Urea and Polyurea Production: An Innovative Solvent- and Catalyst-Free Approach through Catechol Carbonate

Abstract

The peculiar reactivity of catechol carbonate (CC) with amines and polyamines in both solvent-and catalyst-free conditions is herein described. In all the tests performed at room temperature, CC conversion reached 100% in a few seconds leading to the selective formation of the corresponding 2hydroxyphenylcarbamate. This compound is further rapidly converted to the disubstituted urea by the consecutive nucleophilic attack of another amine. Noteworthy, the application of this approach can be successfully extended to the one-pot bioaminebased synthesis of polyurea as herein proposed for the first time in the literature. The reaction is of general purpose for primary amines, and catechol can be easily recovered by sublimation as pure crystals ready to be recycled for the synthesis of new CC. An exception is related to the reactivity of secondary amine, which leads to the selective formation of substituted phenolic carbamates (e.g., 2-hydroxyphenyl diethylcarbamate), suitable as intermediates in medicinal chemistry.

Direct synthesis of polyureas from the dehydrogenative coupling of diamines and methanol

“…30 Expanding on the vision of the methanol economy, we also present here the synthesis of a new renewable polyurea from the dehydrogenative coupling of a bio-sourced diamine with methanol that can be renewable. Furthermore, using 13 CH 3 OH we have also demonstrated the first synthesis of 13 C-labelled polyureas which may have potential applications in drug delivery, 31-33 13 C-MRI, 34 and in assessing the environmental impacts of plastics. 35 We started our investigation by exploring optimum conditions for the dehydrogenative coupling of diamines and methanol in the presence of ruthenium-Macho catalyst 1 which in the past has exhibited excellent activity for dehydrogenation of methanol 36 and the dehydrogenative synthesis of urea derivatives.…”

“…[2][3][4][5][6][7] Although the use of CO 2 for the synthesis of polyureas is attractive, the use of harsh reaction conditions such as reaction temperature of 170-180 1C, and CO 2 pressure of 40-110 bars, in order to overcome the high thermodynamic barriers, present a bottleneck to utilize this methodology on an industrial level. Another approach is based on the polycondensation of diamines with CO 2 derivatives -organic carbamates, [8][9][10][11][12] organic carbonates [13][14][15] and urea (NH 2 CONH 2 ). 16,17 This methodology also suffers from drawbacks such as the use of expensive reagents or solvents (e.g.…”

“…biscarbamate [8][9][10][11][12] or ionic liquids as solvent), poor substrate scope, [14][15][16][17] and low atom-economy. 13 Catalytic dehydrogenation is a green and atom-economic approach in organic synthesis, and several new green protocols based on acceptorless dehydrogenative coupling have been developed in the past. 18 For example, in relevance to the current report, the synthesis of urea derivatives has been reported by the catalytic dehydrogenative coupling of methanol and amines, independently by the groups of Hong, 19 Gunanathan, 20 Bernskoetter, 21 and Milstein.…”

“…Furthermore, we envisioned that the current methodology could allow us to synthesize the first 13 C-labelled polyurea using 13 CH 3 OH. Polyureas have potential applications as drug carriers 32 for drug delivery, and a labelled polymer can offer a new tool to study the fate of such drug carriers.…”

“…Polyureas have potential applications as drug carriers 32 for drug delivery, and a labelled polymer can offer a new tool to study the fate of such drug carriers. 31,33 Moreover, 13 C-labelled polymers have been utilized for 13 C-MRI, 34 and to study the environmental impact of microplastics. 35 It is noteworthy that synthesis of a 13 C-labelled polyurea from the previously reported methods would be very challenging and expensive due to the unavailability of a 13 C-labelled diisocyanate.…”