Cellulose, acetylation acid hydrolysis

By-product acetic acid is obtained chiefly from partial hydrolysis of cellulose acetate [9004-35-7]. Lesser amounts are obtained through the reaction of acetic anhydride and cellulose. Acetylation of saHcyHc acid [69-72-7] produces one mole of acetic acid per mole of product and the oxidation of allyl alcohol using peracetic acid to yield glycerol furnishes by-product acid, but the net yield is low. 

The basic cellulose unit contains three hydroxyl groups. The triester cellulose triacetate forms when cellulose is reacted with glacial acetic acid. Hydrolysis removes some of the acetate groups to form a secondary ester, which averages about 2.4 acetyl groups per unit rather than three. The secondary ester is then dissolved in acetone and the solution ejected through a spinneret to form fibers. Cellulose acetate processed in this manner is referred to as acetate rayon, but it may be more commonly known by its trade name Celanese. 

Sulfuric acid is a powerful esterification catalyst. It has been widely applied with mixtures of acetic acid and acetic anhydride to promote acetylations of numerous substances. Use of this catalyzed reaction for starch acetylation, however, has not risen to pre-eminence among starch acetylation methods as it has done among cellulose acetylations, although both reactions were discovered at the same time. The underdevelopment of this reaction in the starch field may be due to the following causes (1) sulfuric acid, a powerful acetylation catalyst, strongly catalyzes the hydrolysis of starch molecules and cannot be used for starch acetylations in the concentrations found most effective for cellulose reactions (2) most investigations of this reaction have been made on whole granules... 

The solubility restrictions that apply to the manufacture of the mixed esters are the same as those for the cellulose acetate, in that no soluble products are obtained by partial esterification. Hydrolysis of the esters in acid solution, however, yields uniform products showing gradually changing physical properties with increasing free hydroxyl content. The exact ratio of hydrolysis of acetyl to hydrolysis of propionyl or butyryl groups depends upon the composition of the hydrolysis solution. Thus, a cellulose acetate propionate hydrolyzed in acetic acid solution will retain a higher proportion of acetyl groups than would the same cellulose ester hydrolyzed in propionic acid. 

The anhydride method of acetylation gives an acid by-product that results in an acidic condition in the wood and a loss of 50% of the reaction chemical. These by-products must be removed to prevent degradation. Acetic acid, the by-product of acetylation with acetic anhydride, is virtually impossible to remove completely from wood. This results in a product that smells of acetic acid, acid conditions that catalyze the removal of more acetyl groups, acid hydrolysis of cellulose fibers which results in strength losses over a long term, and acid corrosion of metal fasteners used in the wood product. 

When cellulose (cotton fibers) is treated for several days with sulfuric acid and acetic anhydride, a combination of acetylation and hydrolysis takes place there is obtained the octaacetate of (-i-)-cellobiose. Alkaline hydrolysis of the octaacetate yields (-l-)-cellobiose itself. 

The formation of the A-oxide was avoided when trifluoroperacetic acid was reacted with the trifluoroacetate of acetyltropenol (67a, b). Recently it has been shown that hydrogen peroxide in formic acid gave a still better yield of epoxides without detectable A-oxides (67b). Acetylscopine (LXV) has been isolated as the picrate, (m.p. 212°) (67a), identical with the sample obtained from scopine (XLa) (75) hydrochloride by acetyl chloride (67a). The conversion of acetylscopine into ( ) scopolamine (LXV->XLb) has been realized (67b). Hydrolysis with A NaOH in acetone led to scopine (XLa), the hydrochloride of which was acylated, in turn, with acetyltropoyl chloride in nitrobenzene to acetylscopolamine besides a number of by-products. Separation was achieved using cellulose powder chromatography in butanol-A HCl. Acid hydrolysis of this ester with 2A HCl led to ( ) scopolamine hydrochloride (XLb) (67b) identical with the natural... 

Quantitative acid hydrolysis with 72% (w/w) H2SO4 [19] was used to characterize the BSG feedstock. The monosaccharides and acetic acid were determined by HPLC to estimate (after corrections for stoichiometry and sugar decomposition) the contents of glucan (cellulose) and hemicelluloses (xylan, arabinan, and acetyl groups) in the sample. The acid-insoluble residue after hydrolysis was recovered by filtration and considered as Klason lignin after correction for the acid-insoluble ash. Protein was determined by the KJeldahl method [20] using the Ax 6.25 conversion factor. 

Cellulose triacetate is often known as primary cellulose acetate, and partially hydrolyzed material is called secondary cellulose acetate. Many physical and chemical properties of cellulose acetylation products are strongly dependent on the degree of esterification, which is measured by the acetyl content (i.e., the weight of acetyl radical (CH3CO-) in the material) or acetic acid yield (i.e., the weight of acetic acid produced by complete hydrolysis of the ester). 

Cellulose is a carbohydrate, the structure of which may be deduced as follows. The molecular formula of cellulose is (C6HioOs)n, where n is a few thousand (see later). Hydrolysis of cellulose by boiling with concentrated hydrochloric acid yields D-glucose (II) in 95-96% yield. Thus cellulose is a polyanhydroglucose. When cellulose is subjected to acetolysis (i.e., simultaneous acetylation and hydrolysis) by treatment with a mixture of acetic anhydride and concentrated sulphuric acid, cellobiose octa-acetate is formed. Thus the structure of cellulose is based on the cellobiose unit. Cellobiose is known to be the disaccharide, 4-0-j3-D-glucopyranosyl-D-glucopyranose (III). Finally, very careful acetolysis of cellulose produces a cellotriose, a ceUotetraose and a cellopentaose and in each of these all the 1,4-links have been shown to be j3-links (from calculations of the... 

---