Preparation of Aldonic Acids

The above procedure was subject to various modifications. The bromine could be removed by aeration with air, carbon dioxide, hydrogen sulfide or sulfur dioxide. The hydrogen bromide formed in the reaction 

In most cases, after the hydrogen bromide had been removed, the resulting solutions were treated with various carbonates or with ammonium hydroxide to form the desired salts. The salts could be recrystallized directly from water or precipitated into ethanol. The choice of salt depended on circumstances thus, calcium D-gluconate crystallized well, but in the case of n-galactonic acid, the cadmium salt was preferable. The lead or cadmium salt was preferred when the free acid was desired since treatment of the aqueous solution or suspension with hydrogen sulfide easily removed the cation. The barium salts could be treated with the calculated amount of sulfuric acid and the calcium salts with oxalic acid for the same purpose. 

The formation of barium, calcium or lead salts has one other purpose, that of eliminating any dicarboxylic acids as water-insoluble salts. Herzfeld found that when zinc carbonate was used, the resulting zinc salts consisted of both n-gluconate and saccharate in the case of n-glucose both were soluble in water and insoluble in ethanol, whereas in the case of the barium salts, only the D-gluconate was soluble in water. 

Ruff reduced the amount of bromine in the preparation of larger amounts of the aldonic acids, so that one part of bromine was used with one part of sugar. A yield of 75 g. of calcium D-gluconate was obtained from 100 g. of D-glucose and 49.5 g. of cadmium D-galactonate from 100 g. of lactose. 

In a few cases the isolation of the free acid or lactone was carried out directly without the intermediate salt stage Fischer and Herborn isolated L-rhamnonic lactone by concentration of the aqueous solution after the bromide ions had been removed with lead carbonate, followed 

---

Derivatives of aldoses in which the terminal aldehyde function is oxidized to a car boxylic acid are called aldonic acids Aldonic acids are named by replacing the ose ending of the aldose by omc acid Oxidation of aldoses with bromine is the most com monly used method for the preparation of aldonic acids and involves the furanose or pyranose form of the carbohydrate... 

C. S. Hudson and H. S. Isbell, Relations between rotatory power and structure in the sugar group. XIX. Improvements in the preparation of aldonic acids, J. Am. Chem. Soc., 51 (1929) 2225-2229. 

Bromine (hypobromite) and hypoiodite oxidations are particularly useful for the preparation of aldonic acids from aldoses and of aldaric acids from glycuronic acids. Primary alcohol groups also undergo oxidation by these reagents, although this conversion is of less value glycosides can thus be converted into glycosiduronic acids, and alditols into aldoses and aldonic acids. 

L-arabinose and D-xylose in hemi-cellulose of sugar Cane, V, 279 Banana starch. See under Starch. Barium acid heparinate, III, 146 Barium 2-desoxy-D-gIuconate, III, 144 Barium D-gluconate, III, 144 Barium hypobromite, III, 163 Barium salts, in preparation of aldonic acids with NaCN, I, 23 Bark, tree, pentosan content, V, 271 Barley, alpha amylase of malted, V, 255-265... 

Calcium D-galactonate, I, 70 Calcium D-gluconate, III, 141, 142, 149, 152, 155, 156, 161 IV, 331 Calcium hypochlorite, III, 165 Calcium 2-keto-D-gIuconate, III, 148, 155 Calcium 5-keto-D-gluconate, III, 156 Calcium lactobionate, calcium bromide double salt, III, 155 Calcium Ievulinate, IV, 311 Calcium maltobionate, III, 161 Calcium D-mannonate, III, 152 Calcium pectate, I, 334 Calcium D-rhamnonate, III, 144 Calcium salts, in preparation of aldonic acids with NaCN, I, 23 Calcium vicianobionate, III, 154 Calcium D-xylonate, III, 155 Camphor, optically active, formed from inactive (racemic) camphor carboxylic acid in the presence of quinine, quinidine or nicotine, V, 53 Camphor carboxylic acid. See Camphor. Camphor, 3-hydroxy-, IV, 89 Camphorquinone, phytochemical reduction of, IV, 89... 

The field of halogen oxidation has developed primarily in two directions. The first is the preparation of aldonic acids by oxidation with bromine in acid solution. The second is the use of alkaline hypoiodite as a quantitative oxidant. Little work has been done on the mechanism of these reactions. The conditions under which the reactions are carried out have usually been established empirically without extensive study. The further use of solutions of known concentration and the comparison of various oxidants under similar conditions are to be desired. Critical oxidation potentials of various sugars used in relation to possible oxidants and ranges of pH might yield promising results. 

In the second place, oxidation by Fehling s or Tollens reagent cannot be used for the preparation of aldonic acids (monocarboxylic acids) from aldoses. Both Fehling s and Tollens reagents are alkaline reagents, and the treatment of sugars with alkali can cause extensive isomerization and even decomposition of the chain. Alkali exerts this effect, in part at least, by establishing an equilibrium between the monosaccharide and an enediol structure. 

Other articles " dealt with the preparation of aldonic acids, their lactones, and the basic calcium salts of aldonic acids obtained by electro-oxidation. By the procedure proposed, not only calcium, but also... 

Bromine and hypoiodite oxidations are particularly suitable for the preparation of aldonic acids from aldoses. Similarly, uronic acids are converted to saccharic acids. Of less value is the oxidation of primary alcoholic to aldehydic groups. In this manner, glycosides can be converted to uronides and polyols to aldoses and aldonic acids. 

Oxidation of aldoses with alkaline hypoiodite under carefully controlled conditions can lead to a stoichiometric yield of aldonic acids. This reaction has been used both as a measure of the amount of aldose present in a solution and for the preparation of aldonic acids. Determination of the iodine con-... 

---