Cation-pool technique

A report has described a route to multiply alkylated thiophene derivatives from electrochemically derived diarylcarbenium ions (Scheme 46). Using the cation-pool technique - in which the cationic intermediate is generated in high concentration and pooled - the carbocation (228) alkylates thiophene, providing up to 58% of the trialkylated product (229) and 24% of the dialkylated product (230). 

A low-temperature electrochemical oxidation system for the generation of cation pools is shown in Figure 5.6. The DC power supply is not very expensive, and the reactions can be easily conducted with normal laboratory techniques that are used for the handling of air-sensitive reagents at low temperatures. 

Self-diffusion measurements using the NMR technique have also elucidated the matter of water structure in the pool up to 10-15 water molecules per — 03 group (when AOT is the surfactant) were shown to be structurally perturbed [42]. From self-diffusion NMR studies of AOT-induced w/o microemulsions, Maitra proposed several regions of bound water in the water pool domain [43]. The state of water in the pool for cationic surfactant-containing microemulsions (water/dodecyidimethyl ammonium bromide or didodecyldimethyl ammonium bromide/chloroform or cyclohexane) was examined by NMR self-diffusion studies at different [Fl20]/[amphiphile] ratios or rvalues. Three types of water molecules— bound, aggregated, and free—in various proportions have been envisaged [44]. 

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