In organic chemistry, indoxyl is a nitrogenous substance with the chemical formula: C<sub>8</sub>H<sub>7</sub>NO. Indoxyl is isomeric with oxindol and is obtained as an oily liquid.
The Heumann indigo synthesis starts from anthranilic acid:
In nature indoxyl is derived from indican, which is a glycoside. The hydrolysis of indican yields ò-D-glucose and indoxyl.
Indigo dye is a product of the mild oxidation of indoxyl.
Indoxyl can be found in urine and is titrated with Obermayer's reagent, which is a dilute solution of ferric chloride (FeCl<sub>3</sub>) in hydrochloric acid (HCl).