Coupling Interaction of Ampicillin Drug with Ninhydrin in Aqueous Acidic Medium: Kinetics and Mechanistic Studies

The Kinetics of Ninhydrin (Nin) reaction with Ampicillin (Amp) has been studied in an aqueous acidic medium. The product of the reaction was examined spectroscopically using Nuclear magnetic resonance (1H-NMR) and Infrared spectra in addition to Ultra-performance liquid chromatography (UPLC). The reaction was monitored spectrophotometrically, with (0.1- 0.4) × 10-4 mol dm-3 of Amp, (0.5-5.0) ×10-2 mol dm-3 Nin and 0.3- 0.9 mol dm-3 ionic strength (I) over the (30-50) °C range of temperature. It is first order with respect to [Nin] and [Amp], decreases as pH increases in the range (4.70 -6.04). The effect of the catalyst on the rate of the reaction was studied. The thermodynamics activation parameters involving ∆H* and ∆S* have been calculated. The rate of the reaction follows the rate law d[Amp-Nin]/dt ={k2 + (k4+k3[H+])[Nin]}×[ Amp]. For this reaction is proposed mechanism was supported by an excellent isokinetic relationship between ∆H* and ∆S* for some Nin reactions. In emergency case when posing with Amp about 30% of the oral dose is excreted in urine in 6 hours as unchanged drug, so a presumptive colour test is necessary in clinical toxicology. Then, using Nin to form a coupling complex with Amp is an effective method.