*3.1.1 Acidity of a substance*

Due to the possibility of the two hydroxyls of the five-membered lactone ring dissociating because of the close proximity of a double bond, ascorbic acid functions as a diprotic acid (enolic hydroxyls). Although the second dissociation is incredibly weak (pK2 = 11.57), the initial dissociation is fluent (pK1 = 4.17, or almost four times stronger than acetic acid). When titrated with solutions of strong bases, ascorbic acid behaves as a monoprotic acid in aqueous solutions and produces a single equivalency point.

It should be mentioned that ascorbic acid was classified as a monoprotic acid during the initial experiments that were conducted. Only extremely, alkaline solutions contain the discharged anion because ascorbic acid is now unstable (lactone ring opening + cleavage) and its solutions quickly oxidize in the presence of oxygen from the atmosphere. Delocalization of the electrons of the carbonyl double bond and coordination of its two normal forms stabilize the singly charged ascorbate anion. This explains why ascorbic acid has a high acidity and what causes it to be "reluctant" to experience the second dimension.

## *3.1.2 Reducing capacity*

A mild to moderately potent reducing agent is ascorbic acid. It is substantially more powerful than straightforward reducing sugars because it contains the exceptionally active and rather uncommon enediol group, C(OH) = C(OH)-. Mild oxidizing agents convert it to dehydroascorbic acid as a result. Its total chemical reversibility is what makes this reaction unique. Dehydroascorbic acid is quantitatively reduced to ascorbic acid by reducing agents such as HI, H2S, and thiols. In the body, glutathione and other thiol substances directly diminish it.

Dehydroascorbic acid preserves the biochemical features of vitamin C, with the exception of course of its antioxidant capacity, thanks to the reversible redox system of ascorbic/dehydroascorbic acid's active participation in a number of biochemical coupled redox processes.

*Ascorbic Acid in Sepsis and Septic Shock DOI: http://dx.doi.org/10.5772/intechopen.109515*

It is distinctive that ascorbic acid, unlike dehydroascorbic acid, cannot enter the brain through the bloodstream.

As a result, the metabolic reduction of dehydroascorbic acid there yields the ascorbic acid that is found in the brain (and in fact in higher amounts compared to other organs of the body). Dehydroascorbic acid can enter cells through the glucose transporter, but ascorbic acid often cannot. In aqueous solutions, ascorbic acid is easily oxidized by oxygen in the air. This reaction is aided by small concentrations of different metal ions, primarily Cu2+, and is more favored in neutral and alkaline solutions. The interaction between acidic liquids and ambient oxygen happens rather slowly.

The following are examples of ascorbic acid oxidation processes [18]:

2C6H8O6 O2 2C6H6O6 2H2O + +

C6H8O6 2Fe3 2C6H6O6 2Fe2 2H + + + ++ +

$$\text{C}6\text{H}8\text{O}\text{€} + \text{I}2\text{C}\text{C}\text{H}\text{€}\text{O}\text{€} + 2\text{I} - + 2\text{H} + \tag{1}$$
