A Colorimetric Method for the Determination of Esters

The colorimetric method of Hill, based on conversion of esters to hydroxamic acids which form red complexes with ferric ion, has been adapted for the estimation of volatile esters. Investigation of the factors influencing the two reactions involved has led to a satisfactory procedure for esters derived from acids with an unbranched chain of two to ten carbon atoms and esters of isobutyric and isovaleric acids. The degree of conversion to ferric hydroxamate complexes has been found by reference to pure hydroxamic acids. The absorption spectra of the ferric hydroxamate complexes from all the esters examined show a maximum absorption at 520 mμ. Hence a mixture of esters may be estimated in terms of one of the esters.