Determination of the enol form of β-diketones in alcohol

Abstract

A method for the determination of the enol form of various β-diketones in ethanol was established by modifying Meyer's method. An ethanol solution of bromine of about 4 times for the sample concentration was added to the sample solution which was kept at a constant temperature. After standing for an optional time, 0.1 M β-naphthol in ethanol was added until complete decoloration of the solution. The solution was brought to a room temperature, and 10 ml of 10% aqueous solution of potassium iodide was added. The apparent enol content including the enol form produced by the shift of the keto-enol equilibrium was determined by the titration of the liberated iodine with 0.1 N sodium thiosulfate. To subtract the enol form produced by the shift of the equilibrium, the apparent enol content measured was plotted against the standing time. The enol form originally present in ethanol was then estimated by extraporating the linear portion of the resulting curve to the standing time "zero".