Propargylation of arabinogalactan with propargyl halides-a facile route to new functionalized biopolymers

摘要

New arabinogalactan propargyl ethers with degree of substitution (DS) up to 2.8 have been obtained by propargylation of arabino-3,6-galactan (AG) with propargyl bromide (PB) in the two-phase system 30- 60% ROH aqueous solution/toluene in the presence of triethylbenzylammonium chloride (TEBAC) or without catalyst (ambient temperature, 1-24 h) in 20-87% yields. The highest yields have been reached using TEBAC as phase-transfer catalyst, though the non-catalytic version proves to be also efficient (DS 2.8, 70% yield). The propargylation of AG is less effective in the systems MOH (M = Na, K)/DMSO. DS of propargyl AG reaches 1.8 (70% yield) when propargyl chloride is used as propargylating agent, while with PB under the same conditions DS value does not exceed 0.4-0.6, the yields being 44-65%. Under the action of t-BuOK/DMSO system, the AG propargyl ethers have been isomerized to the corresponding unstable allenyl ethers. AG propargyl ethers with DS 2.0 have been almost exhaustively metallated with Ag_2O/NH_3 system to give AG-Ag acetylides derivatives with Ag/C≡C ratio equaling 0.95.