Polysaccharides mixed esters

Although most polysaccharides may be acylated without degradation, acyl derivatives of xylans29 are often unsatisfactory for molecular-weight determinations owing to their poor solubility characteristics. Mixed esters of xylans143 are often superior in this respect, but there are obvious difficulties in the differential analysis of acyl groups. Hemicellulose nitrates have been used for measurements of molecular size,168 but xylan nitrates,29 like xylan acetates, are reported to have poor solubility characteristics. 

It is possible to react almost any acid with a polysaccharide to produce an ester, and a great variety of polysaccharide esters have been produced. Polysaccharide esters of aliphatic acids are readily prepared by reacting the free acid with the polysaccharide in the presence of an impelling agent consisting of a mixture of chloroacetic anhydride, chloroacetic acid, and magnesium perchlorate Mixed esters, especially the acetate-propio-... 

More recent developments in the field of the Pirkle-type CSPs are the mixed r-donor/ r-acceptor phases such as the Whelk-Of and the Whelk-02 phases.The Whelk-Of is useful for the separation of underiva-tized enantiomers from a number of families, including amides, epoxides, esters, ureas, carbamates, ethers, aziridines, phosphonates, aldehydes, ketones, carboxylic acids, alcohols and non-steroidal anti-inflammatory drugs.It has been used for the separation of warfarin, aryl-amides,aryl-epoxides and aryl-sulphoxides. The phase has broader applicability than the original Pirkle phases. The broad versatility observed on this phase compares with the polysaccharide-derived CSPs... 

Another potentially important fermentation is that producing butyric acid. The process is used industrially on only a small scale at present and details have not been disclosed. Many derivatives of butyric acid are used industrially the benzyl, methyl, octyl and terpenyl esters are used in the perfumery and essence trade and amyl butyrate, bornyl and isobornyl butyrates have been described as plasticizers for cellulose esters. Moreover vinyl butyrate is a possible ingredient of polymerizable materials. The mixed acetic and butyric acid esters of polysaccharides are also coming into favor. Cellulose acetate butyrate is marketed as an ingredient of lacquer and is less inflammable than the pure acetate. Dextran (see below) acetate butyrate may have similar uses. 

CMD and mixed derivatives based on CMD may be used for the fixation of antibiotics and enzymes on a polysaccharide matrix. A procedure was developed for amidation of CMD and its ethyl ester (CMDEE) with various aromatic amines in dioxane (100 °C), ethanol (78 °C), n-propanol (97 °C) and 2-propanol (82 °C) in the presence of a small amount of water [301]. CMDEE reacts with aliphatic and aromatic amines but in the case of amino acids the degree of amidation depends on the position of the amino moieties in the acids [302,303]. The DS decreases from S-, y-, /3, to a-amino acids. For the reaction with a-amino acids, carboxymethyl and carboxyethyl dextran azides are used [304],... 

The present work summarizes the some results of these studies. The article describes some new types of cellulose etho and esters, a number of mixed polysaccharides based on cellulose, which have been synthesized by the authors and their coworkers, and also discusses the principles governing a number of reactions for effecting tte chemical transformatiem of cellulose, i.e. nucleophilic sutetitution, trtms-esterifica-tiem, ionic and free-radical additimi, which enable new types d cellulose derivatives to be synthesized. 

The chemical transformations that lead to the conversion of cellulose to mixed polysaccharides differing from cellulose in the conformation of the pyranose ring and the number and configuration of the hydroxyl groups of the repeating unit of the macromolecule, may exert a considerable effect on the structure of the material as well as on its important chemical properties (rate of acetylation and O-alkylation of OH groups, stability of the acetal linkage) and physicochemical indices (solubility of modified preparations of cellulose and cellulose ethers and esters). 

It should be noted that it is not only preparations of mixed polysaccharides which differ from cellulose in solubility, but also esters (acetates, nitrates) do not dissolve com Jetely m solvents of the corresponding cellulose esters. Thus, the nitrate of mixed polysaccharide(III), which contains 42 mol.-% of altrose, dissolves in acetone to 68%, and the triacetate dissolves in methylene chloride to 65 %. 

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