Alumina Perchloric Acid (Al₂O₃-HClO₄) as an Efficient Heterogeneous Catalyst for Modified Preparation of Trimethylsilyl Ethers

Abstract

A highly efficient and mild procedure for the trimethylsilylation of a wide variety of alcohols, including primary, benzylic, secondary, hindered secondary, tertiary, phenols, and oximes with hexamethyldisilazane (HMDS) using alumina perchloric acid (Al 2 O 3 -HClO 4 ) as recyclable heterogeneous catalyst in excellent yields with short reaction times (3−65 min) under ambient conditions is described.

Preparation and characterization of a RHA/TiO2nanocomposite: introduction of an efficient and reusable catalyst for chemoselective trimethylsilyl protection and deprotection of alcohols and phenols

“…Silylation of various benzylic alcohols containing electron-withdrawing and electron-donating substituents in the ortho, meta, and para positions of the benzene ring proceeded efficiently with high isolated yields (Table 4, entries 1-11). Primary, secondary and tertiary aliphatic alcohols were also efficiently converted to their corresponding silyl ethers in almost quantitative yields at room temperature (Table 4, entries [12][13][14][15]. The trimethylsilylation of phenol and its derivatives was also investigated using this method and the desired products were obtained in excellent yields (Table 4, entries [16][17][18][19][20].…”

“…For the activation of this reagent a variety of catalysts have been reported. [3][4][5][6][7][8][9][10][11][12][13][14] Although these procedures provide an improvement in the synthesis of trimethylsilyl ethers, many of them suffer from disadvantages such as long reaction times, harsh reaction conditions, need to excess amounts of the reagent, thermal instability, by-products formation, use of toxic reagents and non-recoverability of the catalyst. Additionally, only some of them are useful for the protection as well as deprotection of the mentioned silyl ethers.…”

Perchloric Acid and Its Salts: Very Powerful Catalysts in Organic Chemistry

“…The trimethylsilylation of hydroxyl groups is also easily carried out at room temperature in the presence of supported perchloric acid on both silica 215 and alumina. 216 Alcohol/ HMDS/HClO 4 -SiO 2 (1:0.8:0.05) in acetonitrile are the best conditions, and silylated products are obtained in excellent isolated yields (85-98%) in very short times. Trimethylsilylation of aldoxime and ketoxime also produces the corresponding trimethylsilylated compounds at these conditions.…”