Synthesis and applications of isopropenyl esters

A general solvent-free protocol for the synthesis of isopropenyl esters (iPEs) was developed and applied to different renewable based carboxylic acids and their acyl chlorides derivatives, relying on the use of sulfuric acid as catalyst. Isopropenyl acetate, a potentially renewable, cheap and non-toxic reagent, was used as “isopropenyl synthon source” for the synthesis of isopropenyl esters. Benzoic, p-methoxy benzoic, octanoic, phenylbutirric, levulinic, oxalic, malonic and succinic acids were used. Furthermore, Brønsted acid ionic liquids (BAILs) were tested for the synthesis of iPEs. The protocol could also be extended to dicarboxylic acids, e. g. oxalyl chloride and succinyl chloride, upon simple modifications of the reaction setup (reaction performed in presence of a solvent using a heterogeneous acid catalyst). Some of these synthesized iPEs (isopropenyl benzoate, octanoate and phenylbutyrate) and iPA were let react with 1,2-propanediol and ethylene glycol, under resin Amberlyst-15 catalysis, in order to study their reactivity. The aim was to obtain simultaneously the respective monoesters and acetals, exploiting the production of acetone by-product during the transesterification process. A comparison among the tested isopropenyls towards this tandem-type reaction was obtained.