Silica Chloride Nano Particle Catalyzed Ring Opening of Epoxides by Aromatic Amines

Epoxides are versatile intermediates in organic synthesis and a large variety of reagents are known for the ring opening of these compounds. β-Amino alcohols are among the most important precursor for a wide range of biologically active natural and synthetic products, unnatural amino acids and chiral auxiliaries. The practical route for synthesis of β-amino alcohols is direct aminolysis of epoxides in presence of surplus amine at elevated temperature. However, this methodology suffers from one or more disadvantages such as high toxicity and corrosiveness of the acids employed, moisture sensitivity of catalyst systems, high temperature, hazardous organic solvent, extended time and the use of catalyst in a stoichiometric amount or inconvenient handling procedures. Therefore, continuous efforts have been made to develop catalyst free and various catalysts such as sulfamic acid, metal triflates, metal alkoxides, metal halides, transition metal salts, heteropolymolybdate or tungstate, for the synthesis of β-amino alcohols. Other limitations such as low yields, failure of deactivated amines and sterically demanding aromatic amines are associated with most of the literature methods. Therefore, the introduction of new and efficient methods is still in demand. The use of heterogeneous catalysts provides a perfect solution to overcome the above limitations. In recent years, the use of reagents and catalysts on solid supports has made significant progress. Nano silica gel is one of the extensively used surface material supports for different chemical transformations in organic chemistry. One of such modified nano silica is nano silica chloride (nano SiO2-Cl), which at the first time we reported to be an efficient catalyst for the synthesis of many organic compounds such as the amorphous silica chloride. Solid Solid acid catalysts such as amberlyst-15, monodispersed silica nanoparticles, zeolites, montmorillonite K10 and ionic liquids, functionalized alumina or supported ferric chloride or copper sulfate, Yb(OTf)3 and TS-1 have revealed great promise in this area. We modified nano silica gel surface by using thionyl chloride, which acts as a mild and efficient catalyst, and can be a useful and cheap catalyst for the synthesis of β-amino alcohols. Our studies have shown that thionyl chloride is a satisfactory chlorinating agent for nano silica and amorphous silica, if used undiluted. The extent of reaction with thionyl chloride gives values for active silanols per unit area of silica surface, comparable to other method, for determining available activities. Nano silica chloride was prepared by the readily available material and can also be easily removed from the reaction mixture.