Chemistry of ascorbic acid Haworth and Szent-Györgyi, respectively. Ascorbic acid is a vinylogous carboxylic acid and forms the ascorbate anion when deprotonated on one of the hydroxyls. This property is characteristic of reductones: enediols with a carbonyl group adjacent to the enediol group, namely with the group –C(OH)=C(OH)–C(=O)–. The ascorbate anion is stabilized by electron delocalization that results from resonance between two forms: For this reason, ascorbic acid is much more acidic than would be expected if the compound contained only isolated hydroxyl groups. The ascorbate anion forms salts, such as sodium ascorbate, calcium ascorbate, and potassium ascorbate. Ascorbic acid can also react with
Chemistry of ascorbic acid the presence of free metal ions can not only promote but also initiate free radical reactions, thus making it a potentially dangerous pro-oxidative compound in certain metabolic contexts. Ascorbic acid and its sodium, potassium, and calcium salts are commonly used as antioxidant food additives. These compounds are water-soluble and, thus, cannot protect fats from oxidation: For this purpose, the fat-soluble esters of ascorbic acid with long-chain fatty acids (ascorbyl palmitate or ascorbyl stearate) can be used as food antioxidants. It creates volatile compounds when mixed with glucose and amino acids in 90 °C. It is a cofactor in tyrosine oxidation.