Vitamins C synthesis

Hexamethylphosphoramide Hoffmann, Roald, 1180 Hoffmann-I.a Roche Co., vitamin C synthesis and, 773 von Hofmann. August Wilhelm, 933 Hofmann elimination reaction. 936-938... 

Nickel oxide anodes are another example for a relatively simple oxide electrocatalyst used rather widely in the oxidation of organic substances (alcohols, amines, etc.) in alkaline solutions at relatively low anodic potentials (about +0.6 V RHE). These processes, which occur at an oxidized nickel surface, are rather highly selective. As an example, we mention the industrial oxidation of diacetone-L-sorbose to the corresponding acid in vitamin C synthesis. This reaction occurs at nickel oxide electrodes with chemical yields close to 100%. 

Table 4.9 Summary of reaction metrics and synthesis tree parameters for ascorbic acid (vitamin C) synthesis plans ranked according to overall kernel (maximum) RME .

The oxidation of carbohydrates at the nickel hydroxide electrode has been addressed in only a few papers [195]. Seiler and Robertson [197,198] developed a technical process, which allows the oxidation of 2,3,4,6-di-o-isopropylidene-L-sorbose (18, DAS) to protected gulonic acid (19). The acid, an intermediate of the vitamin C-synthesis, can be produced in a scale of two tons per day at the nickel hydroxide electrode. 

Early contributions to the oxidation of n-alcanols at nickel hydroxide electrodes have been described elsewhere More recent work is summarized in Table 1. Newer applications of the electrode, especially to the oxidation of 2,3 4,6-di-O-isopropylidene-L-sorbose (/) to L-gulonic acid (2), a step in a commercial vitamin C synthesis, were started by Vertes The development of the latter conversion to an industrial scale process was achieved by Robertson and Seiler . The mechanism... 

Alcohols can be converted electrochemically into the corresponding carboxylic acids in very good yields if Ni oxide anodes are used in alkaline electrolytes. This reaction was studied intensively in industry for the electrochemical oxidation of diacetone-L-sorbose to diacetone-2-ketogulonic acid (intermediates of the vitamin C synthesis). On the basis of Sowjet work 282 284) (initially Pt anodes and NaBr—NaCl—NiCl2— NaOH electrolytes subsequently Ni oxide anodes), Roche and Merck studied the synthesis on the laboratory and pilot scale. In cooperation with the ETH Zurich 285-286 a special cell 287 288) was developed for this reaction. 

Direct acetonation of L-sorbose is employed in the vitamin C synthesis. However, the diacetone-L-sorbose which is obtained is frequently contaminated by varying amounts of monoacetone-L-sorbose. The amount of monoacetone-L-sorbose87b in the diacetone derivative has been determined by petroleum ether extraction, followed by decomposition of the monoacetone derivative to acetone, which is determined iodimetrically. 

A nickel anode is in alkaline solution protected against corrosion by a layer of nickel oxides. oxide (NiOOH) is capable of oxidizing a number of functional groups primary alcohols may be oxidized to carboxylic acids [158-161], which is of interest for the technical production of an intermediate for vitamin C production [162]. NiOOH chemically oxidizes the substrate and is regenerated electrochemically a large anode surface, which is realized in the Swiss-roll cell (Chap. 31), is thus advantageous. NiOOH electrodes in form of nickel foam electrodes has been found to be useful for the oxidation of diacetone L-sorbose to diacetone 2-keto-L-gulonic acid in the vitamin C synthesis [163]. 

Some details are given by Merck in Ref. 112. The electrochemical oxidation is performed in alkaline solution using nickel or nickel oxide electrodes [113]. Hydrogen evolved at the cathode can be used for the hydrogenation of D-glucose to D-sorbitol, the first step in the vitamin C synthesis by the Reichstein route. Obviously, Merck doesn t use electrodes with high specific areas but prefers to stop the electrolysis at a conversion rate of 90%. The oxidation is completed with sodium hypochlorite solution. 

Examples are found for the selective hydroxylation, dehydrogenation and oxidative removal of side chains of steroids, and for the selective oxidation of sorbitol into L-sorbose in the vitamin C synthesis. 

Preparation. L-Sorbose is the most readily available l sugar, produced from D-glucitol as an intermediate in the vitamin C synthesis.153 Fermentations with Acetobacter suboxidans produce over 90% of L-sorbose. The ketose is obtained crystalline. In solution, the a-pyranoid tautomeric form is highly favored... 

Roche, Dairy the buildings used for vitamin C synthesis run from left to right at the top of the photograph (Urs Schachenmann, F. Hoffmann-La Roche AG, Basle)... 

Chatterjee, I. B., 1973b, Vitamin C synthesis in animals Evolutionary trend, Sci. Cult. 39 210-212. 

One study reported by Pal et al. (1975) indicated that lead toxicity impaired vitamin C synthesis in the rat. This finding is of no apparent significance to human nutrition because ascorbic acid is required in the human diet. Fox et al. (1980) have demonstrated that the addition of vitamin C to the diets of Japanese quail protected against high toxic levels of cadmium and decreased the concentration of cadmium in the liver and kidneys as compared to unsupplemented controls fed very low dietary levels of cadmium (Fox et al., 1970). Vitamin C increased the absorption of iron in the animal studies this increase probably was responsible for the observed protection against cadmium. 

Testicular hormone isolation Cholesterol structure Vitamin B2 isolation Vitamin C synthesis... 

Giovannoni, J. (2007) Completing a pathway to plant vitamin C synthesis. Proc. Natl. Acad. Sci. U.S.A. 104,9109-9110... 

Vitamin C—also called ascorbic acid, dehydroascorbic acid, hexuronic acid, and the antiscorbutic vitamin—is the very important substance, first found in citrus fruits, which prevents scurvy, one of the oldest scourges of mankind. All animal species appear to require vitamin C, but a dietary need is limited to humans, guinea pigs, monkeys, bats, certain fish, and perhaps certain reptiles. These species lack the enzyme L-gulonolactone oxidase which is necessary for vitamin C synthesis from 6-carbon sugars. 

K.D., and Ludwig, R. (2012) 2,5-Diketo-gluconic acid reductase from Corynebacterium glutamicum . characterization of stability, catalytic properties and inhibition mechanism for use in vitamin C synthesis. Process Biochem., 47, 2012-2019. 

Fioshin and coworkers also proposed the electrochemical synthesis of calcium gluconate [85] and diacetone-2-keto-L-gulonic acid (intermediate product in vitamin C synthesis [86, 87], see Sect. 9.2.7, Electrosynthesis of Diacetone-2-Keto-L-Gulonic Acid in the Vitamin C Production ). In collaboration with electrochemists in Khar kov (the group of Dr. Vasiliy Danilovich Bezuglyy, Sect. 9.1.6), they developed the technology for the production of salicylaldehyde [88]. M.Ya. Fioshin lectured applied electrochemistry to students, and a large number of specialists trained in his department continued to work in EKhOS. 

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