L-Ascorbic Acid

Basic Concept

L-Ascorbic acid (CAS 50-81-7), commonly known as vitamin C, is a water-soluble vitamin and an organic compound with strong reducing activity. Its molecular formula is C6H8O6, its molecular weight is 176.12, and its EINECS number is 200-066-2. Humans cannot synthesize vitamin C and must obtain it from dietary or other external sources.

Ascorbic acid can be reversibly oxidized to dehydroascorbic acid in redox processes. This behavior underlies both its nutritional role and its technical use as an antioxidant, reducing agent, and formulation-stability aid.

Physical and Chemical Properties

• Appearance: White or slightly yellow crystalline solid or crystalline powder, generally odorless with an acidic taste.
• Solubility: Freely soluble in water, soluble in ethanol, and insoluble in ether, chloroform, benzene, oils, and fats.
• Melting point: Approximately 190-194 °C with decomposition.
• Density: Approximately 1.65 g/cm3.
• Acid-base behavior: Its aqueous solutions are acidic, with pKa values of approximately 4.04 and 11.7 at 25 °C; solution pH decreases as concentration increases.
• Optical rotation: Specific rotation is typically about +19° to +23° (c=10% in water).
• Structural behavior: The enediol group is readily oxidized and accounts for the compound's reducing activity.

Stability and Storage

The dry material is relatively stable, whereas aqueous solutions oxidize more readily, particularly under neutral or alkaline conditions. Light, heat, air, and metal ions such as copper and iron accelerate degradation. Contact with oxidizing agents and bases should be avoided. Store tightly closed in a cool, dry place protected from light, and prepare solutions shortly before use whenever practicable.

Physiological Roles

• Antioxidant and redox activity: Functions as a water-phase antioxidant and participates in physiological redox processes that support a normal cellular environment.
• Collagen formation: Acts as an important cofactor in hydroxylation reactions involved in collagen synthesis and therefore contributes to connective tissue, skin, blood-vessel, gum, and wound integrity.
• Iron utilization: Reduces ferric iron to the more readily absorbed ferrous form, supporting the absorption and utilization of non-heme iron.
• Metabolic support: Participates in folate and amino-acid metabolism and supports normal immune function.

Deficiency

Prolonged inadequate intake impairs normal collagen formation, and severe deficiency causes scurvy. Typical findings can include fatigue, swollen or bleeding gums, petechiae or bruising, increased capillary fragility, delayed wound healing, and anemia associated with reduced iron absorption. Severe deficiency in children may also interfere with normal bone and tooth development. This section provides general product and nutritional information and is not intended for diagnosis or treatment.

Principal Uses

• Food and beverages: Used as a nutrient fortifier, antioxidant, color-protection aid, and flour-treatment ingredient. Permitted applications and use levels depend on local food regulations.
• Pharmaceuticals and nutrition: Used in vitamin preparations, dietary supplements, and pharmaceutical formulations; pharmaceutical applications require a grade meeting the relevant pharmacopeial or registered specification.
• Animal feed: Used as a vitamin source and antioxidant component in appropriate animal-nutrition formulations.
• Cosmetics and personal care: Used for antioxidant, pH-adjusting, and skin-conditioning functions, with formulation and packaging selected to manage stability.
• Laboratory and industrial: Used as a reducing agent, antioxidant, masking agent, and analytical reagent in methods involving arsenic, iron, phosphorus, iodine, and other analytes.

Application Note

Food, pharmaceutical, feed, and reagent grades differ in quality standards, impurity limits, and regulatory status. Selection should be based on the applicable regulation, pharmacopeia, or industry standard, with the supplier's batch-specific COA and SDS used as the controlling documents.