Investigation of the host ability and selectivity of the wheel-and-axle compound, 1,4‑bis(diphenylhydroxymethyl)benzene, in pyridines and mixed pyridines Jarryd Vorgers, Benita Barton, Dr Eric Hosten Nelson Mandela University, South Africa The aim of this investigation was to determine whether the wheel-and-axle host compound, 1,4‑bis(diphenylhydroxymethyl)benzene ( H ), may be employed effectively for the separation of mixed pyridines through supramolecular chemistry strategies. The more usual fractional distillations are extremely tedious, time- consuming, costly and oftentimes not adequately efficient to afford products of high enough purity for further applications owing to their very similar boiling points. The pyridines that were considered are 2-methylpyridine (2MP, b.p. 129 °C), 3-methylpyridine (3MP, b.p. 144 °C), and 4‑methylpyridine (4MP, b.p. 145 °C), while pyridine (PYR, b.p. 116 °C) was also added for the sake of completeness. These pyridines often present as mixtures during their syntheses and subsequent separations are then challenging. Single-solvent crystallization experiments demonstrated that H has the ability to form a complex with each of the four guest solvents, all with 1:2 host:guest ratios. Crystallization experiments of H in both equimolar and binary non-equimolar mixtures of these guests showed the host compound to have an overwhelming preference for both PYR and 4MP in certain conditions, alluding to the possibility that H would be able to serve as a highly proficient alternative separatory tool for many of the mixtures that were prepared in this work. Single crystal X-ray diffraction experiments revealed the reasons for these host selectivity observations: only PYR and 4MP experienced significant π···π interactions with another guest molecule, and stronger hydrogen bonds between the host compound and these guest species were also noted compared with those complexes containing the less preferred 3MP and 4MP species. Hirshfeld surface analyses, furthermore, demonstrated that PYR and 4MP were also involved in a greater number of (guest) N···H(host) interactions. Finally, thermal analysis was employed in order to obtain the relative thermal stability of each single-solvent complex produced in this work.
P06
© The Author(s), 2023
Made with FlippingBook Learn more on our blog