Glucose penta-acetate

P-Glucose penta-acetate. Grind together in a dry porcelain or glass mortar 4 g. of anhydrous sodium acetate (Section 11,50,d) and 5 g. of dry glucose and place the powdered mixture in a 200 ml. round-bottomed flask. Add 25 ml. of acetic anhydride, attach a reflux condenser and heat on a water bath until a clear solution is obtained (about 30 minutes shake the mixture from time to time). Continue the heating for a further 2 hours. Pour the reaction mixture into 250 ml. of ice-cold water in a beaker. Break up the solid lumps and allow to stand with occasional stirring for about 1 hour. Filter the crystals at the pump, wash well with water, and recrystallise from methylated spirit (or from methyl or ethyl alcohol) until the m.p. is 131-132° two recrystallisations are usually necessary. The yield is 7 g. 

Conversion of into ec-glucose penta-acetate. Add 0-5 g. of anhydrous zinc chloride rapidly to 25 ml. of acetic anhydride in a 200 ml. round-bottomed flask, attach a reflux condenser, and heat on a boiling water bath for 5-10 minutes to dissolve the solid. Then add 5 g. of the pure p-glucose penta-acetate, and heat on a water bath for 30 minutes. Pour the hot solution into 250 ml. of ice water, and stir vigorously in order to induce crystallisation of the oily drops. Filter the solid at the pump, weish with cold water, and recrystallise from methylated spirit or from methyl alcohol. Pure a-glucose penta-acetate, m.p. 110-111°, will be obtained. Confirm its identity by a mixed m.p. determination. 

Vigorous oxidation of a monosaccharide (e.j/., with dilute nitric acid) produces carboxyl groups at both ends of the chain. Thus galactose gives the sparingly soluble mucio acid glucose affords the soluble saccharic acid, which is bwi isolated as the sparingly soluble acid potassium salt. 

Disaccharides, t.g., lactose, which yield galactose upon hydrolysis, will also give the sparingly-soluble mucic acid but in poorer yield. This reaction may be employed for the differentiation between certain chsaccharides lactose — mucic + saccharic acids sucrose — saccharic acid only maltose — saccharic acid only. 

Dissolve 10 g. of lactose (1) in 100 ml. of nitric acid, sp. gr. 1 15, in an evaporating dish and evaporate in a fume cupboard xmtil the volume has been reduced to about 20 ml. The mixture becomes thick and pasty owing to the separation of mucic acid. When cold, dilute with 30 ml. of water, filter at the pump and set the filtrate (A) aside. Wash the crude acid with cold water. Purify the mucic acid by dissolving it in the minimum volume of dilute sodium hydroxide solution and reprecipitating with dilute hydrochloric acid do not allow the temperature to rise above 25°. Dry the purified acid (about 6 g.) and determine the m.p. Mucic acid melts with decomposition at 212-213°. 

COoH Saccharic acid 1 CHjOH Galactose 1 COjH Mucic acid 

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Acetates. Complete acetylation of all the hydroxyl groups is desirable in order to avoid mixtures. In some cases, the completely acetylated sugars may be obtained in the a- and p-forms depending upon the catalyst, e.g., zinc chloride or sodium acetate, that is employed in the acetylation. The experimental details for acetylation may be easily adapted from those already given for a- and p-glucose penta-acetates (Section 111,137). 

Conversion of /1-into a-D-glucose penta-acetate. Add 0.5 g of anhydrous zinc chloride rapidly to 25 ml of acetic anhydride in a 100-ml round-bottomed... 

Natunriss. 48, 304 (1961) Kraus, Pharmazie 19, 41 (1964). Synthesis from acetobromglucose and hydroquinone Man-nich, Arch. Pharm. 250, 547 (1912) from d-D-glucose penta-acetate + hydroquinone monobenzyl ether in the presence ol POClj Jarrett, U.S. pot. 3,201,385 (1965 to Polaroid). Frequently occurs together with methylarbutin in plants, particularly those of the family Ericaceae. 

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