Abstract
Sodium, lithium, and calcium soaps obtained by saponification of high-oleic sunflower oil were studied by Fourier-transform infrared spectroscopy. Spectra of crude mixtures containing soap, glycerin, residual alkali, and triacylglycerols were compared to those of pure soaps obtained from fatty acids. The infrared spectra of crude soaps showed the same characteristic bands as pure ones. The absorption bands of asymmetric (ω2) and symmetric (ω1) stretching vibrations of the carboxylate group indicated that the metal-oxygen bonds of these soaps had an ionic character whose strength differed from one cationic counterion to another. Once the characteristic absorption bands of the soaps were assigned, a kinetics study of saponification was performed. Saponification by sodium, anhydrous lithium, and calcium hydroxides was an autocatalytic reaction, characterized by an S-shaped kinetics curve, whereas saponification by aqueous lithium hydroxide was stoichiometric. The structure of the metal-oxygen bond played a role in the kinetic mechanisms.
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Abbreviations
- ω1 :
-
carboxylate ion symmetric stretching vibration
- ω2 :
-
carboxylate ion asymmetric stretching vibration
- ω3 :
-
carboxylate bending vibration
- FTIR:
-
Fourier-transform infrared
- HOSO:
-
high-oleic sunflower oil
- TAG:
-
triacylglycerol
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Poulenat, G., Sentenac, S. & Mouloungui, Z. Fourier-transform infrared spectra of fatty acid salts—Kinetics of high-oleic sunflower oil saponification. J Surfact Deterg 6, 305–310 (2003). https://doi.org/10.1007/s11743-003-0274-1
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DOI: https://doi.org/10.1007/s11743-003-0274-1