Oxalic acid is an organic compound with the chemical formula H2C2O4. It is a dicarboxylic acid, and is a reducing agent. Oxalic acid exists in two forms depending on the hydrogen bonding: a chain-like structure or a sheet-like structure. The anhydrous form of oxalic acid is both acidic as well as hydrophilic.
It occurs in nature in wood-sorrels, spinach (broccoli, cabbage, and Brussels sprouts), Rhubarb leaves and parsley. Some bacteria produce oxalic acid through the oxidation of carbohydrates. Plants that belong to a genus called fenestraria produce crystalline oxalic acid to help in transmitting light for photosynthesis.
General properties of oxalic acid are:
- Oxalic acid is a colourless liquid.
- Oxalic acid is crystalline in structure.
- Oxalic acid is soluble in water.
Production of Oxalic Acid:
Oxalic acid is manufactured by the oxidation of carbohydrates or glucose using nitric acid or air, in the presence of a catalyst (vanadium pentoxide) for commercial use. The raw materials used for the production can be molasses/cellulosic wastes and nitric-sulphuric acid mixture.
The process starts with a batch process, where the nitric acid is added to the molasses or cellulosic wastes. This mother liquor is then fed to a reactor and sulphuric acid is added to increase the temperature of the reactor. There are cooling coils present, through which a coolant is circulated to reduce the temperature. Then nitric acid is added into the reactor, followed by the gradual addition of sugar.
The rate of adding sugar is increased gradually, to avoid rapid increase in the temperature. The oxalic acid that is formed, is centrifuged and then purified by recrystallization using water. The recrystallized product is further centrifuged and dried. The reaction can be written as below:
C6H12O6 + 6HNO3 → 3H2C2O4 + 6NO + 2H2O
Oxalic acid has various applications across many industries. Some of the applications are:
Oxalic Acid is best used as a wood bleaching agent. Wooden furniture turn dark grey on being exposed to air, oxalic acid is used to bleach the surface to lighten these spots. Oxalic acid is used in the refinishing of these furniture, to lighten the areas that have become darker due to exposure to water.
Oxalic Acid is used as a bleaching agent in the textile industry. It is used as a mordant in the dyeing process. It aids by forming a coordination complex with dyes and setting the dyes on fabrics and cellulosic.
As oxalic acid is an iron complexing agent, it is used in the removal of rust during metal treatment, used as a commercial rust remover to remove rust from tubs, sinks, plumbing fixtures, etc.
Paper and Pulp Industry
It is used as a bleaching agent to bleach the pulp during paper making.
Oxalic acid is used by pharmaceutical industry to manufacture antibodies such as tetracycline, phenobarbital, oxytetracycline and aureomycin. It is also used in the manufacturing of borneol, which is an important ingredient for Chinese medicines, precursor to perfume, antiseptics, as well as cosmetics and personal care products.
Oxalic acid is used as a precipitating agent in earth mineral processing. It is used as a purifying agent in the pharmaceutical industry, in waste water treatment to remove calcium from water, in marble polishing as a grinding agent and to sterilize home brewing equipment. It is also used as a reducing agent for photography and ink removal.
|PHYSICAL AND CHEMICAL PROPERTIES (DIHYDRATE)|
|PHYSICAL STATE||White crystals|
|MELTING POINT||101 – 102 C|
|BOILING POINT||149 – 160 C (sublimes)|
|SPECIFIC GRAVITY||1.6 – 1.7|
|SOLUBILITY IN WATER||1g/7ml|
|NFPA RATINGS||Health: 3; Flammability: 1; Reactivity: 0|
|FLASH POINT||163 C|
|STABILITY||Stable under ordinary conditions|
|HANDLING AND STORAGE|
|Keep in a tightly closed container. Protect from physical damage. Store in a cool, dry, ventilated area away from sources of heat, moisture and incompatibilities. Containers of this material may be hazardous when empty since they retain product residues (dust, solids); observe all warnings and precautions listed for the product.|
|FIRST AID MEASURES|
Remove to fresh air. If not breathing, give artificial respiration. If breathing is difficult, give oxygen. Call a physician immediately.
DO NOT INDUCE VOMITING! Give large quantities of limewater or milk to drink. Never give anything by mouth to an unconscious person. Call a physician immediately.
In case of contact, wipe off excess from skin then immediately flush skin with plenty of water for at least 15 minutes while removing contaminated clothing and shoes. Wash clothing before reuse. Call a physician immediately.
Immediately flush eyes with gentle but large stream of water for at least 15 minutes, lifting lower and upper eyelids occasionally. Call a physician immediately.
|FIRE FIGHTING MEASURES|
Oxalic Acid is a combustible solid below 101C (215F)
Reacts explosively with strong oxidizing materials and some silver compounds.
Fire Extinguishing Media:
Water spray, dry chemical, alcohol foam, or carbon dioxide. Foam or water on molten oxalic acid may cause frothing. Water spray may be used to keep fire exposed containers cool.
In the event of a fire, wear full protective clothing and NIOSH-approved self-contained breathing apparatus with full face piece operated in the pressure demand or other positive pressure mode.
|ACCIDENTAL RELEASE MEASURES|
|Remove all sources of ignition. Ventilate area of leak or spill. Wear appropriate personal protective equipment as specified in Section 8.Spills: Clean up spills in a manner that does not disperse dust into the air. Use non-sparking tools and equipment. Pick up spill for recovery or disposal and place in a closed container. Remove unnecessary people. If material comes in contact with water, neutralize liquid with alkaline material (soda ash, lime), then absorb with an inert material (e.g. vermiculite, dry sand, earth) and place in a chemical waste container. Do not use combustible materials, such as saw dust. Do not flush to sewer.|