Isatin (Indole-2,3-dione, 2:3-Indolinedione, CAS# 91-56-5) forms yellow-red crystalline needles and melts to a yellow liquid at about 200C. It is an important raw material for dye manufacture (artificial indigo, disperse dye yellows) and is used for the manufacture of pharmacuticals. Images tones inverted and adjusted.