LAUSR

Abstract In order to explore the role of glycerol in the Skraup reaction, in producing complex structure quinolines, synthesis of some quinoline-5-carboxylic acid glycerol esters from the commercially available anilines (3-aminobenzoic acid derivatives) has been carried out using a slightly modified Skraup reaction. It has been found that the reaction of an excess of glycerol with 3-aminobenzoic acid with I2 as oxidant in concentrated H2SO4, results in the formation of two acyclic isomers (a, b) of the corresponding glycerol ester, one of them (a) is predominant and a third cyclic isomer (c) obtained in the form of traces. Among the final products, isomer (a) has been purified by flash chromatography and analyzed by IR, 1H NMR, 13C NMR and Mass spectroscopy and isomers (b) and (c) (R = OMe, R’ = H) were identified by 1H NMR. While obtaining the acyclic isomers is quite expected, the cyclic isomer (c), which was previously isolated in traces and characterized, failed to be formed again despite various attempts. To support the experimental results, theoretical computations have been carried out at DFT level and using the B3LYP/6-31++G(d,p) method. Calculations of the activation energies corresponding to the transition states of proposed ways to give isomer (c) show that the formation of this isomer is possible. However, this later is probably obtained from the less predominant isomer (b) which is not an energetically favorable product according to the theoretical calculations. This explains the small amount of isomer (c). Furthermore, the regioselectivity of the esterification reaction has been also assessed by conceptual DFT descriptors.