Design of Metal-free Porphyrin Photocatalyst: Synergetic Effect of Donor–Acceptor Phenomenon for 1, 1-Diethoxyethane Production under Visible Light

Ethanol is known as a significant platform of chemical, obtained by fermentation of renewable sources comprising carbohydrates and lignocellulose. It is a corrosive and ineffective fuel compared to petrol; hence, ethanol needs to convert into other fuel additives for satisfying upcoming demands in chemicals and renewable fuels. Moreover, the chemical transformation of ethanol to fuel additives is still a major task under mild conditions. In this protocol, 1,1-diethoxyethane (DEE) is easily produced from ethanol over metal-free Brønsted acid-functionalized porphyrin (BAFPc) photocatalyst under irradiation of 5 W LED at ambient conditions. Acetalization follows the formation of acetaldehyde by photogenerated holes, evidenced by GC–MS. More prominently, the protocol is efficient and economic with 92% yield DEE from ethanol. The applicability of DEE as additives was explored by blending petrol with 20 and 30% volume. Moreover, engine emission characteristics have been achieved and found that unburnt hydrocarbons, CO, have been drastically reduced compared to commercial petrol. To know the importance of meso-substituents in porphyrin core, various precursors such as formaldehyde, benzaldehyde, benzimidazole-based ionic liquid, benzimidazole-based sulfonic ionic liquid and with electron donor–acceptor group were used for the synthesis of photocatalysts. The results revealed that photocatalyst with donor–acceptor functionality was found effective for the production of DEE that delayed the recombination of electrons and holes. The plausible mechanism indicated that DEE was formed via intermediates including acetaldehyde, ethoxy radical, tetrahedral intermediate, hemiacetal and carbocation, supported by GC–MS analysis. BAFPc was found stable during photocatalytic acetalization and recycled five times with a good yield of DEE. Graphical abstract