Oxalic acid is an organic substance with the chemical formula H₂C₂O₄, which is a metabolite of living organisms, a binary weak acid, widely distributed in plants, animals and fungi, and plays different functions in different life forms. Studies have found that more than 100 kinds of plants are rich in oxalic acid, especially spinach, amaranth, sugar beet, purslane, taro, sweet potato and rhubarb and other plants have the highest content, because oxalic acid can reduce the bioavailability of mineral elements, and it is easy to form calcium ions in the human body Calcium oxalate leads to kidney stones, so oxalic acid is often considered as an antagonist of mineral element absorption and utilization. The anhydride is carbon trioxide.