Obtaining the Iodine Value of Various Oils via Bromination with Pyridinium Tribromide

Abstract

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.

Durable Cellulose–Sulfur Composites Derived from Agricultural and Petrochemical Waste

“…Qualitative evidence that substitution had taken place was provided by Fourier‐transform infrared spectroscopy, which showed a CH bending band at 900 cm −1 attributable to a geminally substituted olefin (Figure S1, Supporting Information). The degree of substitution (i.e., the percentage of cellulose repeat units that had been alkylated) in PC was calculated to be 12 ± 1% from iodometric titration, in which a color change is monitored as alkenes react with in situ generated Br 2 , a standard method for quantifying unsaturation in carbohydrate research . Whereas the substitution of the primary alcohol is shown in Scheme , there could be a smaller fraction of substitution at secondary alcohols.…”

“…[13] Qualitative evidence that substitution had taken place was provided by Fourier-transform infrared spectroscopy, which showed a CH bending band at 900 cm −1 attributable to a geminally substituted olefin ( Figure S1, Supporting Information). [13,14] Whereas the substitution of the primary alcohol is shown in Scheme 2, there could be a smaller fraction of substitution at secondary alcohols. [13,14] Whereas the substitution of the primary alcohol is shown in Scheme 2, there could be a smaller fraction of substitution at secondary alcohols.…”

“…The degree of substitution (i.e., the percentage of cellulose repeat units that had been alkylated) in PC was calculated to be 12 ± 1% from iodometric titration, in which a color change is monitored as alkenes react with in situ generated Br 2 , a standard method for quantifying unsaturation in carbohydrate research. [13,14] Whereas the substitution of the primary alcohol is shown in Scheme 2, there could be a smaller fraction of substitution at secondary alcohols. Regarding the polymer morphology, X-ray diffraction data ( Figure S5, Supporting Information) confirm that PC is an amorphous polymer that does not feature fibrous or crystalline structures, so PC is appropriate for homogeneous blending with the sulfur comonomer in the subsequent step.…”

Minimally Invasive Hemostatic Materials: Tackling a Dilemma of Fluidity and Adhesion by Photopolymerization in situ

“…The concentration of sodium hydroxide was adjusted to 30%–50% before use. The degree of unsaturation of SAE was obtained by iodometry (Wijs method) 26 . HMPP and TPO-L were purchased from Ciba Specialty Chemicals Co., Ltd. and purified by distillation.…”

Calibrated Optical Markers to Study Thermal Degradation in Edible Oils Using Raman and Optical Transmission Spectroscopy

“…22–24 To promote it as an alternative and facile methodology to study thermally stressed edible oils, it has to be correlated vis-à-vis a quantifiable parameter and then calibrated. This can be done through “iodine value”, 25,26 or “bromine value”, 27 which is defined as the mass of iodine/bromine, in grams, to react with 100 g of a chemical and is a measure of the degree of unsaturation in FAs present in edible oils.…”