Electrochemical Study Of 4-(2- amino-1-hydroxyethyl)benzene-1,2-diol in the Presence of Triethyl phosphite

4-(2-amino-1-hydroxyethyl)benzene-1,2-diol also called Norepinephrine (NEP) is a catecholamine with multiple roles including those as a hormone and a neurotransmitter.[1] It is the hormone and neurotransmitter most responsible for vigilant concentration in contrast to its most chemically similar hormone, dopamine, which is most responsible for cognitive alertness.[2] The mechanism of electrochemical oxidation of NEP, in the presence of triethyl phosphite as a nucleophile has been studied in an aqueous solution using cyclic voltammetry and controlled potential coulometry. Cyclic voltammetry was performed using a Behpajoh Model BHP 2061-C potentiostat/galvanostat. In the voltammetry experiments, a glassy carbon disc (2 mm diameter) and a platinum wire were used as working and counter electrodes, respectively. The working electrode potentials were measured versus Ag/AgCl (KCl 3.0 M). All electrodes were purchased from AZAR electrode. Alumina powder (0.3 M) was used for mechanical polishing of the working electrode. This treatment was followed by ultrasonic cleaning for 30 s. Figure show the CVs of 1.0 mM solution of NEP in the pH 6.0 and 7.0. The CV in the pH=6 show one anodic peak (A1) related to the conversion of the catechol moiety of NEP to o-quinone and one cathodic peak (C1) related to the reduction of the produced o-quinone under mild acidic conditions. At pH =7.0, the CV show one anodic peak in the positive-going scan and two cathodic peaks (C2 and C3) in the negative-going scan. In the second cycle, the CV show another anodic peak, A2, as the counterpart of C2. The appearance of these new anodic and cathodic peaks indicates the formation of an electroactive species at this condition. The most probable reaction for the formation of this product is the intramolecular Michael addition of amine group to electrochemically generated o-quinone. More voltammetric studies were performed at various scan rates and the normalized voltammograms of NEP. a Normalized CVs are obtaind by dividing the current of CVs by the square root of the scan rate. They can be simply overlaid for obtaining more useful information. [3] 126 The reaction mechanism is an ECE mechanism and the products of reaction are believed to be triethyl phosphite derivatives of NEP. The whole characteristics of a typical ECE mechanism are observed for this electrode reaction in which E represents an electron transfer at the electrode surface and C represents a homogeneous chemical reaction. The observed homogeneous rate constants (kobs) for reactions were estimated by comparing the experimental voltammetric responses with the digitally simulated results based on the proposed mechanism. The simulated cyclic voltammograms show good agreement with those obtained experimentally. A quantitative relation between half-wave potentials of NEP and the reactivities of their corresponding o-Quinone were derived.