octadecadienoic-acid and dimethyl-disulfide

The dimethyl disulfide (DMDS) adduct method is one of the more effective methods for determining double bond positions of dienoic acid. The DMDS method can be simply used to obtain the characteristic ions in which cleavage occurs between the methylthio group-added double-bond carbons as can be seen in the mass spectrum obtained using gas chromatography/electron ionization-mass spectrometry. In the case of the methylene-interrupted di-cis type and di-trans type dienoic acid, the DMDS addition reaction only occurs at one double-bond position, and cannot occur at the remaining double-bond position due to steric hindrance. As a result, two types of adducts are produced in the addition reaction. However, in the case of the methylene-interrupted mono-trans (mono-cis) type dienoic acid, the DMDS addition reaction only occurs at the cis-double bond. As a result, one type of adduct is produced in the addition reaction. In this report, we investigate the cause of the reaction selectivity by focusing on the addition reaction time.

Topics: Disulfides; Esters; Fatty Acids, Unsaturated

The dimethyl disulfide derivatization of ethyl (9Z,12Z)-9,12-octadecadienoate and ethyl (9E,12E)-9,12-octadecadienoate was studied. These methylene-interrupted dienes were reacted with dimethyl disulfide and I2 for 72 h at 50 degrees C and the tetrahydrothiopyran, thietane, and tetrahydrothiophene derivatives thus obtained were analyzed by gas chromatography-mass spectrometry. Each configurational isomer displayed a unique gas chromatography trace for the 4-, 5- and 6-membered ring cyclization products thus obtained. Therefore, the cis-cis and trans-trans double bond stereochemistry of 9,12-octadecadienoates can now be determined by dimethyl disulfide derivatization.

Topics: Chromatography, Gas; Disulfides; Esters; Fatty Acids, Unsaturated; Mass Spectrometry; Molecular Conformation; Molecular Structure