2-oxo-2H-pyran-5-carboxylic acid 2H-pyran-5-carboxylic acid, 2-oxo- 500-05-0 Coumalic Acid InChI=1/C6H4O4/c7-5-2-1-4(3-10-5)6(8)9/h1-3H,(H,8,9