ISOXAZOLES, in chemistry, cyclic compounds containing a five-membered ring of three carbon atoms, one nitrogen atom, and one oxygen atom, the last two being adjacent to each other (see CHEMISTRY : Organic : Heterocyclic Division). They are prepared by eliminating water from the monoximes of 0-dike tones, 13-ketone aldehydes, or hydroxymethylene ketones (L. Claisen, 1891). Dimethylisoxazole (see I.), thus obtained from acetylacetone and hydroxylamine, is a colourless pungent liquid boiling at C at 76o mm.
This isoxazole can be nitrated by replacement of the hydrogen in position 4, and this nitro-compound reduced with amalgamated aluminium and moist ether yields 4-amino-3:5-dimethylisoxazole (II.), a base which resembles the aromatic primary amines in that
its hydrochloride and other salts are diazotizable (G. T. Morgan and H. Burgess, 1921). Its diazonium chloride is represented by (III.). These results indicate that the isoxazole ring has certain properties in common with the aromatic nuclei of benzene and its homologues.