Synthesis of L-Ascorbic Acid

Abstract

This chapter provides a summary of the methods developed for the synthesis of L-ascorbic acid. L-Ascorbic acid is a white, crystalline solid melting at 192°C and having, in water, a specific rotation at the sodium D line of +24°. In solution, L-ascorbic acid has a pK1 of 4.17 and a pK2 of 11.79. The more-acidic proton has been shown by both chemical and physical methods to be that of the 3-hydroxyl group. The structure of L-ascorbic acid in solution has been studied by C-NMR spectroscopy, suggesting that a variety of tautomeric structures is possible. L-Ascorbic acid has also been synthesized from D-galacturonic acid —a hexose derivative not as readily available as D-glucose. In the chapter, the methods of preparation of precursors in the various syntheses are discussed. Many of the methods used for the preparation of analogs are based on the procedures used for the synthesis of L-ascorbic acid. The synthesis and biological activity of a number of these analogs are reviewed in the chapter.