(57a) Investigation into a Novel, Green Technology for Aromatic Thiol Production, a Density Functional Theory (Dft) Study

Aromatic thiol synthesis is an industrially important petrochemical process. Thiols are precursors for the production of herbicides, dyes, pharmaceuticals and a host of other profitable compounds. A new technology has been developed to synthesize 2,5-dimethylbenzenethiol from 2,5-dimethylbenzene sulfonyl chloride. This new technology eliminates harmful by-products and brings the process more into line with the tenets of Green Chemistry. In this study, the technology was investigated using ab initio, density functional theory (DFT) calculations to calculate energies of adsorption to the palladium on carbon (Pd/C) catalyst and to simulate transition state structures for the rate controlling step of the reaction. The steps taken to achieve these goals include: 1) designing suitable Pd catalyst model matrices to incorporate ease of calculation and accurate simulations, 2) testing multiple modes of adsorption for the primary reactant molecule, 3) calculating the minimum energy and configuration of the adsorbed reactant structures with and without the presence of hydrogen molecules (the secondary reactant), and 4) evaluating the results of the transition state simulations. The calculated adsorption energies were in the range of -51 to -57 kcal/mol, and were similar for equivalent adsorption modes over different catalyst matrices. The results are within the expected range as indicated by calculated adsorption energies on individual atoms of chlorine and oxygen adsorbed to palladium, Cl approximately -77 kcal/mol and O approximately -25 kcal/mol. [1,2] Some possible transition state structures have been calculated, but confirmation of these structures is still pending. Once confirmed, reaction energies and reaction pathways can be determined and compared with experimental data. When agreement between the experimental and theoretical adsorption energies is achieved, advances in the knowledge of an industrially important reaction are attained.

[1] Dominic R. Alfonso, Anthony V. Cugini, David S. Sholl, Surface Science 546 (2003) 12-26.

[2] K. H¸jrup Hansen, Þ. Ðljivanèanin, E. Lzgsgaard, F. Besenbacher, I. Stensgaard, Surface Science 505 (2002) 25-38.