Ascorbic acid, synthesis

Reichsteia and Grbssner s second L-ascorbic acid synthesis became the basis for the iadustrial vitamin C production. Many chemical and technical modifications have improved the efficiency of each step, enabling this multistep synthesis to remain the principal, most economical process up to the present (ca 1997) (46). L-Ascorbic acid is produced ia large, iategrated, automated faciUties, involving both continuous and batch operations. The process steps are outlined ia Figure 7. Procedures require ca 1.7-kg L-sorbose/kg of L-ascorbic acid with ca 66% overall yield ia 1977 (55). Siace 1977, further continuous improvement of each vitamin C production step has taken place. Today s overall ascorbic acid yield from L-sorbose is ca 75%. In the mid-1930s, the overall yield from L-sorbose was ca 30%. 

China. See also People s Republic of China acrylic fiber production in, 11.T89, 220 adhesive joint ventures, 1 526 advanced materials research, 1 696 aquaculture history, 3 183 aquaculture production, 3 189t ascorbic acid synthesis in, 25 754 demand for oil in, 23 530 nanocomposite development, 1 717 natural graphite in, 12 780 oil recovery program in, 23 534 olefin fiber production in, 11 243 production and consumption of regenerated cellulose fibers in,... 

Studies have been made on the individual steps in this synthesis. Acetonation104 of L-sorbose was studied with respect to time, temperature and the presence of metal catalysts, among which aluminum and zinc were found beneficial. Solvent extraction105 was discovered as a means of separating the monoacetone derivative from the desired diacetone-L-sorbose (see page 117). Reichstein and Griissner103 condensed L-sorbose with formaldehyde, with 2-butanone and with benzaldehyde but they found the diacetone derivative to be the most satisfactory intermediate in their ascorbic acid synthesis. A crystalline dicyclohexylidene derivative has also been proposed in this connection.100... 

Loewus, F.A., Kelly, S., and Hiatt, H.H., 1960. Ascorbic acid synthesis from D-glucose-2-14C in the liver of the intact rat. J. Biol. Chem. 235 937-939. 

A second synthesis in which a Ci fragment was coupled with a C5 fragment was reported in which acid chloride (8) was converted to the acyl nitrile (9) by use of silver cyanide (23) (Scheme 6). Hydrolysis and esterification produced ethyl 3,4,5,6-tetra-0-acetyl-DL-xyio-2-hexulo-sonate. The conditions required for the conversion of this material to DL-ascorbic acid will be discussed later. No yields were reported for this reaction sequence. This synthesis has not been used for the preparation of analogues or radiolabeled derivatives of L-ascorbic acid as has the osone-cyanide synthesis first reported (9-12). In contrast to the osone-cyanide synthesis (Scheme 5) in which a 3-ketogulonic acid derivative is produced, the acid chloride-silver cyanide synthesis (Scheme 6) results in the formation of a 2-ketogulonic acid derivative (2a) as an intermediate in the ascorbic acid synthesis. 

D-threo-2,5-Hexodiulosonic acid (40) is a pivotal intermediate in this ascorbic acid synthesis because the oxidation of glucose at Cl and C2 has already been accomplished and the inversion of stereochemistry... 

Sunlight is not necessary for the synthesis of ascorbic acid in plants but is needed to produce optimal vitamin C concentrations. Photosynthesis produces the precursor hexoses needed for ascorbic acid synthesis (38,51),... 

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