Synthesis of Fluorescent Indicator: Salicylaldehyde Salicylhydrazone

In places such as the Yellow River, high metal concentrations in the water can negatively affect organisms in the biome. High metal concentrations and substandard water conditions can be detected using salicylaldehyde salicylhydrazone, a synthetic fluorescent probe. Salicylaldehyde salicylhydrazone was synthesized in three steps using salicylic acid and methanol. In the first step of the reaction, heat was used for esterification of salicylic acid and methanol, and the reaction was purified using extraction. The methyl salicylate produced from the first step was refluxed with hydrazine hydrate and absolute ethanol to form hydrazide salicylate. During the final step, salicylaldehyde was added to the previous intermediate and refluxed until precipitate was present. This yielded the final product of salicylaldehyde salicylhydrazone. Due to environmental concerns, methanol was substituted for ethanol in the first step of the synthesis. This created less waste through atom economy calculations, used less energy to heat the reaction, and has less hazardous effects to humans.