Abstract
Silica sulfuric acid (SSA) was found to be an efficient heterogeneous catalyst for the synthesis of 1-substituted 1H-1,2,3,4-tetrazoles from the reaction of primary amines with triethyl orthoformate and sodium azide under thermal and solvent-free conditions.
Highlights
Application of the tetrazole compounds including 1substituted tetrazoles [1,2,3] has increased rapidly over the past few years for different purposes
1-substituted tetrazoles are generally synthesized by reaction of isocyanides with large excess amounts of dangerous and harmful hydrazoic acid [12, 13] or trimethyl azide [14]. e other methods include addition of amines or their salts to sodium azide and orthocarboxylic acid ester in acetic acid or tri uoroacetic acid [15, 16]
All of these known methods suffered from some limitations such as low yields, drastic reaction conditions, the use of expensive and toxic metal catalysts, tedious workup, complex isolation and recovery procedures, the use of excessive amounts of glacial acetic acid or tri uoroacetic acid, the use of high boiling point solvent such as DMF and even the need for excess amounts of dangerous and harmful hydrazoic acid [4, 6,7,8, 15, 16]. erefore, the development of a more efficient and convenient method for the synthesis of 1-substituted tetrazoles under solvent-free conditions still remains an active research area
Summary
Application of the tetrazole compounds including 1substituted tetrazoles [1,2,3] has increased rapidly over the past few years for different purposes. Su and coworkers have reported the synthesis of 1-substituted tetrazoles using Yb(OTf) in volatile organic solvents [17] All of these known methods suffered from some limitations such as low yields, drastic reaction conditions, the use of expensive and toxic metal catalysts, tedious workup, complex isolation and recovery procedures, the use of excessive amounts of glacial acetic acid or tri uoroacetic acid (an expensive solvent), the use of high boiling point solvent such as DMF (which is soluble in both organic solvents and water; its removing from the reaction mixture is difficult) and even the need for excess amounts of dangerous and harmful hydrazoic acid [4, 6,7,8, 15, 16]. Among various silica-based heterogeneous catalysts, silica sulfuric acid (SSA) has advantages of low cost, ease of preparation and recyclability, and is insoluble in all organic solvents
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