Employing supramolecular chemistry strategies for the separation of mixtures of anisole and bromoanisole isomers

In the present work, host compounds trans-9,10-dihydro-9,10-ethanoanthracene-11,12-dicarboxylate (H1), trans-α,α,α’,α’-tetraphenyl-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol (H2) and trans-α,α,α’,α’-tetra(p-chlorophenyl)-9,10-dihydro-9,10-ethanoanthracene-11,12-dimethanol (H3) were assessed for their host ability for anisole (ANI) and 2-, 3- and 4-bromoanisole (2-, 3- and 4-BA). It was demonstrated that H3 formed complexes with each of these guest species, while H1 and H2 only possessed the ability to enclathrate ANI. When H3 was crystallized from equimolar binary guest solutions, a significantly enhanced host affinity was observed for ANI and 3-BA. As examples, equimolar binary ANI/2-BA and 2-BA/3-BA solutions afforded complexes that demonstrated a near-complete H3 selectivity towards ANI (97.5%) and 3-BA (94.5%), respectively. Furthermore, from H3 crystallization experiments in binary ANI/2-BA, ANI/4-BA, 3-BA/2-BA and 3-BA/4-BA mixtures, where the molar guest amounts were varied sequentially, were calculated significant selectivity coefficients (K values), so much so that H3 may be used to separate very many of the guest anisole mixtures prepared in this work, through supramolecular chemistry strategies, which serves as a greener separation protocol compared with tedious and energy intensive fractional distillations. Thermal analyses were also used to investigate the relative stabilities of each of the single solvent complexes.