The tautomeric binary system consisting of N-(3,4-dimethyl-5-isoxazolyl)-4-amino-l,2-naphthoquinone (1), m.p. 156~ and 2-hydroxy-N-(3,4-dimethyl-5-isoxazolyl)-l,4-naphthoquinon-4-imine (2), m.p. 218~ was studied by DTA-TG-DTG and IR spectrometry. Crystals of 1, left in contact with their mother liquor during 4 months, exhibited thermal behaviour similar to that of physical mixtures of 1 and 2, which reveal the presence of a eutectic at about 146~The effects of light, heat and humidity on the stabilities of 1 and 2 were also studied. Heat (up to 110~ did not induce any change observable by DTA-TG-DTG in either 1 or 2. Moisture and daylight affected only 1. Upon melting, interconversion of the isomers was not observed.
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