The acid-base properties of sulfur-bridged calixarenes, thiacalixarenetetrasulfonate (4) and its sulfonyl analogue (5), have been investigated via potentio- and spectrophoto-metric studies, comparing them with the conventional methylene-bridged calixarenetetrasulfonate (3). The titration curves revealed the acidity of the phenolic OH groups in the calixarenes 3-5 to be in the order: 3 < 4 ≪ 5. In particular, the oxidation of the bridging sulfur to sulfone strongly enhanced the acidity of the sulfur-bridged calixarene; the pKa,n values (n = 2-4) of the sulfone-bridged 5 were lower by 7 pK units than those of the sulfide-bridged 4. The effects of the linkage groups on the acidity of the calixarenes are discussed from the structural and electronic viewpoints, such as the macrocyclic ring size, the hydrogen bonding manner, and the resonance of the linkage moiety.
|Number of pages||7|
|Journal||Journal of the Chemical Society, Perkin Transactions 2|
|Publication status||Published - 2002|