Regioselective sulfation of trimethylsilyl cellulose using different So3-complexes

Trimethylsilyl cellulose (DSSi = 2.9) dissolved in dry tetrahydrofurane was reacted with SO3-complexes of N,N-dimethylformamide, triethylamine, pyridine and ethyldiisopropylamine. Under the given reaction conditions, i.e. 25 degreesC, 24 h, 2.2 mol equivalent SO3-complex, the SO3 attacks the trimethylsilyl ether groups followed by the formation of sodium sulfate cellulose under sodium hydroxide work-up conditions. The regioselectivity of the sulfation is controlled by the complex partner of SO3. Cellulose sulfates with preferred O-6 sulfation were obtained using SO3-N,N-dimethylformamide. In case of SO3-triethylamine, cellulose-2-sulfates could be prepared with good regioselectivity. Small residual amounts of silicon in the cellulose sulfates (0.1 - 0.2% w/w) can be quantified using inductively coupled plasma-optical emission spectroscopy (ICP-OES), and can be decreased up to 80% by heating (70 degreesC, 24 h) the polymers in vacuum