Regioselectively substituted cellulose esters and efficient methods of preparing them

Abstract

Embodiments of the invention provide regioselectively substituted carbohydrate and polysaccharide derivatives, such as cellulose esters, and methods for preparing them. Particular methods of the invention include deacylation of esters using tetrabutylammonium fluoride to obtain selective substitution at desired hydroxyl position(s) of the ester. Preferred is deacylation of an ester, which shows selectivity for removal of acyl groups from the ester of the secondary alcohols at C-2 and C-3, and which affords cellulose-6-O-esters with high regioselectivity by a simple one-step process employing no protective groups. Inventive regioselectively substituted cellulose esters can be prepared by such methods to obtain esters with the following anhydroglucose repeating units:

• • wherein R¹, R², and R³ are each independently chosen from a hydrogen atom, and, whether substituted or unsubstituted, branched or unbranched, an alkanoyl group, an aroyl group, and a heteroaroyl group. In embodiments, the alkanoyl, aroyl and heteroaroyl groups can comprise from 1-20 carbon atoms.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application relies on the disclosure of and claims priority to and the benefit of the filing date of U.S. Provisional Application No. 61 / 550,952, filed Oct. 25, 2011, the disclosure of which is hereby incorporated by reference herein in its entirety.BACKGROUND OF FR INVENTION[0002]1. Field of the Invention[0003]The present invention relates to the field of chemistry. More particularly, embodiments of the invention provide regioselectively substituted carbohydrate and polysaccharide derivatives, such as cellulose esters, and methods for preparing them.[0004]2. Description of Related Art[0005]Cellulose is one of the most abundant natural polymers on earth, consisting of unsubstituted, unbranched β(1→4) linked D-glucose units:Cellulose[0006]Cellulose comprises several thousand glucose units linked in a linear fashion. The chains are stabilized by intramolecular and intermolecular hydrogen bonds (shown as the dashed lines in the structur...

AI Technical Summary

Benefits of technology

[0016]Embodiments of the invention provide simple methods for achieving high regioselectivity in cellulose ester syntheses. Benefits of the invention include that the methods are simplified through the use of common organi

Problems solved by technology

The ability to prepare cellulose esters having a high degree of control over the position of substitution is, however, a very difficult problem in organic chemistry, polymer science, analytical chemistry, and materials science.

The paucity of general solutions to this problem is a limiting factor in the development of novel materials from renewable cellulose, which are an important part of a biorefinery-based economy.

In light of the low reactivity of cellulosic hydroxyl groups resulting from the hydrogen and, hydrophobic bonding, poor solubility, and steric hindrance, it is quite challenging to synthesize regioselectively substituted cellulose esters.

The relatively small reactivity differences between the 2-, 3-, and 6-OH groups, however, make selectivity very difficult to achieve, especially for esterification reactions, in which direct esterification of cellulose with sterically demanding acylating reagents provided only modest selectivity on 6-OH.

It is believed that the difficulty of regioselective substitution arises because of the low reactivity of cellulosi

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