ON CARBOHYDRATES
Acylysis reactions are widely used in organic chemistry to cleave carbon–heteroatom - especially carbon–oxygen - bonds. The original procedure, applying acetic acid anhydride/anhydrous sulphuric acid, was already described by A. P. N. Franchimont in 1879 in his work about the treatment of cellulose (paper) to result in acetylated cellulose oligomers1. A major drawback of this type of reaction is its aggressiveness, causing browning reactions especially when applied on carbohydrates.
The new acylysis system pivalic acid anhydride/boron trifluoride etherate in dichloromethane at 40 oC cleaves cellulose triacetate without any detectable browning and with that, any side reactions2. Stopping the acylysis process at an appropriate time allows one to isolate and separate the most valuable short-chain oligomers of cellulose (as esters), at present up to the tetradecamer in sometimes astonishing high yields. Comparable results can be achieved with amylose triacetate.
A general discussion of mechanistic aspects of acylysis reactions exemplified by the description and results of key reactions, supported by high-level theoretical calculations, will lead to new insights on acylysis reactions.
1. A. P. N. Franchimont, Ber. Dtsch. Chem. Ges.,1879, 12, 1938-1942
2. P. Arndt, K. Bockholt, R. Gerdes, S. Huschens, J. Pyplo, H. Redlich, K. Samm, Cellulose 2003, 10, 75-83