Acid-Promoted Reactions of Ethyl Linoleate with Nitrite Ions: Formation and Structural Characterization of Isomeric Nitroalkene, Nitrohydroxy, and Novel 3-Nitro-1,5-hexadiene and 1,5-Dinitro-1,3-pentadiene Products

The reaction of ethyl linoleate (1) with NO(2)(-) in different air-equilibrated acidic media resulted in the formation of complex patterns of products, some of which could be isolated by repeated TLC fractionation and were formulated as the nitroalkenes 2-5, the novel (1E, 5Z)-3-nitro-1,5-hexadienes 6/7, the novel (E,E)-1, 5-dinitro-1,3-pentadiene derivatives 8 and 9, and the nitro alcohols 10/11 and 12/13 by extensive GC-MS and 2D NMR analysis, as aided by 1D Hartmann-Hahn proton mapping experiments. Similar reaction of methyl oleate gave mainly nitroalkene (14/15) and allylic nitro derivatives (16/17). Formation of 2-13 may be envisaged in terms of HNO(2)-mediated nitration pathways in which regioisomeric beta-nitroalkyl radical intermediates derived from attack of NO(2) to the 1,4-pentadiene moiety of 1 evolve through competitive H-atom abstraction and free radical combination routes.