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Oxalic Acid: The Dicarboxylic Acid That Makes Rhubarb Leaves Toxic

Oxalic Acid: The Dicarboxylic Acid That Makes Rhubarb Leaves Toxic

{{Oxalic acid}} is the simplest dicarboxylic acid, found naturally in many plants, and is the nephrotoxin responsible for the toxicity of {{rhubarb}} leaves.

Oxalic acid (formula H2C2O4 or (COOH)2) is the simplest dicarboxylic acid — a white, odorless crystalline solid. It occurs naturally in many plants, including rhubarb leaves (about 0.5%), spinach (0.65-1.3%), Swiss chard, sorrel, parsley, amaranth, and wood-sorrel. It is a nephrotoxin (kidney toxin). Its mechanism of harm is precipitation of solid calcium oxalate, which can cause kidney failure, and it also drives mitochondrial dysfunction; ethylene glycol poisoning is dangerous in part because the body metabolizes it into oxalic acid. The reported lethal oral dose is roughly 15 to 30 grams. The practical food-safety point is the concentration difference within rhubarb: leaves contain substantially more oxalic acid (~0.5%) than the edible stalks (~0.2%), which is why rhubarb stalks are a common food while the leaves are discarded as poisonous. Industrially, about 120,000 tonnes are produced annually, largely by oxidizing carbohydrates with nitric acid.

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Chemistry

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92%

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May 29, 2026

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