The electrochemical behaviour of phenol, catechol, hydroquinone, resorcinol,dopamine, and para-substituted phenolic compounds, 4-ethylphenol, tyrosine, andtyramine, was studied over a wide pH range using a glassy carbon electrode. Theoxidation of phenol is pH dependent and irreversible, occurring in one step, andfollowed by hydrolyse in ortho- and para- positions, leading to two oxidation products,catechol and hydroquinone. The oxidation of phenol oxidation products, ortho-phenoland para-phenol, is reversible and pH dependent. The oxidation potential of parasubstitutedphenols varies slightly due to their substituent group in position C4, andoccurs in one oxidation step corresponding to the oxidation of phenol. The oxidationproducts of this group of para-substituted phenols are reversibly oxidised and adsorb onthe electrode surface.
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