Decarbonylation of two α-diketones: 1,2-Bis(6-methylpyridin-2-yl)ethane-1,2-dione and 1-(pyridin-2-yl)-2-(6-methylpyridin-2-yl)ethane-1,2-dione

EI mass fragmentation of the 1,2-bis(6-methylpyridin-2-yl)ethane-1,2-dione and 1-(pyridin-2-yl)-2-(6-methylpyridin-2-yl)ethane-1,2-dione radical cations gave rise to a sequence of unexpected composite ion peaks. The molecular ion m/z 240 gives mass measurements of metastable ions at m/z 212 and 184 and the molecular ion m/z 226 gave peaks at m/z 198 and 170 resulting from the successive loss of two fragments of 28 mass units each, corresponding to CO. These fragmentations yield the products [CH3C5H3NCOC5H3NCH3]+, [(CH3C5H3N)2]+ and [C5H4NCOC5H3NCH3]+, C5H4NC5H3NCH3]+, respectively, as confirmed by mass determination identification of the precursor ions and decomposition product ions. In addition, the prominent ions [CH3C5H3NCO]+, [OCNH3C5CH3]+, [C5H3NCO]+ and [OCNH3C5CH3]+, arising from cleavage of the CC bond, were detected in similar abundance ratios for both fragments and the corresponding secondary fragments, which can be attributed to the dissociation of several ionized α-diketones. The ionized homologue α-diketone 1,2-dipyridyldione also exhibited a decarbonylation channel yielding the molecular ion m/z 212, and before losing CO gave peaks at m/z 184 and 156. The fragmentation of 1,2-diphenylethane-1,2-dione did not exhibit the same behavior. The results confirm that the green co-crystal obtained is a co-compound formed of 1,2-bis(6-methylpyridin-2-yl)ethane-1,2-dione and 1-(pyridin-2-yl)-2-(6-methylpyridin-2-yl)ethane-1,2-dione.