Resumen de Obtaining the Iodine Value of Various Oils via Bromination with Pyridinium Tribromide
Michael Simurdiak, Olushola Olukoga, Kirk Hedberg
A laboratory exercise was devised that allows students to rapidly and fairly accurately determine the iodine value of oleic acid. This method utilizes the addition of elemental bromine to the unsaturated bonds in oleic acid, due to bromine’s relatively fast reaction rate compared to that of the traditional Wijs solution method. This method also uses pyridinium tribromide as a bromine source in an effort to eliminate many of the safety hazards of working with elemental bromine. After the addition of a known quantity of bromine to the reaction flask, excess bromine is reduced with potassium iodide forming elemental iodine. The elemental iodine is then titrated with sodium thiosulfate and a starch indicator in a back-titration to determine the amount of excess bromine added to the oleic acid. Students then determine the iodine value of oleic acid by using a 126 g iodine/80 g of bromine ratio. This exercise can yield results fairly close to the accepted iodine value of 90 for oleic acid, as several of the groups who tried out the experiment obtained iodine values close to 90. In addition, this exercise was also able to determine the iodine values of olive, coconut, and grapeseed oils. Finally, this experiment can be used to reinforce organic chemistry concepts as well as biochemistry concepts to IB Chemistry students.
