ChemInform Abstract: A New Modified Synthetic Method for Preparation of N,N-Dichlorocarbamates

N-chloro compounds have been extensively exploited, both for fundamental research and a wide range of industrial applications, owing to their easy handling, commercial availability and high storage stability. As a result, intensive research and studies have been carried out over a long period of time on their chlorination, oxidation, water disinfection and some other applications 1-8 in synthetic organic chemistry 9 . N-Chloro compounds have also been employed for decontamination of chemical warfare agents 10,11 . N, NDichlorocarbamate was prepared by Dutta and Gupta 12 and subsequently by Houben 13 and by Chabrier 14 but explicit details concerning yield, methods of isolation and purity and physical characteristics of products was not reported. A major drawback of the Foglia and Swern 15 method was passage of chlorine gas for an extended period at RT, which can result in inhalation toxicity. White and Kovaic 16 have also reported low yields and time consuming processes for the synthesis of N,Ndichlorocarbamate and also difficulties in isolation of pure N,N-dichlorocarbamate. These limitations prompted the development of a rapid and efficient synthetic procedure for N, Ndichlorocarbamate that involves easy work-up and quantitative yields with shorter reaction times by making use of calcium hypochlorite. In this paper is reported an improved method, which results in high yield in shorter time to give pure N,Ndichlorocarbamate in acidic medium without using any volatile solvents for extraction. Calcium hypochlorite is a versatile and very safe reagent for Nchlorination of substituted carbamates as compared to other reagents like sodium hypochlorite and chlorine gas. This reagent is commercially available, cheap, has high chlorine content and storage stability. Synthesis of all other hypochlorites involve passage of chlorine gas either into aqueous solution of sodium hydroxide or tert-butyl alcohol for extended periods, which result in inhalation toxicity and difficulties in handling and work-up procedures. Due to the high chlorine content of Ca(OCl)2 (6070%) as compared to NaOCl (4-12%), a lesser quantity of the reagent is able to convert a larger portion of the substituted carbamates into N,Ndichlorocarbamates with high yields in less time. Calcium hypochlorite is a commercially available compound that produces positive chlorine in aqueous medium for N-chlorination of carbamate. It was found that for chlorination of carbamates, an acidic medium is required to avoid the formation of salt of monochlorocarbamates. In this procedure, the carbamates was first suspended in acetic acid and the reaction mixture cooled to 0-5°C with stirring till the starting material dissolved completely. To this mixture, an aqueous solution of calcium hypochlorite was added slowly in 10 min with stirring. Acetic acid was added in portions to bring the pH of the mixture to acidic condition. After 15 min, a translucent yellow organic layer was well separated in aqueous medium. Acetic acid was used for complete dissolution of calcium hypochlorite in aqueous medium and also used as a solvent and to maintain acidic pH of the reaction mixture. The reaction of various substituted alkyl and aryl carbamates (Entry 1-8) with calcium hypochlorite afforded corresponding N,N-dichlorocarbamates in