Voltammetric Studies of Paracetamol with Some Functional Amines at Different pH Media

Abstract

Electroactive paracetamol adducts such as paracetamol-diethylamine and paracetamol-diisopropylamine were synthesized electrochemically. The products has been studied by Cyclic voltammetry (CV), Controlled potential coulometry (CPC), Differential pulse voltammetry (DPV) and Chronoamperometry (CA) techniques using Glassy carbon (GC), Gold (Au) and Platinum (Pt) electrodes. The studies have been carried out in variation of paracetamol, diethylamine and diisopropylamine concentration, buffer solution of different pH, different electrodes and scan rate. After the insertion of diethylamine and diisopropylamine in paracetamol solution at the second scan of CV potential, new anodic and cathodic peaks appeared at the negative potential. In the presence of nucleophiles with paracetamol as Michael acceptors the oxidation and reduction peak shifted with respect of pure paracetamol. Also the anodic and cathodic peak current changes significantly compared with the pure paracetamol that indicates the participation of reaction of p-quinoneimine with diethylamine and diisopropylamine. The products generated from the reaction of paracetamol with diethylamine and diisopropylamine are assumed to be N-(3-(diethylamino)4- hydroxyphenyl)acetamide and N-(3-(diisopropylamino)-4-hydroxyphenyl)acetamide respectively that undergo electron transfer at more negative potentials than the paracetamol. The influence of pH of paracetamol in presence of diethylamine and diisopropylamine was studied by varying pH from 3 to 9. For diethylamine and diisopropylamine, it is observed that at pH 3-5, no new anodic peak appeared after monotonous cycling. In the pH 7, the pdienone endures nucleophilic attack by the amines that voltammetric new anodic peaks A1 and A2 appeared after monotonous cycling. Whereas in pH 9, the voltammogram display a new peak at the first scan of potential. In lieu of diethylamine and diisopropylamine, the maximum peak current is observed at pH 7. The slopes of the peak potential, E vs pH plot was determined graphically as the anodic peaks of paracetamol-diethylamine (37 mV/pH for first anodic peak A3) and paracetamol-diisopropylamine (23 mV/pH for first anodic peak A3) at 0.1V/s in the cycle. This ascribed that the oxidation reaction of paracetamol-diethylamine and paracetamol-diisopropylamine adducts proceeded via the 2ei2H process. This also indicates that during the reaction not only electron but also proton are released from the paracetamol-amine adduct. The reaction was strongly influenced by the pH as well as concentration of diethylamine and diisopropylamine. The reaction was mostly favorable in 150mM of diethylamine and 150mM of diisopropylamine with fixed 2mM of paracetamol at pH 7. The electrochemical reaction of paracetamol-diethylamine and paracetamol-diisopropylamine adduct are facilitated in neutral media. The effect of scan rate on cyclic voltammogram of paracetamol in presence of diethylamine and diisopropylamine were also investigated. The peak currents of both the anodic and the corresponding cathodic peaks increase with the increase of scan rate. The nearly proportionality of the anodic and corresponding cathodic peak ascribes that the peak current of the reactant at each redox reaction is controlled by diffusion process. The current function, I1,/v"2 of paracetamol-amine derivatives were found to be decreased exponentially with increasing scan rate. In all the studies of paracetamol-amine derivatives have been found to undergo electrochemical reaction with ECE (electron transfer-chemical reaction- electron transfer) type mechanism. Controlled-potential coulometry was studied of catechol in presence of diethylamine and diisopropylamine. During the course of coulometry, the appeared peaks height increase proportionally to the advancement of coulometry, parallel to the decrease in the height of paracetamol peak. These observations also indicate the participation of reaction of paracetamol with the studied nucleophiles. The electro-synthesized products originated from the bulk electrolysis of paracetamol with diethylamine and diisopropylamine were isolated. The formations of new products were also ascertained by FTIR spectra.