Communications to the Editor Bull. Korean Chem. Soc. 2012, Vol. 33, No. 7 2129 http://dx.doi.org/10.5012/bkcs.2012.33.7.2129 Silica Chloride-Catalyzed Microwave-Assisted Efficient and Selective One-Pot Synthesis of Amides from Aldehydes Bandita Datta and M. A. Pasha * Department of Studies in Chemistry, Central College Campus, Bangalore University, Bengaluru -560001, India * E-mail: m_af_pasha@ymail.com Received January 11, 2012, Accepted March 30, 2012 Key Words : Silica chloride, Aromatic aldehydes, Amides, Microwave reactor 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 carbox- ylic acid with an amine. The other alternative methods include Schotten-Baumann reaction, Beckmann rearrange- ment, Willgerodt reaction, Ugi reaction, Chapmann rearrange- ment, dehydrogenative acylation. Conversion of aldoximes to amides is present in the literature. 1 We also have carried out the inter-conversion of amides to nitriles and vice versa. 2 In recent years, solid-phase synthesis has become one of the most important tools in organic synthesis. Silica chloride is prepared by treating SOCl 2 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, 3 it can be used for different purposes. SiO 2 -Cl catalyzed protection of carbonyl com- pounds 4a and synthesis of amidoalkyl-2-naphthols 4b are well known reactions. Silica chloride is also used for the prepa- ration of other silica bonded reagents. 4c The extent of chlorination of the silica surface was determined by taking 1 g SiO 2 -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 SiO 2 . 3 In this communication, we report an improved and simple method for the synthesis of amides by a SiO 2 -Cl catalysed microwave-assisted reaction between an aromatic aldehyde and NH 2 OH·HCl at 100 W (Scheme 2). Experimental SiO 2 -Cl was prepared by the reported method. 3 Melting points were measured on a RAAGA (Indian make) apparatus. GC-Mass and IR spectra were recorded on a Shimadzu GC- MS QP 5050A and Shimadzu FT-IR-8400s instruments respectively. All the microwave reactions were conducted in a MILESTONE reactor at 100W. General Procedure for the Synthesis of Amides from Aldehydes. A mixture of aromatic aldehyde (2 mmol), NH 2 OH·HCl (2 mmol) and SiO 2 -Cl (0.1 g) was taken in a Pyrex glass tube, CH 3 CN (2 mL) was added, homogenized and placed in a microwave reactor at 100W for 3-4 min with 20 sec interval (Table 2). After completion of the reaction (TLC), EtOAc (5 mL) was added and the catalyst was removed by filtration, washed with warm ethanol and kept aside for reuse. The solvent was removed and the crude was subjected to silica gel column chromatography. Yields and the time taken are presented in Table 2. Results and Discussion Initially we found that, catalyst-free reaction did not occur when an aldehyde was treated with NH 2 OH·HCl under microwave irradiation at 100W. Later on aromatic aldehydes were treated with NH 2 OH·HCl in the presence of SiO 2 -Cl (200 mg, initially) and heated in a microwave reactor at 100W for 3-4 min (TLC). After work-up, the product was subjected to GC-Mass spectral analysis, which showed the formation of amides. Synthesis of nitriles from aldehydes in the presence of SiO 2 -Cl under microwave irradiation is reported by Das et al. 5 When we carried out the reaction of aldehydes and NH 2 OH·HCl at 100W in the presence of SiO 2 -Cl, we obtained only amides. We also noticed that, amides on irradiation with SiO 2 -Cl at 300W in a microwave reactor give nitriles, which is in agreement with the work of Das et al. It is clear from this study that, nitriles are formed through amide intermediates with catalytic SiO 2 -Cl. We wanted to optimize the amount of silica chloride used, hence, the reaction was carried out with different amounts of the catalyst, and the best result was obtained with 100 mg Scheme 1. Preparation of Silica chloride. Scheme 2. Synthesis of amides in the presence of SiO2-Cl.