Mechanistic studies in the chemistry of urea. Part 10. Reaction of urea and 1,3-dimethylurea with cyclohexane-1,2-dione and of imidazolidin-2-one (ethyleneurea) with several α-diketones

Abstract

Products formed by the reaction of cyclohexane-1,2-dione (1) with urea and with 1,3-dimethylurea in an acid medium have been examined. Compounds with ten-membered rings, (3a and b), are formed in both reactions. In strongly acid solution both (3a and b) form highly coloured products by protonation of the hydroxy-groups and loss of water. This identifies the chromophore in a colorimetric procedure using the oxime of cyclohexane-1,2-dione (nioxime), for the determination of urea concentrations. The cyclic urea imidazolidin-2-one (2) does not give isolable products on reaction with benzil and 1-phenylpropane-1,2-dione. With diacetyl polymeric material forms. However, a compound containing a ten-numbered ring (8) does form, in good yield, on reaction with cyclohexane-1,2-dione.