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

Rapid communications in mass spectrometry : RCM (2012-05-05)
Corinne Loutelier-Bourhis, Ornella Zovi, Laurence Lecamp, Claude Bunel, Marie Hubert-Roux, Catherine M Lange
ABSTRACT

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. 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. 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. 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'.

MATERIALS
Product Number
Brand
Product Description

Sigma-Aldrich
Methyl linoleate, ≥98% (GC)
Supelco
Methyl linoleate, analytical standard
Sigma-Aldrich
Ethyl oleate, 98%
Sigma-Aldrich
Ethyl oleate, tested according to Ph. Eur.
Sigma-Aldrich
Ethyl oleate, natural, ≥85%
Supelco
trans-9,12-Octadecadienoic acid methyl ester, certified reference material, 10 mg/mL in heptane
Sigma-Aldrich
Methyl linolelaidate, ≥99% (GC), liquid
Supelco
Methyl linolelaidate, analytical standard
Supelco
cis-9,cis-12-Octadecadienoic acid methyl ester, certified reference material, 10 mg/mL in heptane
Sigma-Aldrich
Ethyl oleate, technical grade, 70%