Influence of Hexasulfonated Calix[6]arenes on the Reactivities of Arenediazonium Ions in an Aqueous System

The pKa of Phenol Blue shifted from 4.6 to 6.2 because of complexation of protonated Phenol Blue in the cavity of hexasulfonated calix[6]arene with dodecyl substituents (2C12). The finding stimulated us to examine whether the analogs (2C) suppress the dediazoniation of arenediazonium ions in an aqueous system as crown ethers do in organic solvents. We have found that 2C can suppress the dediazoniation in an aqueous system where neither 18-crown-6 nor anionic micelles are effective. The magnitude of the inhibition effect was 4–5 fold. The reaction rate of the diazo coupling with N,N-dimethylaniline was significantly suppressed in the presence of 2C, suggesting that arenediazonium ions are deactivated through complexation with 2C. The novel stabilization effects were explained by the strong anionic reaction field which neither 18-crown-6 nor anionic micelles have: that is, 2C has a peculiar architecture that six sulfonato groups are circularly arranged on the edge of the calixarene cavity.