Control of depolymerisation during the preparation of reduced dialdehyde cellulose

Abstract

The severe depolymerisation that occurs when cellulose is oxidised by periodate can be greatly diminished by carrying out the oxidation in steps, with borohydride reduction after each, and by using propan-1-ol as a radical scavenger in the oxidation steps. The reduction steps greatly increase the rate of Malapradian oxidation by eliminating hemiacetal structures and increasing the solubility of the substrate. They also minimise free-radical-mediated depolymerisation, and prevent the over-oxidation (stepwise peeling) that otherwise ensues at the newly liberated reducing end-groups. The use of regenerated cellulose or mercerised cellulose in order to increase accessibility is also advantageous. Depolymerisation by β-elimination in the reduction steps can be minimised by using very concentrated aqueous sodium borohydride. By these methods, a sample of fully oxidised and reduced cellulose with M n = 132,000 was prepared.