Flame-Induced Addition of Urea to Unsaturated Carboxylic Acids

When a hydrogen-oxygen flame was blown against an aqueous solution of urea and maleic acid, N-carbamoylaspartic acid was generated. This compound seemed to be formed by the addition of an amidinoxyl radical to a C–C double bond of the acid, followed by a thermal rearrangement of an amidinoxy to a ureido group.