Regioselective sulfation of trimethylsilyl cellulose using different SO3-complexes

Trimethylsilyl cellulose (DS_Si = 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 °C, 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 °C, 24 h) the polymers in vacuum.