Silica Chloride-Catalyzed Microwave-Assisted Efficient and Selective One-Pot Synthesis of Amides from Aldehydes

Abstract

The amide function is ubiquitous in organic and biological chemistry. Amides are used as protecting groups in organic synthesis as they offer the advantages of very good stability to a wide range of conditions. They play an important role as technical polymers, pharmaceuticals, agrochemicals, peptides and proteins. Amides are formed by the reaction of a carboxylic acid with an amine. The other alternative methods include Schotten-Baumann reaction, Beckmann rearrangement, Willgerodt reaction, Ugi reaction, Chapmann rearrangement, dehydrogenative acylation. Conversion of aldoximes to amides is present in the literature. We also have carried out the inter-conversion of amides to nitriles and vice versa. In recent years, solid-phase synthesis has become one of the most important tools in organic synthesis. Silica chloride is prepared by treating SOCl2 with silica gel (Scheme 1). Due to its insolubility in organic solvents and the presence of labile Si-Cl bond which gives rise to Lewis acid centres, and nucleophile accepting property, it can be used for different purposes. SiO2-Cl catalyzed protection of carbonyl compounds and synthesis of amidoalkyl-2-naphthols are well known reactions. Silica chloride is also used for the preparation of other silica bonded reagents. The extent of chlorination of the silica surface was determined by taking 1 g SiO2-Cl in 25 mL boiled distilled water and titrated against 0.1N NaOH (9.3 mL). The amount of immobilized Cl has been found to be 0.93 miliquivalents/ g SiO2. 3