Bromination of Cellulose with Tribromoimidazole and Triphenylphosphine under Heterogeneous Conditions.

Abstract

Bromination of bead cellulose was studied under heterogeneous conditions with tribromoimidazole and triphenylphosphine in several organic solvents. The addition of imidazole to the reaction system raised the degree of substitution with bromine (DSBr) of the products. The DSB, value increased at higher molar ratios of reagents to the repeating unit of cellulose and at longer reaction times, and exceeded 0.6 under appropriate conditions in dimethylacetamide or toluene-acetonitrile (1:2 v/v). The bromine distribution in the bromodeoxycellulose samples obtained was not homogeneous and 3,6-dibromo-3,6-dideoxyallose and 3,6-dibromo-3,6-dideoxyglucose units were contained even in the samples with DSB, lower than 0.5 along with 6-bromo-6-deoxyglucose and unmodified glucose units.

Deoxycelluloses and related structures

“…Here, LiBr/ DMAc works as a cellulose solvent for the homogeneous preparation and as a swelling agent for the heterogeneous reaction system. However, similar decreases in the intrinsic viscosity of the bromodeoxycellulose were observed comparable to those achieved with the triphenylphosphine/N-bromosuccinimide method [22,23]. As observed with the chlorodeoxycelluloses, bromination occurs first at the 6-position, and then at the 3-position in derivatives with a higher DS.…”