Hydrogenoxalate

Hydrogenoxalate or hydrogen oxalate is an anion with chemical formula HC₂O₄ or HO₂C–CO₂, derived from oxalic acid by the loss of a single proton; or, alternatively, from the oxalate anion C₂O₄ by addition of a proton.

The name is also used for any salt containing this anion, such as NaHC₂O₄, KHC₂O₄, or NH₃HC₂O₄. Hydrogenoxalates may also be called (especially in older literature) binoxalates, acid oxalates, or monobasic oxalates.