Oxalic acid is a colorless crystalline compound with two carboxylic groups. Due to the presence of two carboxyl groups, oxalic acid is a strong acid and it is also a reducing agent. Oxalic acid is present in many fruits and vegetables in the form of oxalates.
Oxalic acid is produced by oxidation of carbohydrates in the presence of a catalyst like nitric acid or air in vanadium pentoxide. Another method involves oxidation and carbonylation of alcohols resulting in esters, followed by hydrolysis to yield oxalic acid.
4ROH + 4CO + O2 --> 2 (CO2R)2 + 2H2O