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Solid-state synthesis and isolation of reactive intermediates using mechanochemistry: the synthesis of aromatic N-thiocarbamoylbenzotriazoles

Recent advancements in the development of solid-state synthetic methodology and crystal engineering have brought forward mechanochemistry1 as an environmentally-friendly alternative to achieve clean, solvent-free and low-energy chemical synthesis. Following our interest in the synthesis of complex non-symmetrical (thio)ureas by ball milling, 2 this contribution will present our latest results on the selective and quantitative approach for the synthesis of non-symmetrical molecules, involving aromatic intermediates 2 derived from methanethione 1 as a thiocarbamoylation reagent. Surprisingly, whereas N-thiocarbamoylbenzotriazoles 2 are known to be inaccessible, short-lived intermediates in solution-based syntheses of thioureas, 3 in the solid-state mechanochemical environment they can be obtained as bench-stable solids. Indeed, excellent control over stoichiometry of the reactant mixture under mechanochemical conditions enables the efficient synthesis of non-symmetrical aromatic N-thiocarbamoylbenzotriazoles 2 in �~I�98% isolated yields. Further mechanochemical reactions of 2 with amines afford (non)symmetrical thioureas in 90-95% yields. Due to the sensitivity of 2 in solution, which was confirmed by 1H NMR in CDCl3, their structural features have been assesed through solid-state analytical methods such as CP-MAS 13C/15N NMR, FTIR-ATR, TG/DSC and structure determination from X-ray powder diffraction data.

mechanochemistry

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