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Org. Synth. 1937, 17, 36
DOI: 10.15227/orgsyn.017.0036
α-CELLOBIOSE OCTAACETATE
Submitted by Géza Braun
Checked by Reynold C. Fuson, William E. Ross, and William P. Campbell.
1. Procedure
In a 1-l. wide-mouthed bottle with a glass stopper, 400 cc. of acetic anhydride is cooled to −10° in a freezing mixture and 36 cc. of concentrated sulfuric acid is added at once with constant stirring. The temperature of the solution rises to about 20°. The bottle is removed from the freezing mixture, and 20 g. of absorbent cotton (Note 1) is worked into the liquor immediately with a heavy glass rod. With constant stirring, the bottle is warmed in a water bath maintained at 60° until the temperature of the mixture reaches 45° (about ten minutes), and then it is removed and the temperature is kept from rising above 55° by suitable cooling with running water, stirring being continued throughout (Note 2). After about twenty minutes (total) the mixture becomes thin; at this point it is cooled to 50° and a second 20-g. portion of cotton is added with stirring, the temperature again being kept from rising above 55°. The process of cooling to 50° and adding 20 g. of cotton is repeated at intervals of about ten minutes until 100 g. of cotton in all has been introduced. After the final addition stirring is continued until the mixture becomes thin (about ten minutes); then the bottle is stoppered and heated in a bath maintained at 50° for one hour, during which time the cotton dissolves completely to a thin, light brown syrup. The stoppered container is kept in an oven at 35° for seven days.
The solution darkens to a deep wine-red color, and α-cellobiose octaacetate begins to crystallize on the second day (Note 3). After seven days at 35° the semi-crystalline mass is stirred into 0 l. of cold water. With good stirring the flocculent precipitate of α-cellobiose octaacetate and cellulose-dextrin acetates soon becomes crystalline; after standing for one to two hours the solid is collected on a 12.5-cm. Büchner funnel, washed free from acid with cold water, and drained thoroughly. The moist product, weighing about 250 g., is triturated with 250 cc. of warm methyl alcohol, and, after cooling to room temperature, the undissolved solid is collected on a 7-cm. Büchner funnel, washed with three 50-cc. portions of methyl alcohol, and dried at 40°. The yield of fairly pure α-cellobiose octaacetate is 69–74 g. For purification it is dissolved in 300 cc. of chloroform and the solution is filtered by suction into a dry receiver through a pad prepared by dusting Norite onto a Büchner funnel and washing the funnel with alcohol. The chloroform solution is filtered while the pad is still wet with alcohol, and the filter is washed at once with 100 cc. of chloroform without interruption in the filtration. The colorless filtrate is concentrated at reduced pressure until the acetate begins to crystallize (about 250 cc.), the crystals are redissolved by warming, and the solution is poured into 750 cc. of warm methyl alcohol. The acetate begins to crystallize at once as small needles which eventually form a thick paste. The mixture is cooled to 0° with stirring, and after about one hour the material is collected, washed with 100 cc. of methyl alcohol, and dried at 40°. The yield of colorless α-cellobiose octaacetate, m.p. 220–222°, [α]20°D + 41.6°, is 65–69 g. (35–37 per cent of the theoretical amount, assuming that the cotton contains 10 per cent of moisture) (Note 4), (Note 5), and (Note 6).
For further purification a solution of the material in 350 cc. of chloroform is clarified if necessary and poured into 750 cc. of methyl alcohol, and the mixture is cooled to 0°. The yield of the pure acetate, m.p. 225–226°, [α]20°D + 42.5°, is 61–65 g. The constants are not altered by further crystallizations.
2. Notes
1. Pure commercial cotton or filter paper may be used. These materials ordinarily contain 7–10 per cent of moisture.
2. Effective stirring and careful control of the reaction are essential to obtain good yields. If left uncontrolled, the temperature may rise quickly above 100° with considerable decomposition.
3. The crystallization is accelerated by scratching the walls of the jar or by seeding. Seed is obtained easily by pouring a small portion of the reaction mixture into a large amount of water; the precipitate is separated, treated with alcohol, and dried at 40°.
4. In earlier experiments a temperature of 30–40° was maintained during the addition of the cotton (which then required more time), and the acetolysis was allowed to proceed at room temperature for six days. The yield of product melting at 220–222° was 50–56 g., but rose to 62–70 g. when the period of digestion was extended to eight days.
5. The quantities can be doubled without change in the procedure or the percentage yield.
6. Pringsheim's method1 of isolating the acetate gives equally good results. Instead of pouring the acetolysis mixture into water, it is kept at 0° for one to two days and the crystalline material is collected on a large Büchner funnel and washed with 50 cc. of ice-cold acetic anhydride. Cellulose-dextrin acetates and other by-products pass into the filtrate. The crude mass is digested with 200 cc. of warm methyl alcohol, collected, and crystallized from chloroform-alcohol as above. The yield is 65–68 g., m.p. 220–222°.
3. Discussion
The preparation of α-cellobiose octaacetate by the acetolysis of cellulose was discovered by Franchimont,2 and the process has been studied carefully by a number of other investigators.1, 3, 4, 5 The observations of Freudenberg4 and Klein5 were particularly useful in developing the present procedure.
This preparation is referenced from:

References and Notes
  1. Pringsheim and Merkatz, Z. physiol. Chem. 105, 173 (1919).
  2. Franchimont, Ber. 12, 1941 (1879).
  3. Skraup and König, Monatsh. 22, 1011 (1901); Maquenne and Goodwin, Bull. soc. chim. (3) 31, 854 (1904); Schliemann, Ann. 378, 366 (1911); Ost, ibid. 398, 332 (1913).
  4. Freudenberg, Ber. 54, 767 (1921).
  5. Klein, Z. angew. Chem. 25, 1409 (1912).

Appendix
Chemical Abstracts Nomenclature (Collective Index Number);
(Registry Number)

Cellulose-dextrin acetates

cellulose

sulfuric acid (7664-93-9)

methyl alcohol (67-56-1)

acetic anhydride (108-24-7)

chloroform (67-66-3)

Norite (7782-42-5)

chloroform-alcohol

α-Cellobiose octaacetate (5346-90-7)