FRAGMENTATION OF CONJUGATE BASES OF ESTERS DERIVED FROM MULTIFUNCTIONAL ALCOHOLS INCLUDING TRIACYLGLYCEROLS

Enolate anions of esters from 1,2 and 1,3 diols undergo an internal nu cleophilic substitution reaction that produces a beta-ketoester and an alkoxide ion within the molecular species. These intermediate ions un dergo two competitive fragmentation pathways. The first pathway corres ponds to a second nucleophilic substitution of the ketoester by the al koxide that yields a neutral cyclic ether and the beta-ketoacid carbox ylate. The latter then loses carbon dioxide and produces the enolate a nion of the corresponding ketone. The second proposed pathway is stepw ise: it starts with a proton transfer from the methylene group between the two carbonyls to the alkoxide anion that produces an alcohol and the enolate ion of the beta-ketoester inside the molecular species. Th e latter undergoes cleavage of the ester bond induced by the negative charge to yield an ion-dipole complex composed of a neutral acylketene and an alkoxide ion. The direct dissociation of this ion-dipole compl ex competes with an internal proton exchange to yield a new complex th at consists of an alcohol molecule and the anion of the acylketene, wh ich can also dissociate. The fragmentation pathway that leads to the k etone enolate is sensitive to the relative positions (1,2 or 1,3) of t he esters on the molecular backbone. This position-sensitive reaction is useful for the assignment of the primary and secondary positions in triacylglycerols, even in mixtures, as shown by some examples.