Acid–base properties of sulfur-bridged calix[4]arenesElectronic supplementary information (ESI) available: raw data and determined experimental parameters for the potentio- and photo-metric titrations; A–, AD–, ADQ–diagrams of 3. See http://www.rsc.org/suppdata/p2/b2/b200228k/
- 9 May 2002
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 2
- No. 6,p. 1166-1172
- https://doi.org/10.1039/b200228k
Abstract
The acid–base properties of sulfur-bridged calixarenes, thiacalix[4]arenetetrasulfonate (4) and its sulfonyl analogue (5), have been investigated via potentio- and spectrophoto-metric studies, comparing them with the conventional methylene-bridged calix[4]arenetetrasulfonate (3). The titration curves revealed the acidity of the phenolic OH groups in the calix[4]arenes 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 calix[4]arene; 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 calix[4]arenes 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.Keywords
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