Highly Selective Phosgene-Free Carbamoylation of Aniline by Dimethyl Carbonate under Continuous-Flow Conditions

Over the last 20 years organic carbamates have found numerous applications in pesticides, fungicides, herbicides, dyes, pharmaceuticals, cosmetics, and as protecting groups and intermediates for polyurethane synthesis. Recently, in order to avoid phosgene-based synthesis of carbamates, many environmentally benign and alternative pathways have been investigated. However, few examples of carbamoylation of aniline in continuous-flow apparatus have been reported. In this work, we report a high-yielding, dimethyl carbonate (DMC)-mediated carbamoylation of aniline in a fixed-bed continuously fed reactor employing basic zinc carbonate as catalyst. Several variables of the system have been investigated (i.e. molar ratio of reagents , flow rate, and reaction temperature) to optimize the operating conditions of the system

Linear and cyclic carbamates via dialkyl carbonate chemistry

Dialkyl carbonates (DACs) as reagents have found recent application in phosgene-free synthesis of both linear and cyclic carbamates. Different type of catalysts have been investigated for the carbamoylation of aniline via dimethyl carbonate (DMC) in batch. The possibility of conducting this reaction in a fixed bed continuously fed reactor has been investigated. DACs have also been employed in a novel green approach to six-membered cyclic carbamates (1,3-oxazolidin-2-ones). Reaction of primary amines or hydrazines with bis(methyl carbonate) derivatives of 1,3-propandiols in the presence of potassium tert-butoxide resulted in the synthesis of several 1,3-oxazolidin-2-ones in good yield. These compounds can also be prepared by a one-step intermolecular cyclization where the 1,3-bis(methyl carbonate) intermediate is formed in situ.Dialkyl carbonates (DACs) as reagents have found recent application in phosgene-free synthesis of both linear and cyclic carbamates. Different types of catalysts have been investigated for the carbamoylation of aniline via dimethyl carbonate (DMC) in batch. The possibility of conducting this reaction in a fixed-bed continuously fed reactor has been investigated. DACs have also been employed in a novel green approach to six-membered cyclic carbonates (1,3-oxazolidin-2-ones). Reaction of primary amines or hydrazines with bis(methyl carbonate) derivatives of 1,3-propanediols in the presence of potassium tert-butoxide resulted in the synthesis of several 1,3-oxazolidin-2-ones in good yield. These compounds can also be prepared by a one-step intermolecular cyclization where the 1,3-bis(methyl carbonate) intermediate is formed in situ