Fatty acids of Thespesia populnea: Mass spectrometry of picolinyl esters of cyclopropene fatty acids

Abstract

Thespesia populnea belongs to the plant family of Malvaceae which contain cyclopropane and cyclopropene fatty acids. However, previous literature reports vary regarding the content of these compounds in Thespesia populnea seed oil. In this work, the content of malvalic acid (8,9-methylene-9-heptadecenoic acid) in the fatty acid profile of Thespesia populnea seed oil was approximately 7% by GC. Two cyclopropane fatty acids were identified, including dihydrosterculic acid. The methyl and picolinyl esters of Thespesia populnea seed oil were also prepared. The mass spectrum of picolinyl malvalate was more closely investigated, especially an ion at m/e 279, which does not fit the typical series of ions observed in picolinyl esters. It is shown that this ion is caused by cleavage at the picolinyl moiety and contains the fatty acid chain without the picolinyl moiety. This type of cleavage has previously not been observed prominently in picolinyl esters and may therefore be diagnostic for picolinyl esters of cyclopropene fatty acids. The NMR spectra of Thespesia populnea methyl esters are also discussed. Practical applications:The work reports the fatty acid composition of Thespesia seed oil whose derivatives have not yet been extensively utilized for industrial purposes, for example, biodiesel. Knowing this composition is essential for understanding potential uses and, for example, in case of biodiesel the fuel properties. Besides this issue, some data (mass spectrometry and NMR) crucial for obtaining the composition information are analyzed in detail. The biodiesel properties of methyl esters of Thespesia populnea will be reported separately.

Identification of the Unsaturated Heptadecyl Fatty Acids in the Seed Oils of Thespesia populnea and Gossypium hirsutum

“…A few reports have appeared that discuss the composition of T. populnea seed oil. Subbaram [6] reported an iodine value for T. populnea seed oil that seems low (71.5) given his and other reported fatty acid profiles for the oil [6][7][8]. The value obtained in this work (98.8) is in better agreement with the reported fatty acid data.…”

“…Among these were seeds of Thespesia populnea. Chromatography of the methyl esters from this plant's seed oil suggested that the oil contained 10-to 20-fold higher levels of these oddchain fatty acids, which have not been mentioned in prior analyses of the plant's oil [6][7][8].…”

“…Subbaram's higher level of 9-18:1 appears to be due to the inclusion of the cyclopropenoid acids with this component. More recently, Knothe et al [8] have reported a composition that is similar regarding the common components, but also identifies a 9,10-methylene-hexadecyl fatty acid (9,10-CPA17:0) and CPA19:0 but does not report CPE19:1. This profile diverges somewhat from what is generally reported for Malvaceae plants [26], where CPE18:1 and CPE19:1 are usually observed and CPA19:0 is often noted.…”

Fatty Acid Profile of Kenaf Seed Oil

“…Sterculic acid was identified by the shift of the characteristic peaks to m/z 286 and 293 but was present only in very minor amounts. The mass spectral cleavage pattern, which corresponds to that of picolinyl malvalate [33], albeit with a shift of 14 amu for peaks generated by cleavage between the picolinyl and cyclopropenyl moieties, agrees with other results [34]. On the other hand, dihydrosterculic acid was present in amounts similar to malvalic acid while dihydromalvalic acid was not observed, which could be due to peak overlapping or minute amounts thereof.…”

“…Besides this observation, several cyclic fatty acids not previously discussed or quantified in kenaf seed oil were detected. The presence of malvalic acid was unambiguously shown by the mass spectrum of its picolinyl ester which displays a typical pair or peaks at m/z 272 and 279 in the corresponding mass spectral pattern discussed previously [33]. The presence of malvalic acid, which has an unusual odd-numbered (C17) fatty acid chain can be seen in conjunction with the presence of 8-heptadecenoic acid, as heptadecenoic acid is likely the biogenic precursor of malvalic acid [21].…”