Cyanohydrin formation of quinone appended benzaldehyde as a tool for selective colorimetric detection of cyanide in aqueous solution in a wide pH range

A Novel chemosensor R possessing napthoquinone substituted benzaldehyde has been successfully designed, synthesized and characterized using NMR and mass spectral techniques. The receptor exhibits striking colour change from pale yellow to intense green with sodium cyanide in DMF-H2O (80–20% v/v) in a wide range of pH (3−12). Based on the results of spectral (UV–Vis, fluorescence and NMR), electrochemical and kinetic studies a plausible mechanism has been proposed for the cyanide detection process. The mechanism of sensing of cyanide by R is through the formation of cyanohydrin in acidic, neutral and basic solutions, which is the novelty of the receptor. The pseudo-first-order rate constants for the formation of cyanohydrin are found to be 2.9 × 10−3, 3.9 × 10−3 and 4.6 × 10−3 min−1 at pH values 5, 7 and 10, respectively in DMF-H2O (80–20% v/v) medium, supporting the ability of R to form cyanohydrin with equal ease in different pH values. The results of Job's continuous variation method indicates a 1:2 (R:CN−) stoichiometry for the interaction. The only minor drawback with the receptor is the time taken to impart visible colour change with cyanide ion, which is not instantaneous.