Comparative Study on Methods for the Determination of Acidity of Industrial Ethyl Cyanacetate

A comparative study on the results obtained by 3 alternative alkalimetric titration of acidity of ethyl cyanacetate was made and discussed.The 3 alternations are: ① visual detection of end point with indicators;② detection of end-point by potential change,that is,the titration performed by an automatic potentiometric titrator;and ③ acid in the sample was separated by extraction with water or saturated sodium chloride solution and the acidity determined by alkalimetric titration in the aqueous solution.As shown by the experimetal results,for the first alternation,among 10 different indicators tested,methyl red was found to be the best one,giving sharp color change at the end point,but as a whole,results obtained by this method were erroneous.For the second alternation,a clear and sharp inflection was observed potentiometrically at the end-point,and accurate and precise results were obtained by this method.In addition,the automatic potentiometric titration was also rapid and convenient in operation.For the third alternation,by using sat′d NaCl solution as extractant,the results obtained were in consistency with the potentiometric method,but the whole analytical procedure was quite time-consuming and tedious.