THERMAL STABILITY OF 1,8-NAPHTHALIMIDE TETRAALKYLAMMONIUM SALTS

Abstract

The synthesis of tetraalkylammonium 1,8-naphthalimides was performed in benzene-5% NaOH aqueous solution at room temperature by anion exchange and subsequent extraction of the desired salts into the organic phase with yields of 93-98 %. It is determined by thermogravimetric analysis that tetraalkylammonium salts of 1,8-naphthalimides are thermally stable to 110-140 °С. Endothermic peaks without mass loss are observed on the thermogravimetric curves of all synthesized salts at a range of 110-140 °С that correspond to the melting points of the salts. The first mass loss is observed at 140-230 °С and is accompanied by endothermic peak at 170-200 °С on DTA curve; complete mass loss is observed at 240-300 °С and corresponds to exothermic peak at 260-270 °С. The thermogravimetric curve form of a naphthalimide salt depends on the length of hydrocarbon radical of a tetraalkylammonium cation. Thermal analysis data for tetrabutyl- and tetrahexylammonium salts conform to predicted mechanism of Hoffmann elimination that lead to corresponding naphthalimide, tertiary amine and alkene as reaction products. Significant deviations are only detected in the case of tetraoctylammonium salts, that can be explained with formation of high boiling trioctylamine during elimination.