Synthesis and characterization of estolide esters containing epoxy and cyclic carbonate groups

Authors: Doll, Kenneth - Ken; Cermak, Steven - Steve; Kenar, James - Jim; Isbell, Terry

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2016
Publication Date: 7/25/2016
Publication URL: http://handle.nal.usda.gov/10113/5642480
Citation: Doll, K.M., Cermak, S.C., Kenar, J.A., Isbell, T.A., 2016. Synthesis and characterization of estolide esters containing epoxy and cyclic carbonate groups. Journal of the American Oil Chemists' Society. 93(8):1149-1155.

Interpretive Summary: ARS has been working on the development of vegetable oil based lubricants for many years. One of the more successful projects has been in the creation of a compound called an estolide. This material is now being used by a commercial partner for a variety of applications. However, there are some limitations on just what the estolide can be used for, limitations which may be overcome and a wider variety of products made possible. Chemical reactions which add a group called a cyclic carbonate to ordinary vegetable oils have been performed at ARS in the past. The extension of this technology to estolides has been accomplished, and the new “carbonated estolide” made and characterized. It has higher viscosity than ordinary estolide, which may be desirable in many industrial applications. This is just one more way that we are increasing the versatility of proven technologies and improving the industrial uses for U.S. agriculture.

Technical Abstract: The unsaturated sites in oleic 2-ethylhexyl estolide esters (containing 35% monoenic fatty acids) were converted into epoxide and five-membered cyclic carbonate groups and the products characterized by Fourier transform infrared spectra (FTIR), 1H-, and 13C-nuclear magnetic resonance (NMR) spectroscopies. Epoxidation of the alkene bonds was accomplished using performic acid generated in situ from formic acid and hydrogen peroxide. Greater than 90% alkenes were converted into their corresponding epoxide groups as determined by oxirane values and the epoxide ring structure was confirmed by 1H- and 13C-NMR. The estolide ester epoxide material was subsequently reacted with supercritical carbon dioxide in the presence of tetrabutylammonium bromide catalyst to produce the corresponding estolide ester containing the cyclic carbonate group. The signals at 1,807 cm-1 and delta 82 ppm in the FTIR and 13C-NMR spectra, respectively, confirmed the desired cyclic carbonate was produced. The carbonated estolide ester exhibited a dynamic viscosity, at 25 deg. C, of 172 mPa’s as compared to 155 mPa’s for the estolide ester starting material. The estolide ester structure of these new derivatives was shown to be consistent throughout their synthesis.