Synthesis of guanidine-based salts with benzoate and citrate counterions for application as thermolatent bases

Abstract

Thermolatent catalyst only become catalytically active once a certain temperature is exceeded. This enables the controlled onset of chemical reactions, such as polymerization and curing reactions or dynamic bond exchange reactions in covalent adaptable networks. Herein, thermally responsive Brønsted base generators (TBGs) are synthetized, designed to undergo thermal cleavage and liberate active bases under controlled heating conditions. All TBGs are obtained in one system from 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) and carboxylate anions derived from orsellinic acid derivatives and citric acid. These anions act as stabilizing agent and are cleaved at defined temperatures liberating TBD in a selective manner. By systematically varying the molecular structure of the acid components, structure–property relationships are elucidated that govern decomposition temperature as well as efficiency of base release. Thermal analysis reveals that the TBGs are stable at room temperature but exhibit controlled decomposition properties between 135 °C and 256 °C, depending on the applied carboxylic acid. Thermal cleavage is found to be selective and irreversible, enabling efficient base release. Measuring pH values in solution confirms that the thermal activation results in a pronounced and reproducible shift in basicity. Consequently, the introduced TBGs are suitable for various applications that require controlled catalytic activation under thermal processing conditions.