Alkyl chain length and metallic cation effects on the acid-base properties of C-alkylresorcin[4]arenes in aqueous media

SALAS, SANTIAGO D.; BAUMGARTNER, MARÍA T.; VEGLIA, ALICIA V.

JOURNAL OF MOLECULAR LIQUIDS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2019 vol. 277 p. 769 - 775

0167-7322

The polyprotic behavior of C-alkylresorcin[4]arenes was investigated in aqueous media in a large interval of pHvalues by potentiometry and spectrophotometry. The pKa1; pKa2; pKa3 and pKa4were determined. The pKai valuesdetermined by both methods correlate very well.The influence of the alkylic chain length on the bridge carbon of the resorcin[4]arene were determined for Cmethylresorcin[4]arene (C1RA); C-butylresorcin[4]arene (C4RA) and C-heptylresorcin[4]arene (C7RA). This effectwas observed in the lower pKa1 determined for C7RA (2.3) respect to the similar values determined for theothers resorcin[4]arenes (3.2) and an increase in the values of the pKa3 as the length of the alkyl chain is longer(8.3; 9.9; 10.5) without influence on pKa2 (6.9) and pKa4 (10.4).Also, the influence of the metallic cation of the base (Li+, Na+ or K+)was determined on the acid-base constantsof C4RA. The values for the first and four dissociation constants are practically the same without influence of thecounter ion of the base (pKa1=3.1 and pKa4=10.5); but the influence of Li+ is observed as a higher pKa2 (7.7)and a lower pKa3 (9.0) than with Na+ and K+ (pKa2 = 7.0 and pKa3=9.8).These effects were interpreted on the basis of the ditopic characteristic of the resorcin[4]arenes, the interaction/complexation of the solvate of each cation with the acid-base specie of each macrocycle and their stabilization.