Cellulose sulfate esters

Several anionic carbohydrate polymers (e.g., carboxymethyl cellulose, xanthomonas campestris polysaccharide, cellulose sulfate ester, etc.) do not adsorb from fresh water solutions, but their adsorption in saline solutions plays an... 

Cellulose sulfate esters with the proper D.S. values are water soluble and have applications such as food thickeners, textile sizes, viscosity modifiers for oil-drilling muds and in pharmaceutical applications. 

To a first approximation the exponential constant, a, in the Mark-Houwink equation reflects the solution conformation of a macromolecule. The exponential constants for the carbohydrate polymers studied, excluding the cellulose sulfate ester, are listed in Table I. Generally a value of 0.7-0.8 reflects a random coil conformation as the constant approaches or exceeds 1.0 the conformation approaches a rod-like shape. 

Cellulose sulfated usiag sulfamic acid degrades less than if sulfated usiag sulfuric acid (23). Cellulose esters of sulfamic acids are formed by the reaction of sulfamyl haHdes ia the presence of tertiary organic bases (see Cellulose esters). 

Ca.ta.lysts for Acetylation. Sulfuric acid is the preferred catalyst for esterifying cellulose and is the only known catalyst used commercially for this function. The role of sulfuric acid during acetylation has been discussed (77,78). In the presence of acetic anhydride, sulfuric acid rapidly and almost quantitatively forms the cellulose sulfate acid ester (77). Even in the absence of anhydride, the sulfuric acid is physically or mechanically retained (sorbed) on the cellulose. The degree of absorption is a measure of the reactivity or accessibiUty of different celluloses. 

Sulfuric acid reacts with acetic anhydride to form acetylsulfuric acid (79). This reaction is favored by low temperature and high anhydride concentration. In cellulose acetylation, probably both sulfuric acid and acetylsulfuric acid exist and react with cellulose to form cellulose sulfate acid ester. 

Hydrolysis. The primary functions of hydrolysis are to remove some of the acetyl groups from the cellulose triester and to reduce or remove the combined acid sulfate ester to improve the thermal stabiUty of the acetate. 

The ester is washed thoroughly in iron-free water to remove acid and any desirable salts these wash Hquids are sent for acid recovery. The final wash may contain some sodium, calcium, or magnesium ions to stabilize traces of sulfate esters remaining on the cellulose acetate. 

Cellulose Sulfates and Phosphates. Conversion of cellulose to sulfate or phosphate monoesters produces soluble derivatives. These ester groups are highly hydrated, offer steric interference to molecular fit, and are ionized at all PH levels so they continually produce coulombic repulsion. 

Because only one valence of sulfur is occupied for ester formation, the product is acid. Cellulose sulfates are water soluble and can be used as thickening agents. 

Partial hydrolysis is accomplished by adding to the methylene chloride solution aqueous acetic acid (50%). The solution is then allowed to stand in order to reach the desired degree of hydrolysis. This usually takes about 72 hours at room temperature. Sulfuric acid, still present from acetylation, is then neutralized by addition of sodium acetate and most of the methylene chloride is distilled off. The partially hydrolyzed cellulose acetate is then precipitated by addition of water and washed thoroughly. The washing also includes a two-hour wash with very dilute sulfunc acid to remove hydrogen sulfate esters that cause polymer instability. 

Thermally stable sulfate esters have been prepared by treating cellulose with mixtures of sulfuric acid and C, to alcohols in an inert diluent (e.g. toluene, carbon... 

Sulfate esters have also been prepared using preformed diafeylamide-sulfur trioxide (DMF.SO,) complexes. The reaction is heterogeneous but the complex can penetrate into the cellulose crystalline regions, producing highD.S. values) 2.0) and a very uniform distribution of the sulfate groups (31). 

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