Acridine orange as a highly sensitive probe to study the stability of onium salts

Abstract

Halogen and chalcogen bond donors can undergo decomposition in solution, leading to the formation of Lewis acids. When these compounds act as catalysts, an important inquiry emerges: are the observed catalytic effects attributable solely to the parent salts, or do they involve contributions from the resulting decomposition products? Addressing this query necessitates a thorough evaluation of the degree of salt degradation. Conventional analytical methods such as NMR and HPLC, while widely employed for reaction monitoring, often lack sensitivity to detect trace levels of acidic species. In our study, we utilized UV-vis spectrophotometric titrations to assess the stability of halogen and chalcogen bond donor molecules. The findings revealed no discernible relationship between their stability profiles and their catalytic performance. Our data unequivocally support the conclusion that σ-hole carrier-mediated catalysis cannot be categorized as concealed Brønsted-type catalysis.