Visible light assisted sulfonic acid-functionalized porphyrin comprising benzimidazolium moiety for photocatalytic transesterification of castor oil

A novel sulfonic acid-functionalized porphyrin comprising benzimidazolium moiety (SAFPBM) was prepared using 1-(3-formyl-2-hydroxybenzyl)-3-(4-sulfobutyl) (3a), dihydro-1H-benzo[d] imidazole-3-ium(oxidosulfinyl) bis(I1-oxy) (7a) and pyrrole in stoichiometric proportions. The synthesized photocatalyst was confirmed by various characterizations and assessed as a potential photocatalyst for the conversion of castor oil to biodiesel component by reaction with alcohols in presence of visible light irradiations (5 W/9W/12 W LED). The photocatalyst with 0.70 Hammett acidity, achieved 94% methyl ricinoleate in 18 h using 15 mg under visible light at ambient temperature and 6:1 methanol: castor oil ratio. SAFPBM displayed admirable photocatalytic activity with recyclability for 7 runs, towards the transesterification of castor oil and other vegetable oils at room temperature. The formation of methyl recinoleate was confirmed by NMR, DEPT, HRMS, HPLC and successfully hydrogenated to methyl 12-hydroxyoctadecanoate using HCOOH as a hydrogen source. A plausible reaction mechanism for the formation of methyl ricinoleate is projected via formation of H+, CH3O* and unstable tetrahedral intermediate on Photocatalytic surface.

Automated summary

A novel sulfonic acid-functionalized porphyrin containing benzimidazolium moiety (SAFPBM) displayed remarkable photocatalytic activity under visible light irradiation, facilitating the conversion of castor oil to biodiesel component with good recyclability. The formation mechanism of methyl ricinoleate and its hydrogenation product were confirmed through various analytical techniques.