Determination of critical micelle concentrations of some nonionic surfactants by Keto‐Enol tautomerism of benzoylacetoanilide

Abstract

Abstract The absorbances of benzoylacetoanilide, keto‐enol tautomer, dissolved in aqueous solution of several concentration ranges below and above the CMC of the incorporating surfactants. Below the CMC, the absorbance of the band at 250 nm due to the ketonic form showed hardly any change and that of the band at 320 nm due to the enolic form could not be observed. In contrast, above the CMC, the spectral band of the enolic form appeared, and the absorbance increased abruptly and that due to the ketonic form decreased gradually. The changes at the CMC in absorbance for these nonionic surfactants were distinctly observed by plotting the absorbance at 250 and 320 nm as a function of the concentration of surfactants. These changes at the CMC were very noticeable with nonionic surfactants as well as with ionic surfactants. The concentrations corresponding to break points for these surfactants were in fairly good agreement with the published data of the CMC of each surfactant. This method of keto‐enol tautomerism using benzoylacetoanilide has been confirmed CMC for most anionic, cationic, and nonionic surfactants.