Brønsted acid-functionalized Cu(ii) porphyrin entangled with a benzimidazolium-based ionic liquid for the photocatalytic acetylation of 1°, 2° and 3° alcohols with aromatic/aliphatic acids

Abstract

Benzyl ethanoate is a vital industrial ester with various applications in flavouring agents, air fresheners, and other consumer products like soap and detergents due to its attractive aroma and efficient solvent characteristics. In this work, a Brønsted acid-functionalized Cu(II)–porphyrin (BACuPc) entangled with a benzimidazolium ionic liquid was synthesized and characterized by ¹H NMR, solid-state ¹³C NMR, and FT-IR spectroscopies and p-XRD. The surface area and proton strength (H₀ = 1.157) were determined by BET technique and Hammett acidity analysis, respectively. Its energy band gap (1.39 eV) was determined from the diffuse reflectance spectrum. The photocatalytic performance of BACuPc was scrutinized for the esterification of 1°, 2°, and 3° alcohols with aromatic/aliphatic acids, including a scaled-up (250 mL) synthesis of two esters, and 37 derivatives were achieved. Applying optimized photocatalytic conditions, such as 2.0 wt% (0.013 mmol) BACuPc photocatalyst loading, 1 : 1.2 ROH : RCOOH molar ratio, and irradiation with a 5 W LED light, afforded 89% benzyl ethanoate in 20 h. The yield of benzyl ethanoate decreased with increasing C-chain length and branching of the alcohols. The plausible pathway of photo-esterification was followed via Langmuir–Hinshelwood mechanism and was supported by the formation of alkoxy radical using trimethyl phosphite [m/z = 226.47] by GC-MS. Further, the physicochemical properties of gasoline and diesel blended with 15% t-butyl ethanoate and n-hexyl ethanoate, respectively, were found to be comparable with those of marketed gasoline and diesel samples. Similarly, engine performance and emission characteristics of diesel blended with 15% n-hexyl ethanoate were found to be remarkable compared with those of commercial diesel samples. BACuPc exhibited good photocatalytic recyclability and stability, as confirmed by ICP-MS and atomic absorption spectroscopy.