Indian Journal of Chemistry Vol. 47B, October 2008, pp. 1545-1548 An efficient use of microwave-superoxide combination for the synthesis of organic carbamates and dithiocarbamates Satish Kumar Singh, Manjusha Verma & Krishna Nand Singh* Department of Chemistry, Faculty of Science, Banaras Hindu University, Varanasi 221 005, India E-mail: knsinghbhu@yahoo.co.in Received 12 February 2008; accepted (revised) 4 July 2008 The present report demonstrates an efficient use of microwave-tetraethylammonium superoxide combination under non-aqueous conditions to bring about a mild and safe carbamation/thiocarbamation of amines, using carbon dioxide/carbon disulfide and methyl iodide. Keywords: Carbamate, dithiocarbamate, superoxide, microwave Organic carbamates and dithiocarbamates have attracted a great deal of importance due to their interesting chemistry and wide utility 1-7 . Although a number of methodologies have been developed, the standard preparation of carbamates/dithiocarbamates generally involves the use of toxic and highly reactive phosgene/thiophosgene 8 and its derivatives 9 , thereby posing environmental and safety problems. As a result, considerable effort has been made to develop a phosgene/thiophosgene free route 10 for the preparation of carbamates and thiocarbamates. However, many of these methods suffer from limitations, such as long reaction times, use of expensive and strongly basic reagents, use of volatile solvents, tedious work-up, and low yields 11 . Prompted by the current use of microwave (MW) irradiation in organic synthesis 12 and due to the interest on superoxide organic chemistry 13 , it was thought worthwhile to explore the role of MW- superoxide combination to achieve an efficient synthesis of carbamates and dithiocarbamates via a three-component coupling of an amine, CO 2 /CS 2 and methyl iodide (Schemes I and II). In order to optimize the yield of products, the effects of various parameters such as molar proportion of the reactants, Watt (160, 320, 480, 640 & 800) and irradiation time were studied in detail using the substrate 1a as reference. Under the optimized MW irradiation [160W], various amines 1a-f underwent smooth coupling with CO 2 in the presence of tetraethylammonium superoxide (Et 4 NO 2 ) in 5 to 7 minutes to afford the incipient carbamate anion. The amines 1a, 1b, 1f and 1g-m, however, underwent reaction with CS 2 /Et 4 NO 2 under MW at 320W in 3 to 7 minutes to give the dithiocarbamate anion, in dry DMF. Addition of methyl iodide and subsequent quenching with cold brine solution at room temperature readily furnished the methyl ester of carbamate 2 or dithiocarbamate 3 in fairly good yields (Tables I and II). It is important to mention that superoxide alone in the absence of MW was able to achieve the same transformation in considerably longer reaction time (2.5 hr) with 1a. To observe the sole role of MW on the above reactions, some blank experiments under microwave irradiation in the absence of Et 4 NO 2 were also carried out resulting in no net reaction. However when MW is coupled with superoxide ion, the rate of reaction is dramatically enhanced, thereby highlighting the significance of MW-superoxide combination. All the products were identified by their physical data, IR and NMR spectra, which were in conformity with their structures. Experimental Section IR spectra were recorded on a Jasco FT/IR-5300 spectrophotometer. 1 H NMR was run on a Jeol AL300 FT-NMR spectrometer. The chemical shifts are given in ppm with respect to TMS as internal standard. The TLC spots were detected using iodine chamber. All commercially available chemicals were purchased from Aldrich and Merck. Dry DMF from Aldrich was stored over molecular sieves (4Å) prior to use. Crude products were purified by column chromatography.