Catalysis of Thermal Isomerization of Methyl Yellow by Salts.

Cu2+ ions are reported to catalyze the thermal isomerization (TI) of cis-azobenzene. It was found that some alkali halides (NaCl, KCl, NaBr, and KBr) also catalyze the TI of 4-dimethylamino-azobenzene in ethanol. These tendencies were attributed to the interaction between the azo group and the cation based on experimental data and density functional theory (DFT) calculations. Some Na salts (CH3COONa, Na2HPO4, and Na2SO3) were found to inhibit the TI of 4-dimethylamino-azobenzene in ethanol. It is inferred that the weak acid ions in these salts decrease the concentration of H+ ions that catalyze the TI process.