Oxalic+Acid

An organic compund that is a colorless crystalline solid. It is a dicarboxylic acid with the formula of: H2C2O4
 * Oxalic Acid:**

Oxalic Acid is about 3,000 times stronger than acetic acid and it is a reducing agent and its conjugate base, known as oxalate is a chelating agent for metal cations.

Oxalic acid is mainly manufactured by the oxidation of carbohydrates or glucose using nitric acid or air in the presence of vanadium pentoxide. A variety of precursors can be used including glycolic acid and ethylene glycol. A newer method entails oxidative carbonylation of alcohols to give the diesters of oxalic acid

4 ROH + 4 CO + O2 → 2 (CO2R)2 + 2 H2O

These diesters are subsequently hydrolyzed to oxalic acid. Approximately 120,000 metric tons are produced annually.

Although it can be readily purchased, oxalic acid can be prepared in the laboratory by oxidizing sucrose using nitric acid in the presence of a small amount of vanadium pentoxide as a catalyst. The hydrated solid can be dehydrated with heat or by azeotropic distillation. Of historical interest, Wöhler prepared oxalic acid by hydrolysis of cyanogen in 1824. This experiment may represent the first synthesis of a natural product.

Oxalic __acid__ is naturally found in some foods. Oxalic acid combines with metals such as calcium in the body to form oxalate crystals which can irritate the gut and kidneys. The most common kind of kidney stone is made of calcium oxalate. Since oxalic acid binds vital nutrients such as calcium, long–term consumption of foods high in oxalic acid can lead to nutrient deficiencies. Healthy individuals can safely consume such foods in moderation, but those with kidney disorders, gout, __osteoporosis__ or rheumatoid arthritis are typically advised to avoid foods high in oxalic acid or oxalates.

=Uses=

Oxalic acid is a chemical that can be a dangerous in high doses but not in moderate levels. It is a naturally occurring component of plants such as rhubarb and buckwheat, and it is usually found in somewhat high levels in dark green leafy foods, though not high enough to cause harm to those ingesting it.

Woodwork
Oxalic acid is best known as an agent in wood bleaching. After long periods of exposure to sun and weather, wood can turn gray. By rubbing oxalic acid on the affected wood, you can lighten its gray appearance. Furniture refinishers also use oxalic acid after stripping wood to lighten darker-stained areas before refinishing.

Cleaning Agent
Oxalic acid also is a popular cleaning agent. For instance, it is used to clean and sterilize home brewing equipment used to make beer and wine. It also is used as a purifier in the pharmaceutical industry and by rock collectors to clean various minerals and related specimens. And it works well at removing hard water stains from tile and plumbing fixtures. Rust Remover Oxalic acid can be used to remove rust stains from kitchen counter tops, plumbing pipes and even fabric. It is used in commercial rust removers to eliminate rust stains from tubs, sinks and tile, as well as from metal.

Other Uses
Oxalic acid has many other uses as well. It can be used as precipitating agent in rare-earth mineral processing, as a bleaching agent in textile production and as a grinding agent in tasks such as polishing marble. Plus, it's also used in the treatment of wastewater, because oxalic acid helps remove calcium from water. It even can be used as a reducing agent for photography.

Warning
When purified, oxalic acid is very corrosive and toxic. You should use latex gloves, a dust mask and eye protection at all times while using oxalic acid, and you should always mix and use it in a well-ventilated area. Do not induce vomiting if ingested; instead drink plenty of milk or water and contact a poison control center immediately.

Preparation
Oxalic acid is mainly manufactured by the oxidation of carbohydrates or [|glucose] using [|nitric acid] or air in the presence of [|vanadium pentoxide]. A variety of precursors can be used including [|glycolic acid] and [|ethylene glycol]. [|[3]] A newer method entails oxidative [|carbonylation] of [|alcohols] to give the diesters of oxalic acid: 4 ROH + 4 CO + O2 → 2 (CO2R)2 + 2 H2O These diesters are subsequently hydrolyzed to oxalic acid. Approximately 120,000 [|metric tons] are produced annually. [|[4]]

Structure
Anhydrous oxalic acid exists as two [|polymorphs] ; in one the [|hydrogen-bonding] results in a chain-like structure whereas the hydrogen bonding pattern in the other form defines a sheet-like structure. [|[7]] Because the anhydrous material is both acidic and [|hydrophilic] (water seeking), it is used in [|esterifications].

Reactions
Oxalic acid is a relatively strong acid, despite being a [|carboxylic acid] : C2O4H2 → C2O4H− + H+; pKa = 1.27C2O4H− → C2O42− + H+; pKa = 4.27 Oxalic acid undergoes many of the reactions characteristic of other carboxylic acids. It forms esters such as [|dimethyl oxalate] ( [|m.p.] 52.5–53.5 °C). [|[8]] It forms an acid chloride called [|oxalyl chloride]. Oxalate, the conjugate base of oxalic acid, is an excellent [|ligand] for metal ions, e.g. the drug [|oxaliplatin]. Oxalic acid and oxalates can be oxidized by [|permanganate] in an [|autocatalytic] reaction. [|[9]]