the repetitive cycling of potentials may be considered as a criterion for the stability of p-quinone produced at the surface of the electrode under experimental condition. In other words, any hydroxylation [17][18][19][20][21][22] or dimerization [23][24][25] reaction is too slow to be observed on the cyclic voltammetry time-scale.…”

A Green Method for the Electroorganic Synthesis of New 1,3-Indandione Derivatives

“…In other words, any hydroxylation 25,26) or dimerization 27,28) reactions are too slow to be observed on the time scale of the cyclic voltammetry.…”

“…23,24) A peak current ratio (I P A1 /I P C1 ) of nearly unity, particularly during the repetitive potential recycle, can be considered as a criterion for the stability of o-quinone produced on the electrode surface under the experimental conditions. In other words, any hydroxylation 25,26) or dimerization 27,28) reactions are too slow to be observed on the time scale of the cyclic voltammetry.The oxidation of 4-tert-butylcatechol (1a) in the presence of 2-phenyl-1,3-indandione (3) (pK a ϭ4.1) 29) as a nucleophile was studied in detail. Figure 1, CV b presents the cyclic voltammogram obtained for a 0.25 mM solution of 1a in the presence of 0.25 mM 3.…”