Ascorbic Acid
Properties
| State | Solid at room temperature |
| Color | White to pale yellow crystalline powder |
| Solubility | Soluble in water (33 g/100 mL at 20 °C) |
| Melting Point | 190 °C (decomposes) |
About Ascorbic Acid
Ascorbic acid is the vitamin most humans get from food because we lost the ability to make it ourselves — about 60 million years ago, the primate lineage that includes humans, other apes, and guinea pigs accumulated an inactivating mutation in the L-gulonolactone oxidase gene that catalyzes the last step of vitamin C biosynthesis. Most other mammals still produce their own; we need a couple of pieces of citrus a day. Chemically, ascorbic acid is a five-membered lactone with a 2,3-enediol functionality that's responsible for both its biological role and its industrial usefulness. The enediol is easily oxidized to the diketone (dehydroascorbate), which is why ascorbic acid is such a strong reducing agent and why it works as an antioxidant in food preservation: it preferentially gets oxidized by ambient oxygen, sparing the food it's been added to. The pKa1 of 4.17 puts it in the realm of weak organic acids; the second proton (pKa2 = 11.6) doesn't typically come off under physiological conditions. In the body, ascorbic acid is the obligatory cofactor for prolyl hydroxylase and lysyl hydroxylase, the enzymes that hydroxylate proline and lysine residues in collagen — without those modifications, collagen triple helices don't form properly, and the resulting weak connective tissue produces the bleeding gums, loose teeth, and poor wound healing of scurvy.
Where you'll encounter it
If you take a vitamin C supplement, eat citrus fruit, or drink orange juice, the molecule doing the work is ascorbic acid. In a food-science context, it's the antioxidant added to commercial guacamole, pre-cut apple slices, and cured meats — the orange-red fading of cut apple flesh that ascorbic acid prevents is enzymatic browning catalyzed by polyphenol oxidase, and the ascorbic acid sacrificially reduces the oxidized phenolic intermediates back to colorless form. In a pharmacy, the standard cold-and-flu effervescent tablets are ascorbic acid plus sodium bicarbonate, which gives the fizzy CO2 release on dissolution. The historical context — James Lind's 1747 controlled trial showing that citrus cured scurvy in British sailors — is one of the earliest examples of a randomized clinical trial, predating the formal methodology by two centuries.
Common Uses
- Dietary supplement and antiscorbutic for vitamin C deficiency
- Food antioxidant preventing enzymatic browning (E300)
- Effervescent-tablet cold-and-flu pharmaceutical formulations
- Reducing agent in dough conditioners and cured-meat preservation
- Bench reductant for selective metal-ion redox chemistry
Safety Information
Very low toxicity — excess intake is excreted in urine within hours, and the practical upper limit before gastrointestinal upset (loose stools, mild cramping) is around 2 grams per day for most adults. Megadose use can rarely contribute to oxalate kidney stones in susceptible individuals, since one of the metabolic byproducts is oxalic acid. Generally safe at the doses found in food and standard supplements.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.