Epoxides are cyclic ethers with a three-atom ring. This ring is strained and hence usually highly reactive. Whereas the reaction of amines with terminal epoxides is fast, well known, and used in various applications, the reaction with internal epoxides, such as those of epoxidized fatty acids, does not proceed readily. This hinders the usage of epoxidized vegetable oils as starting material for chemical applications.
Zoran Petrovic, Pittsburg State University, Kansas, USA, and colleagues studied the reactivity of internal epoxides with primary amines by the use of a model internal epoxide compound, 9,10-epoxyoctadecane (E-OCD, pictured), which was reacted with n-octylamine. The reaction took place at temperatures 100 °C, 170 °C, or 200 °C for 24 h without the addition of a catalyst. The resulting products were investigated by gel permeation chromatography (GPC), infrared spectroscopy (IR), and nuclear magnetic resonance spectroscopy (NMR).
The team found that in the absence of a catalyst, ring opening of the internal epoxide with the amine does not take place to any significant extent. Even at 200 °C the conversion rate does not exceed 10 %, regardless of the amine to epoxy ratio.
OH groups could act as reactants and/or catalysts and ring opening hattens to a higher extend in their presence. These results can help to understand the reaction of epoxidized vegetable oils with amines, where amidation resulting in the formation of OH groups, is the key step.
- Study on the Reaction of Amines with Internal Epoxides,
Dragana Radojčić, Jian Hong, Mihail Ionescu, Xianmei Wan, Ivan Javni, Zoran S. Petrović,
Eur. J. Lipid Sci. Technol. 2016.