Experimental and Computational Studies on the 1:1 Complex of Anthranilic Acid with P-Toluenesulfonic Acid

Abstract

The proton-transfer compound (3) was synthesized in good yields by the reaction of anthranilic acid with p-toluenesulfonic acid. It was characterized by elemental analysis, infrared spectroscopy, and X-ray single-crystal determination. The crystal structure analysis of 2-carboxyanilinium p-toulenesulfonate (3) has revealed a one-dimensional hydrogen-bonded network structure, involving the tosylate anion, the carboxyl group, and the ammonium group. The H(N)···O distances range from 1.97 to 2.23 Å. The molecular geometry and vibrational frequencies of 3 were calculated using the ab-initio method (HF) with the 6–31G(d) and 6–31+G(d,p) basis sets. The computed results indicate that the optimized geometry reproduces the crystal structure well, and the assignments of fundamental vibrations also agree well with the theoretical frequencies. The intermolecular proton transfer process between the ionic (3) and nonionic (4) structures was also investigated with the theoretical computations. The nonionic form (4) is energetically more stable than the ionic form (3) and TS(3→4) by 9.76 and 7.01 kcal/mol, respectively, including the zero-point vibrational energy correction at the HF/6–31+G(d,p) level. In addition, the atomic charges, the molecular electrostatic potentials, the nucleus-independent chemical shifts, and the frontier molecular orbitals of 3 were carried out at the HF/6–31+G(d,p) level of theory.

Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional figures and tables

GRAPHICAL ABSTRACT

Keywords:

• Proton transfer compound
• FTIR spectra
• crystal structure
• Hartree–Fock method
• NICS analysis

Acknowledgments

The authors are indebted to the Scientific and Technical Research Council of Turkey (TUBITAK) and University of Balikesir for their financial support. Dr. Kara would like to thank TUBITAK for NATO-B1 and the Royal Society short visit fellowship for financial support and Prof. Guy Orpen (School of Chemistry, University of Bristol, UK) for his hospitality. The authors are also very grateful to Dr. Mairi F. Haddow (The School of Chemistry, University of Bristol) for the X-ray measurements.