Interaction of Dextroamphetamine Sulfate with Dextrates in Solution

Abstract

The interaction between dextroamphetamine sulfate and dextrates (a partially hydrolyzed starch composed of 92% dextrose combined with 8% higher saccharides) was studied in buffered solutions at three different temperatures and dextroamphetamine sulfate concentrations. On heating, solutions containing dextroamphetamine sulfate and dextrates became progressively darker than solutions containing dextroamphetamine sulfate or dextrates alone. Also, a new absorption maximum appeared at 298nm. in the solutions containing dextroamphetamine sulfate and dextrates. The rate of browning in these solutions increased with increasing temperature and pH and decreased with increasing dextroamphetamine sulfate concentration. From the relationship shown in the plots of absorbance against time, the browning reaction was assumed to follow an apparent zero-order rate law and the rate constants, k, were calculated for all solutions containing dextroamphetamine sulfate and dextrates at pH 6 and 8 at 50, 60, and 70°. Arrhenius-type plots were also obtained and were used to approximate the browning rate at 25°. By using TLC, IR spectroscopy, and elemental analysis, the brown material isolated from the discolored solutions was identified as amphetamine-hydroxymethylfurfural. A Schiff base-type reaction was postulated involving the primary amine and the carbonyl groups of the sugar.