Synthesis of sulfated alginate from its tributylammonium salt: Comparing the sulfating agents H₂SO₄-DCC and SO₃·py

Direct comparison of the sulfating agents H₂SO₄-DCC and SO₃·py for the synthesis of sulfated alginate (S-Alg) as well as detailed characterisation of the products that form is lacking. This study involving three researchers used the tributylammonium salt of alginate (T-Alg) as a common substrate for the sulfation reactions. It was found that the use of H₂SO₄-DCC resulted in poor control of the degree of sulfation (DS) and that the S-Alg polymers contained nitrogen (determined by elemental analysis) as a result of formation of an unwanted N-acylurea adduct. Additionally, a large reduction in chain length was confirmed. In contrast, the use of SO₃·py gave reasonable control over DS, resulted in high yields, showed no contamination and no clear change in chain length. Detailed characterisation of such S-Alg polymers by ¹H NMR, ¹³C NMR and ¹H,¹³C-HSQC NMR confirmed sulfation at C2 and C3 with a preference for C2.