Mechanistic study of maleic anhydride grafting onto fatty double bonds using mass spectrometry.

RATIONALE: The grafting of maleic anhydride onto fatty C=C double bonds is a well-known and used method to functionalize triglyceride molecules. Nevertheless, grafted products are not actually structurally well defined. In this work, the thermal grafting of maleic anhydride onto (un)saturated fatty acid esters without the use of an initiator was characterized in order to determine the nature of the products formed during this reaction. METHODS: Complementary spectrometric techniques, ESI-MS(n) (ion-trap mass spectrometer), IMS-MS(n) (Q-IMS-TOFMS) and GC/MS, were used to identify the grafted products which were prepared using either ethyl oleate (EtO) or methyl linoleate (MeL) as model molecules and maleic anhydride (MA). Lithiated adducts were investigated since they yield useful structural information when subjected to collision-induced dissociation (CID) in tandem mass spectrometry. RESULTS: A high number of products are formed during MA grafting and various reaction types could occur. Radical addition of maleic anhydride followed by combination or elimination reactions led to succinic and maleic anhydride grafting, respectively. The addition occurred with or without double-bond shift; the resulting derivatives showed succinic and maleic anhydride branching in the α-position relative to the double bond or onto the carbon atom of the initial double bond. Some structures obtained by radical addition and combination were also consistent with the Alder ene functionalization reaction. The Diels-Alder addition between di-unsaturated fatty acid chains and maleic anhydride could yield cyclic forms of MA-grafted derivatives. CONCLUSIONS: We have shown that ESI-MS(n) and IMS-MS(n) allow the identification of grafted products providing relevant structural information concerning isomers. These methods permit the rapid and direct analyses of 'crude reaction mixtures'.

Contribution of two approaches using electrospray ionization with multi-stage mass spectrometry for the characterization of linseed oil.

A detailed characterization of triacylglycerols (TAGs) present in linseed oil samples from a local producer was performed using electrospray ionization and two mass spectrometric approaches; direct infusion multi-stage mass spectrometry (MS(n)) experiments and liquid chromatography/tandem mass spectrometry (LC/MS/MS) using non-aqueous reversed-phase chromatographic conditions. The combination of both approaches permitted the identification of 26 TAGs. Comparison of the two analytical approaches showed that discrimination of regioisomers was achieved from MS3 data while other isobaric species were separated and identified by LC/MS/MS analysis. The results we obtained were also compared with those previously reported. The TAG composition of the studied linseed oil is qualitatively identical to that of linseed oils from various sources in Europe, Canada, Argentina or India. However, a few differences were observed with regard to the proportions of some TAGs; these can be explained by variations in the culture conditions, climate, and variety of the seeds.