N-Aryl substituted nitrogenoxosquaric acid (3-arylamino- 4-hydroxy-3-cyclobutenedione) is one of the very important intermediates for the preparation of asymmetric squaric acid derivatives. The study on synthetic method of preparation of monoamide of squaric acid is carried out. Surprisingly, during the reaction between a little excess oxosquaric acid and primary arylamine in water, we observed dehydration and have performed it. Seventeen N-arylnitrogenoxosquaric acid 3a～3q have been successfully synthesized, of which 3q appears phenomenon of thermotrophic colour. A possible reaction mechanism is discussed in accordance with the facts of reactions. Highly yielding, easily separating and puring are the merits of this synthetic method.

Key words: AROMATIC AMINES, AROMATIC AMINES, CYCLOBUTENE P, QUINOLINE P, SQUARIC ACID, PRIMARY AMINE, THERMOCHROMISM, DEHYDRATION REACTION, DIKETONE, ORGANIC SYNTHESIS