Hydroquinol, formation

Before the advent of slippage, the formation of [2]rotaxanes included a very limited array of choices for the macrocyclic bead and the rod. In essence, the use of macrocyclic polyethers, like BPP34C10 as the bead component, is only beneficial if there is a mutual recognition between the 7C-electron rich hydroquinol rings contained within the crown and a 7i-electron poor site on the dumbbell component. This route was limiting in that it requires two 4,4-bipyridinium dications to be present in order that one BPP34C10 ring can be incorporated into the assembly Scheme 10). 

The formation of DPQ not only reduces the yield of polymer but also degrades its quality. Thus, it is imporant to remove both the DPQ and metallic catalyst residues from the reaction solution because they could result in discoloration and degradation of resin while processing. In typical large scale operations, the reaction mixtures are usually treated with a combination of the dihydric phenol and a mild reducing agent, e.g. hydroquinol and sodium sulfite for 20-30 minutes to minimize the residues before isolation of the polymer (Figure 2.2.). 

Figure 10 (A) The ion pair I N R4 [R = (CH2) Mej. An increase of n causes an increase of the separation distance and a decrease of AF of formation. (From Ref. 44. Copyright 1988 Am. Chem. Soc.) (B) Dipol-dipol interaction parameters for H-bonds. (C) Induced dipoles. AF for ion pair formation increases not only with the number of salt bridges but also with the number of aromatic rings in a series of di- and trications and di- and Irianions. (From Ref. 36.) (D) n-n stacking interaction plus H-bonds contribute to the stabilization of a complex between paraquat [PQT] + and a cyclophane-Uke macrocycUc polyether with hydroquinol rings. (From Ref. 12. Copyright 1997 Am. Chem. Soc.)...

---