The acylation of 2-methoxynaphthalene with acetic anhydride over Nafion/silica composites and BEA zeolites containing Lewis acid sites

The influence of Nafion content (5–80 wt%) in different Nafion/silica composite materials (SAC) as well as the effect of different solvents was studied in liquid phase Friedel-Crafts acylation of 2-methoxynaphthalene (2-MN) with acetic anhydride. The higher the Nafion content, the higher are conversion and selectivity (up to 69%) to the desired product 2-acetyl-6-methoxynaphthalene (2,6-ACMN). Unpolar solvents such as toluene or methylene chloride favour the formation of 1-acetyl-2-methoxynaphthalene (1,2-ACMN) while polar solvents like nitrobenzene or sulfolane promote the 2,6-ACMN formation. Further investigations are related to the influence of metal ions, e.g. Al3+, Fe3+, Zn2+, Cu2+ and Ag+ in ion-exchanged Nafion–silica composite on the formation of the desired 2,6-ACMN. An increase in selectivity to 2,6-ACMN in comparison with the pure acidic Nafion–silica was observed.Zeolites containing Lewis acid sites created by ion-exchange with Fe3+, Cu2+ and Ag+ were investigated in the heterogeneously catalysed acylation of methoxynaphthalene for comparison reasons.

Graphical abstractThe authors have investigated the use of Nafion/silica composite materials with Nafion contents ranging from 5 to 80 wt% and the influence of different solvents in the acylation of 2-methoxynaphthalene. It was found that the yield of desired product (2-acetly-6-methoxynaphthalene) increased both with increasing Nafion content of the catalyst and solvent polarity. Further experiments were performed with metal ion-exchanged Nafion/silica composite materials and – for comparison reasons – zeolite H-BEA and metal doped H-BEA. Figure optionsDownload full-size imageDownload as PowerPoint slide