Preliminary design of learning material on Kolbeschmitt reaction mechanism visualized by crystal data

Abstract

In order to educate introductory chemistry, both imagining and visualizing the structures of molecules and complex ions have been  considered to be of significance for learners. Some of sodium phenoxide (NaOPh), common compound in organic chemistry as a reactant  of the well-known industrial process, ‘Kolbe-Schmitt reaction’, have unique crystal structures including square units consisting  like “cubane” form. Sodium salicylate is a product of the reaction, and its crystal structure was reported recently. However, this fact is  seemed to be almost unknown in chemical education. Therefore, I report a study herein about the possibility of crystal structural data  available in the Cambridge Crystallographic Data Centre (CCDC) as potential learning material in chemical education. Consequent  searched some crystal structures; it was found that pure NaOPh crystal has rigid polymer chain structures involving four-membered  square Na₂O₂ unit. On the other hand, others have structures with one or several crown ethers or solvent molecules. The crystals of  NaOPh coordinated by several solvent molecules are indicating as if they are in the dynamic reacting process with solvation, in spite of  that they indeed are in solid state. Regrettably, there seemed no exact crystal data of NaOPh solvated with CO₂ itself. Instead, combined  with the crystal structure of the product, i.e., sodium salicylate, a reaction mechanism could be speculated. When teaching chemistry,  these crystallographic data would be effective enough to explain the dynamic reacting process of the Kolbe-Schmitt reaction for students  with their impression.