One-Pot Multicomponent Synthesis of 2H-Chromene Derivative, Kinetics, and Thermodynamic Studies Using a Stopped-Flow Technique in Combination with Theoretical Computation Methods

Abstract

The diethyl 6-bromo-2H-chromene-2,3-dicarboxylate (4) was successfully synthesized by the reaction between triphenylphosphine (1), diethyl acetylenedicarboxylate (DEAD, 2) and 5-bromo-2-hydroxybenzaldehyde acid (3) in the presence of dichloromethane. The 2H-chromene’s compound were characterized using IR, ¹H, ¹³C, and ³¹P NMR spectroscopy. The kinetics and mechanism of the reaction were experimentally investigated by stopped-flow technique and UV–vis spectrophotometry. The first step in the proposed five-step mechanism, the reaction between 1 and 2 for the formation of intermediate 1 (I₁), was fast. The reaction of I₁ and 3 was slow and followed first-order kinetics. The experimental kinetic data proved that the step₄ of the proposed mechanism is a rate-determining step. To make a further understanding about the proposed mechanism, theoretical investigations were carried out at the B3LYP/6-31++g(d,p) level of theory. The calculations showed that the step4 (Δ$H_{4\mathrm{ }\left(\text{DEAD}\right)}^0=$ 82.1 kJ/mol) is in terms of energy undesirable and difficult in line with experimental results, and is an endothermic process. It also cleared that why I₃ with diethyl groups in step₄ tends to convert to the I₄ very slowly through a four-member ring formation in comparison with other steps and ultimately it becomes impossible process (step₄) when t-But groups are replaced instead of diethyl groups within the structure of I₃. The experimental and theoretical data indicated that the overall reaction rate follows second-order kinetics and depends on the concentrations of compounds 1 and 2.

Keywords:

• Kinetics
• stopped-flow
• triphenylphosphine
• 2H-chromene derivative

Acknowledgments

This work was supported by the University of Sistan and Baluchestan.