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Introduction of Ascorbic Acid and L-Ascorbic Acid

View: 63 Author: Site Editor Publish Time: 2022-04-08 Origin: site

Ascorbic acid

English name: ascorbic acid

Molecular formula: C6H8O6

Known as: Vitamin C (vitamin C)

Definition: enolactone caprolactone. There are two isomers, L and D. Only the L form has physiological effects and is an important water-soluble vitamin.



Ascorbic acid is also a naturally occurring organic acid. It is found in humans, plants and microorganisms. Its molecular formula is C6H8O6. It is a white solid, but may sometimes appear yellowish. The yellowish colour represents the low purity level of ascorbic acid. Ascorbic acid has the above cyclic structure with an acidic group.


Ascorbic acid is soluble in water and other polar organic solvents. When dissolved in water, it forms a mildly acidic solution. When the loose proton from the hydroxyl group is bonded to the vinyl carbon, the molecule is stabilised by resonance stabilisation. This stability of the deprotonated conjugate base of ascorbic acid makes it more acidic than other hydroxyl groups. Ascorbic acid is an antioxidant like citric acid. As such, it reacts with oxidants of reactive oxygen species to produce harmful substances. For example, when ascorbic acid reacts with hydrogen peroxide, hydroxyl radicals are formed, which can damage vital molecules in cells. Ascorbic acid is a reducing agent. When exposed to air, it reduces oxygen to water. These reduction reactions are accelerated when light and metal ions are present. In the synthesis of ascorbic acid, glucose becomes the reactant. Most animals can synthesise ascorbic acid in the body. The conversion of glucose to ascorbic acid takes place in the liver, for which L-gulono-lactone oxidase is required. However, some animals, such as bats, primates, guinea pigs and birds, are unable to synthesise ascorbic acid because they lack this enzyme. This is also true for humans. So they should meet their ascorbic acid requirements from their diet.


L-Ascorbic acid

English name: L-Ascorbicacid

Molecular formula: C6H8O6

L-ascorbic acid, also known as vitamin C, is an essential nutrient for the human body. This is the form of ascorbic acid that animals and humans should ingest into their bodies if they cannot synthesise it. This is the l-enantiomer of ascorbic acid. The d-enantiomer has no important role in biological systems. As mentioned above, these are the compounds that act as reducing and antioxidant agents in biological systems. They are important for the synthesis of collagen, carnitine, neurotransmitters, tyrosine, etc. In addition, it is a cofactor in certain synthetic processes. Vitamin C deficiency can lead to the disease known as scurvy. The symptoms of this disease are brown spots on the skin, spongy gums and bleeding mucous membranes.


What is the difference between ascorbic acid and L-ascorbic acid?

*L-ascorbic acid is the L-enantiomer of ascorbic acid.

L-ascorbic acid is a more abundant compound in biological systems than d-ascorbic acid.

Some organisms can synthesize l-ascorbic acid in the body.



Preparation method and usage of L-Ascorbic acid

Preparation method

Glucose is hydrogenated and reduced to D-sorbitol under the catalysis of nickel, then fermented by oxidation with mycobacterium acetate at 30-34℃ and Ph value of 5.2-5.5 to produce L-sorbose. In the presence of fuming sulphuric acid and at -8℃, L-sorbose was condensed with acetone to diacetone sorbose; Catalyzed by nickel sulphate at 75-80℃, it was then oxidized with sodium hypochlorite to produce diacetone-2-keto-L-gulonic acid; finally, it was hydrolyzed under acidic conditions to produce 2-keto-L-gulonic acid; and then ascorbic acid was obtained.


Usage of L-Ascorbic acid

It is widely used as a nutritional supplement, antioxidant and colour protector for food.

1. L-Ascorbic acid can be used as a nutritional supplement and an antioxidant. Ascorbic acid is used as an antioxidant in many foods, including processed fruits, vegetables, meat, fish, dried fruits, soft drinks and beverages. It is added to pure fruit juices to maintain flavour over time and to fortify vitamin C. It is added to canned goods and syrups to prevent discolouration and flavour changes when canning peaches, apricots and cherries, and to beer and carbonated water to prevent oxidation and flavour deterioration. It can also be used as a wheat flour improver.


2. L-Ascorbic acid can be a reagent for the determination of arsenic, iron, iodine, bismuth, calcium, magnesium, titanium, tungsten, antimony and phosphorus. Reference substance for the determination of acid anhydride. Also it can used as a nutritional supplement and antioxidant.


3. L-Ascorbic acid can be used as an antioxidant and food fortification agent. It can be used in fermented pasta products at a maximum of 0.2g/kg,in beer, at a maximum of 0.04g/kg.


4. L-Ascorbic acid is involved in the complex metabolic processes of the body, promoting growth and increasing resistance to disease. It has strong reducing properties and can be used as an antioxidant. In the absence of L-Ascorbic acid or vitamin C, wounds or ulcers do not heal easily, bones and teeth are easily brittle and broken, while scurvy occurs: capillaries become more permeable, more brittle and easily ruptured and bleeding; in severe cases, muscles and internal organs bleed, leading to death. In China's regulations, vitamin C can be used in fortified sandwich hard candy with usage amount of 2000-6000mg/kg; in high iron cereals products (Daily consumption of 50g),800-1000mg/kg; in fortified baby food,300-500mg/kg; in fortified canned fruit,200-400mg/kg; in fortified drinks and milk beverages,120-240mg/kg; and in fortified fruit purees, 50-100mg/kg.


5. L-Ascorbic acid or vitamin C is involved in the complex metabolic processes of the body, promotes growth and enhances resistance to disease, increases egg production and improves eggshell quality in poultry. When animals are deficient in vitamin C, they will suffer from loss of appetite, growth stagnation, lack of fur matte and anaemia.


6. L-Ascorbic acid is used as an analytical reagent, e.g. as a reducing agent, masking agent, and used as a reagent for chromatographic analysis.


7. L-Ascorbic acid is used in cosmetics and food as an antioxidant to prevent pigmentation (age spots, freckles, chloasma). The dosage in cosmetics is 0.1% to 0.5% and in food 0.005% to 0.5%.


8. L-Ascorbic acid is used in galvanised iron alloy and nickel-iron alloy plating solutions, in chemical passivation solutions for precious metals and also for chemical analysis of solutions.


Physical and chemical properties of L-Ascorbic acid

Appearance and physical properties: white to very pale yellow crystalline powder Density: 1,65 g/cm3 Melting point: 190-194 °C (dec.) Boiling point: 415.8ºC at 760 mmHg Flash point: 180.4ºC Water solubility: 333 g/L (20 ºC) Refractive index: 21 °(C=10, H2O)

Chemical properties:

1. Relatively stable in dry air, but can be oxidized by air and light. Its aqueous solution is unstable, quickly oxidized to dehydroascorbic acid in neutral or alkaline solution and accelerate its oxidation in contact with light, heat, iron and copper and other metal ions to form stable metal salts. It is a relatively strong reducing agent and darkens to varying shades of pale yellow when stored for a long time. LC50 (mouse, intravenous): 518mg/kg.


2. Deteriorates easily when exposed to air and heat, oxidises easily and fails in alkaline solutions.


3. Present in the smoke and gas.


4. Widely exist in plants and animals. Stable to air in dry solid. Rapidly oxidised by air in aqueous solution.


Additional information.

1. Appearance: Usually in flakes, sometimes in acicular monoclinic crystals.