Hydrogen bonding of urea-salicylic acid, U·SA

Urea (U) and salicylic acid (SA) crystallize from aqueous solution as a 1∶1 adduct whose structure shows them to be linked via several weak and one strong hydrogen bonds. The ir spectra of the adduct and its deuterated counterpart have been analyzed and the stretching modes of the various hydrogen bonds identified. The1H and13C nmr. spectra are also interpreted to show that discrete adducts of U·SA persist in solution. On heating, U·SA decarboxylates at a much lower temperature than SA itself.