Carboxymethyl cellulose (CMC) was treated in a dipolar-aprotic solvent like N,N-dimethylacetamide, or dimethylsulfolxide (DMSO) with p-toluenesulfonic acid yielding a high reactive gel-suspension of the polymer. This mixture allows a direct esterification of free hydroxyl groups of CMC as exemplified by acylation with carbonic acid chlorides, or anhydrides, and with isocyanates as well as by sulphation, phosphating and silylation. The products characterized by elemental analysis and FTIR spectroscopy possess a high degree of functionalization.