Abstract:
1,3-Bis(m-nitrophenyl)urea (MNPU) was identified as having three different nonsolvated polymorphs (α form, yellow prisms; β and δ forms, white needles), one monohydrate (γ form, yellow plates) and many others as cocrystal complexes with various hydrogen bond acceptors. When the main polymorphs were characterized by IR spectroscopy, major differences were noticed in their IR spectra: α has νC=O = 1710 cm-1, β has νC=O = 1660 cm-1, δ has νC=O = 1674 cm-1 and γ has νC=O = 1707 cm-1. While investigating the reactivity of some reagents as potential replacements of the toxic phosgene, we discovered that bis(o-nitrophenyl)carbonate (DONPC) can be efficiently used in the synthesis of symmetrical N,N`-diaryl ureas. MNPU, like other diaryl ureas synthesised by this method, was isolated from reaction mixture (solvent toluene) by precipitation. Here we report a study of polymorphic forms obtained directly from reaction mixture when DONPC was treated with m-nitroaniline under various conditions. The products were analysed by IR spectroscopy and optical microscopy and both α and β forms were shown to be obtained. Another form with a previously unreported IR spectrum was identified by analysing the precipitate formed under particular conditions.
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