Inclusion compounds of hydroxynaphthoic acids: co-crystal vs.salt formation

Abstract

6-Hydroxy-2-naphthoic acid, H1, forms solvates with 1,4-dioxane (DIOX) and dimethyl sulfoxide (DMSO), and their structures are stabilized by host–host and host–guest hydrogen bonds. H1 forms a hydrated salt with 1,4-diazabicyclo[2.2.2]octane, DABCO, with stoichiometry 2H1·2DABCO·3H₂O. Two other naphthoic acid isomers, 1-hydroxy-2-naphthoic acid, H2, and 3-hydroxy-2-naphthoic acid, H3, form salts with DABCO with host : guest ratios of 2 : 1. The kinetics of thermal decomposition of the H1·½DIOX compound yields an activation energy of ∼60 kJ mol⁻¹ for the desolvation reaction.