Alkylation of 2-methoxynaphthalene with propylene oxide using titanium molecular sieves Original Research Article

The alkylation of 2-methoxynaphthalene (2-MN) with propylene oxide (PO) to form an intermediate for the synthesis of naproxen is investigated using molecular sieves that do not contain Bronsted acid sites. Titanium-containing, pure-silica beta (Ti-BEA) is shown for the first time to allow the title reaction to proceed. At low temperatures (ca. below 423 K) Ti-BEA alone does not have sufficient activity to promote the alkylation. However, when Ti-BEA is treated with compounds that can ligate the framework Ti-sites, e.g., perfluoro-tert-butanol or pentafluorophenol, an active solid is achieved. The reaction products are an O-alkylated product (I) and four C-alkylated products; 1-(2-methoxy-1-naphthyl)-2-propanol (II), 2-(2-methoxy-1-naphthyl)propanol (III), 1-(6-methoxy-2-naphthyl)-2-propanol (IV) and 2-(6-methoxy-2-naphthyl)propanol (V). The C-alkylated products show a preference for the 2,6-isomers and catalysis can occur in the presence of poisons too large to enter the porous solid. These results reveal the presence of intracrystalline active sites. The presence of pentafluorophenol causes titanium to be leached from Ti-BEA that is not active for alkylation at lower temperatures. However, at 423 K the leached titanium is active and significantly contributes to the observed product yields. This leaching is increased with longer reaction time and with increasing amount of pentafluorophenol.