p-Sulfonic acid calix(n)arenes as organocatalysts for the transesterification reaction of Passiflora seed oil

The catalytic activity of p-sulfonic acid calix(4)arene was studied in the transesterification reactions of Passiflora seed oil with methanol or ethanol. Calix(n)arenes are highly versatile organocatalysts and conversion rates(98 % were obtained for the transforma- tion of Passiflora seed oil to its methyl or ethyl esters after 5 h of reaction in the presence of p-sulfonic acid calix(4)- arene (3.52 mol % in ethanol; 5.28 mol % in methanol). Moreover, the organocatalyst was recovered and reused in two subsequent cycles without a significant decrease in the activity or selectivity. The use of a non-corrosive and reu- sable organocatalyst is the positive aspect of this process. Graphical abstract