2.3.4.6- Tetra-O-acetyl-D-gluconic acid

S-lactone (Note 1) is added slowly with vigorous stirring. During the addition, the temperature should be kept below 65°. After an hour in the ice bath, the solution is kept at room temperature for 24 hours and is then poured into 1 1. of water and stirred until the hydrolysis of the acetic anhydride is complete (about an hour). The mixture is placed in a refrigerator until the product crystallizes completely (Note 2). The crude material is removed by filtration and washed with a small amount of ice water. The 2,3,4,6-tetra-O-acetyl-D-gluconic acid monohydrate thus obtained melts at 113-117°. The yield is 79-84 g. (74-79%). 

Grushed fused ZnGlg shaken with acetic anhydride until almost dissolved, D-glucono-6-lactone added slowly with vigorous stirring and ice-cooling below 65 , after 1 hr. in the ice bath stored 24 hrs. at room temp., poured into water and stirred ca. 1 hr. 2,3,4,6-tetra-O-acetyl-D-gluconic acid monohydrate (Y ... 

Aldono-1,5-lactones and free aldonic acids react with alcohols in the presence of hydrogen chloride to give the corresponding alkyl aldonates (84). The reaction is slower with 1,4-lactones. Because esterification takes place very slowly in the absence of an acidic catalyst, aldonic acids and their lactones may be recrystallized from boiling alcohols without appreciable esterification (85). However, in some instances, alkyl esters are formed under these conditions. For example, essentially pure ethyl L-mannonate was isolated (6.4% yield) from the mother liquors of crystallization L-man-nono-1,4-lactone, obtained by Kiliani synthesis from L-arabinose (86). Similarly, repeated recrystallization from ethanol of crude 2,3,4,6-tetra-O-acetyl-D-glucono- 1,5-lactone afforded the corresponding ethyl gluconate derivative (87). 

Finally, methyl 2,3,4,6-tetra-0-acetyl-D-xfy(o-5-hexulosonate (84) has been reduced396 by hydrogenation in the presence of Raney nickel, to afford the corresponding derivatives of L-idonic and D-gluconic acid in the ratio of 9 1, from which the L-idonic acid derivative was isolated in 48% yield after acetylation. Interestingly, when reduced with sodium borohydride, 2,3,4,6-tetra-0-benzyl-lV,lV-di-methyl-D-xi//f)-5-hexulosonamide afforded the L isomer as the major component (no ratio given)459 as well. 

B. 2,3,4,5,6-Penta-O-acetyl-v-gluconic acid. Tetra-O-acetyl-D-gluconic acid monohydrate (50 g., 0.13 mole) is slowly added to a chilled (0-5°) solution of 18 g. of fused zinc chloride in 190 ml. of acetic anhydride contained in a 1-1. Erlenmeyer flask. The solution is kept in an ice bath for an hour and then allowed to stand at room temperature for 24 hours. After dilution with 1 1. of water, the solution is extracted with four 100-ml. portions of chloroform. In order to remove the chloroform, 200 ml. is distilled, 250 ml. of toluene is added, and 250 ml. of this solution is distilled. Another 250 ml. of toluene is then added and the volume is reduced to 300 ml. The product crystallizes on standing at 0° (Note 2). The solid is removed by filtration, washed with toluene and then with petroleum ether (b.p. 35-55°). A yield of 44-45 g. (83-84%) of anhydrous 2,3,4,5,6-penta-O-acetyl-D-gluconic acid, melting at 110-111°, is obtained [o ]d + 11.5° (c = 4.0 in ethanol-free chloroform). 

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