Oxalic acid

Some plants make a special juice.

This juice is found in spinach and broccoli. It is also in rhubarb leaves. It can be found in starfruit too.

This juice can help clean things. It is used to wash away rust. It is also used to make teeth white.

Some tiny bugs make this juice in the dirt. It helps them find food in the soil.

Be careful with this juice. It can hurt your skin if it is strong. Eating too much can make you sick.

Can you find it in your food?

Oxalic acid is a white, solid substance. It is found in many plants.

Early scientists found it in wood-sorrel plants. This is why it has its name. You can find it in many foods. Spinach and broccoli have it. Rhubarb leaves and starfruit have it too. Even citrus juice has a small amount. Some tiny bugs in your gut help break it down.

This acid is useful for cleaning. It is very good at removing rust. It works by making a salt with iron. This salt can dissolve in water. People also use it to whiten teeth. It is used in some dyes and bleaches. Some beekeepers use it to help bees.

But you must be careful. Eating too much can be toxic. Strong versions can cause chemical burns on your skin. In nature, some fungi use it to get nutrients from the soil. Some plants even use crystals of it to move light. Scientists are now studying ways to use it to catch carbon dioxide.

Oxalic acid is a special kind of organic acid. It looks like a white, crystalline solid. When you mix it with water, it turns into a clear liquid. This acid is quite strong compared to other common acids like acetic acid. You might find it in your food or used in a cleaning bottle. It is very useful for many jobs, but it can be toxic if eaten in large amounts. Even concentrated versions can cause chemical burns on your skin.

This acid works in many interesting ways. It acts as a reducing agent, which helps in certain chemical reactions. It is also a chelating agent. This means it can grab onto metal ions, like tiny pieces of metal, and hold them. Because of this, it is great at removing rust. It turns iron into a special salt called a ferrioxalate ion. This salt can dissolve easily in water, so the rust just washes away. It can also be used to whiten teeth or help make dyes.

People have been studying this acid for a very long time. In 1745, a Dutch scientist named Herman Boerhaave found a salt from wood-sorrel plants. Later, in 1773, François Pierre Savary isolated the acid itself from those same plants. In 1776, Swedish chemists Carl Wilhelm Scheele and Torbern Olof Bergman made it by reacting sugar with nitric acid. Scheele even called it "sugar acid" at first. By 1824, a German chemist named Friedrich Wöhler made it by reacting cyanogen with ammonia. This was one of the first times a person made a natural product in a lab.

Today, we produce about 120,000 tonnes of oxalic acid every year. Most of it is made in big factories by using nitric acid on carbohydrates like glucose. Some factories use a method with oxygen to help the process work. You can find this acid in many places in nature. Spinach, broccoli, and cabbage all have it. Rhubarb leaves and starfruit have it too. Even some plants, like the Virginia creeper, make it in their sap.

Nature uses oxalic acid in ways that might surprise you. Some fungi in the soil use it to help find nutrients. Some plants, called Fenestraria, even use crystals of it to act like tiny glass fibers. These fibers help move light to parts of the plant that need it. In your own body, a tiny bacterium called Oxalobacter formigenes helps break the acid down. Scientists are even looking at ways to use it to catch carbon dioxide from the air. It is a small molecule that does very big things.

Oxalic acid is a powerful organic acid with the chemical formula H2C2O4. It is also known by its systematic name, ethanedioic acid. As the simplest dicarboxylic acid, it possesses two carboxyl groups in its structure. This acid typically appears as a white, crystalline solid. When dissolved in water, it forms a completely colorless solution. It is significantly stronger than acetic acid, which is the acid found in vinegar. Because of its chemical properties, it is used in many industrial and household tasks. However, it can be toxic if consumed in large amounts. Contact with highly concentrated forms can also cause chemical burns on the skin.

The chemical behavior of oxalic acid is driven by its ability to act as a reducing agent. It is also a highly effective chelating agent. A chelating agent is a molecule that can bind to metal cations, which are positively charged metal ions. This ability is why oxalic acid is so useful for cleaning rust. When it meets rust, it reacts with the ferric iron to form a ferrioxalate ion. This specific ion is water-soluble, meaning it dissolves easily in water. This allows the rust to be washed away during the cleaning process. This same mechanism makes it an active ingredient in products like Bar Keepers Friend.

Oxalic acid exists in several different forms depending on its environment. In its most common natural state, it occurs as a dihydrate, written as H2C2O4·2H2O. This means two molecules of water are attached to each molecule of acid. When the water is removed, it becomes anhydrous oxalic acid. This anhydrous form can exist in two different structural patterns, known as polymorphs. In one pattern, hydrogen bonding creates a chain-like structure. In the other pattern, the hydrogen bonding creates a sheet-like structure. Because the anhydrous version is both acidic and hydrophilic, it is often used in chemical processes called esterifications.

Humans have been studying this substance for nearly three centuries. In 1745, the Dutch botanist Herman Boerhaave isolated a salt from wood-sorrel plants. In 1773, François Pierre Savary successfully isolated the acid itself from those same sorrel salts. A few years later, in 1776, Swedish chemists Carl Wilhelm Scheele and Torbern Olof Bergman created the acid by reacting sugar with concentrated nitric acid. Scheele originally called this substance "sugar acid." By 1784, Scheele proved that this "sugar acid" was the same as the acid found in nature. The modern name we use today was established in 1787 by de Morveau, Lavoisier, and their colleagues. In 1824, Friedrich Wöhler performed a landmark experiment by reacting cyanogen with ammonia to create the acid. This was one of the first times a scientist synthesized a natural product in a laboratory.

Industrial production of oxalic acid is a massive global operation. Approximately 120,000 tonnes of the acid are produced every year. Most modern production involves the oxidation of carbohydrates, such as glucose. This is often done using nitric acid or air in the presence of a catalyst called vanadium pentoxide. Other industrial methods involve using oxygen to regenerate nitric acid from precursors like ethylene glycol. Historically, workers produced it by treating sawdust with strong bases like sodium hydroxide. Today, the acid serves many roles, including use as a mordant in dyeing processes. About 25% of all produced oxalic acid is used for this purpose. It is also used in the semiconductor industry to help polish copper layers.

Oxalic acid is found throughout the natural world in many different organisms. It is highly concentrated in the spinach family and brassicas, such as broccoli and cabbage. It is also present in rhubarb leaves, which contain about 0.5% oxalic acid. Some plants, like the Virginia creeper, produce oxalate crystals in their sap. In a fascinating biological twist, plants in the genus Fenestraria create optical fibers from crystalline oxalic acid. These natural fibers transmit light to parts of the plant that live underground for photosynthesis.

In the human body, the acid plays a complex role in health and biology. A specific bacterium in the human gut, called Oxalobacter formigenes, helps to break down oxalate. This helps prevent the acid from building up in the system. Scientists are also studying how oxalic acid might interact with cancer cells. The acid can inhibit an enzyme called lactate dehydrogenase (LDH). This enzyme is important for how certain cells create energy. Because some cancer cells rely heavily on this specific energy process, inhibiting the enzyme is a potential area for medical research. Furthermore, researchers are investigating ways to use electrocatalysis to turn carbon dioxide into oxalic acid, which could help with carbon capture efforts.