Addition of C1- C8 Alcohols to Fatty Acid Ester C=C Bond under Heterogeneous Catalytic Conditions

Low thermal and oxidation stability limits the use of vegetable oils and derived esters because of the presence of C=C double bonds. The reactivity of this double bond has been investigated to perform the addition of C1-C8 alcohols, in the presence of H-form zeolites, thus leading to saturated oxygen-containing side chains.
On the chemical side, our previous results relative to the model reaction -addition of methanol to methyl oleate- have shown the influence of key parameters acting on the yield of the target product, methyl methoxy stearate (temperature, methanol excess, Si/Al ratio). The present study deals with an even more complex system: in addition to C=C bond migration and to a thermodynamic limitation related to the reverse reaction (de-methoxylation), already noted, methyl oleate here also undergoes alcoholysis as a parallel reaction, thanks to the acidic properties of the solid catalyst. Selectivity and reaction rates are discussed according to steric and electronic effects, the alcohol being solvent but also reactant upon the case. The initial rate of the alcoholysis being about 4 to 10 times faster than the addition to C=C, the reaction medium first contains the ester with the higher alcohol, which is then alkoxylated at almost constant initial rate whatever the chain length from methanol to n-butanol.
On the applied side, this work opens the way to a range of oleochemicals under “green” conditions; the catalyst yields C=C free alkoxylated long chain esters, including a di-alkoxylated chain when starting from linoleate, with selectivity higher than 70 mole%. The adduct is similar to a branched chain wax when starting from a common unsaturated ester, or is a normal chain wax but bearing an oxygen bridge in place of one CH2 when starting from undecylenic ester. All these “new” alcoxylated esters –not yet manufactured at industrial scale but accessible- should bring interesting properties for example in lubricant and cosmetic formulations.