Transport of Neutral Arenes through an Aqueous Barrier by Resorcinol–Aldehyde Tetramers

The transportation of neutral arenes such as benzene, toluene, o,m,p-xylene, durene,biphenyl, anthracene and phenanthrene through an aqueous medium using the crownconformation of tetrameric cyclophane hosts 1 and 2 has been studied. In general,transportation of all arenes increases with time, exceptfor toluene, which showssaturation behaviour with both hosts 1 and 2.Among the larger arenes, transportationof biphenyl is a maximum with 1; with host 2,transportation of anthracene is a maximumdue to its larger association constant. In the case ofsmaller arenes, 1 transportsbenzene most effectively, and transportation decreases asthe number of methyl groups onbenzene increases, showing that stereoelectronic factors affecttransportation. With 2toluene is transported most effectively due tothe change in the shape of the binding cavitycaused by a change in bridging groups. A comparison oftransportation for 1 h with 1 and 2shows that for all arenes transportation is greater withhost 2 than with 1 due to thehydrophobic nature of 2.