Abstract
The title salt, C(8)H(20)N(+)·C(22)H(27)O(3)S(-), is a proton-transfer compound derived from the recently reported parent carb-oxy-lic acid [Alhadi et al. (2010). Acta Cryst. E66, o1787] by the addition of a second equivalent of di-n-butyl-amine, yielding the di-n-butyl-ammonium carboxyl-ate salt. The structure of the carboxyl-ate anion resembles that of the parent carb-oxy-lic acid. The main difference lies in the position of the H atom in the 4-hy-droxy group. In the anion the O-H bond is perpendicular, rather than parallel, to the benzyl ring. This position appears to facilitate hydrogen bonding to an O atom of the carboxyl-ate group of a symmetry-related anion. In addition, there are three N-H⋯O hydrogen bonds. In contrast, the neutral species hydrogen bonds via a carboxylic acid dimer. The dihedral angle between the benzene rings in the anion is 79.19 (7)°.