Org. Synth. 1942, 22, 53
DOI: 10.15227/orgsyn.022.0053
β-GENTIOBIOSE OCTAACETATE
[Gentiobiose, β-octaacetyl-]
Submitted by B. Helferich and J. F. Leete.
Checked by Homer Adkins and E. E. Bowden.
1. Procedure
A solution of 1.65 kg. of crystallized glucose or 1.5 kg. of anhydrous glucose (8.3 moles) is prepared by heating the solid on a steam bath with 1.35 l. of distilled water. The solution is cooled and placed in a 2.5-1. glass-stoppered bottle. Fifteen grams of emulsin (Note 1) is added, then 20 ml. of toluene, and the flask is closed and allowed to stand at room temperature, with occasional shaking, for 5 weeks. The solution is then boiled, diluted with 8.5 l. of water, and filtered. To the filtrate is added 56 g. of baker's yeast in 650 ml. of water, and the temperature of the mixture is maintained at 28–32° for 12–14 days (Note 2). The mixture is then boiled for 30 minutes with an excess of powdered calcium carbonate and filtered.
The filtrate is evaporated under a pressure of 20–30 mm. to as thick a syrup as possible. For this operation the solution is placed in a 12-l. flask set in a steam bath and connected by a goose-neck to a condenser, which in turn is connected to a suction or distilling flask. A very fine capillary inlet tube into the 12-l. flask prevents any violent ebullition (Note 3) and (Note 4).
To the thick syrup (170–185 g.) are added 100 g. of anhydrous sodium acetate and 1.125 l. of acetic anhydride. The mixture is carefully heated to the boiling point with provision for cooling the flask with wet cloths should the acetylation become too violent. When the reaction is complete (about 20 minutes is required) the solution is poured into 10 l. of ice water. The water is decanted and renewed twice at 24-hour intervals in order to render the acetylated sugar filterable.
The dark brown product is filtered and, after drying in the air, is extracted with ether in a Soxhlet apparatus. The ether is removed by evaporation, and the light-colored residue (170 g.) is recrystallized from 1.65 l. of hot methanol. The crystals are washed on a Büchner funnel with methanol until free from colored impurities. The yield is 77–87 g. of material which melts at 187–190°. A second recrystallization from methanol (1.25 ml. per g. of product) gives pure βoctaacetylgentiobiose, with about 10% loss. The pure substance melts at 196° (cor.).
2. Notes
1.
A commercial sample of emulsin was purchased from Merck and Company. If freshly prepared emulsin of good quality is available, the quantity may be reduced to one-tenth or less of the specified amount.
2.
The yeast, by fermentation, removes the
glucose which has not been transformed into
gentiobiose. Fleischmann's and "Red Star" yeast have been used. The flask should be stoppered and protected with the conventional trap for the escape of
carbon dioxide.
3.
The submitters suggest a more complicated apparatus
(Note 4) for this operation. However, the checkers have had no trouble with foaming or bumping when using the simple apparatus described above. Very little water condenses in the receiver, which serves as a safety trap in case foaming or bumping should occur.
4.
The submitters used quantities four times as large as those stated above. They give the following directions for the distillation:
"The solution is drawn slowly through a glass tube provided with a stopcock into a 3-l. distillation flask standing in a bath of rapidly boiling water. The small portion which foams over is collected and evaporated in a second 3-l. distillation flask, likewise standing in rapidly boiling water. The distillate is passed through an efficient condenser and is collected in a thick-walled bottle or flask to which the vacuum pump or water pump is connected. A high vacuum is essential. The tube connecting the condenser and the receiver is provided with a stopcock so that the distillate may be poured out without interrupting the vacuum to any extent."
3. Discussion
The chief methods for the preparation of
gentiobiose and its octa-acetate are discussed in a paper by Reynolds and Evans.
1,2 These methods involve isolation of the substance from gentian root;
3,4 the action of emulsin on
glucose;
5,6 the catalytic hydrogenolysis of
amygdalin;
7 separation from the mother liquors ("Hydrol") obtained in the manufacture of
glucose;
8 and the condensation of
acetobromoglucose with
β-d-glucose-1,2,3,4-tetraacetate.
1,9,10 Reynolds and Evans recommend the last-mentioned method.
The method given above is a modification of those originally described by Bourguelot
3 and Zemplén.
11This preparation is referenced from:
Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)
amygdalin
Gentiobiose, β-octaacetyl-
gentiobiose and its octa-acetate
methanol (67-56-1)
ether (60-29-7)
acetic anhydride (108-24-7)
sodium acetate (127-09-3)
carbon dioxide (124-38-9)
calcium carbonate (471-34-1)
toluene (108-88-3)
glucose (492-62-6)
Acetobromoglucose (572-09-8)
β-Gentiobiose octaacetate (4613-78-9)
Gentiobiose (554-91-6)
β-D-Glucose-1,2,3,4-tetraacetate (13100-46-4)
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