In situ monitoring of cellulose etherification in solution: probing the impact of solvent composition on the synthesis of 3-allyloxy-2-hydroxypropyl-cellulose in aqueous hydroxide systems†
Etherification of cellulose using allyl glycidyl ether was carried out in aqueous alkaline solutions of benzyltrimethylammonium hydroxide, tetramethylammonium hydroxide, NaOH and different mixtures of these bases in order to study the effect of hydroxide base composition on the course of the reaction and the resulting product properties. In situ FTIR spectroscopy and time sweep shear measurements were carried out to monitor the reactions in real time. Infrared Attenuated Total Reflectance Spectroscopy and 1H NMR confirmed the synthesis of 3-allyloxy-2-hydroxypropyl-cellulose and 2D HSQC NMR confirmed substitution on C2, C3 and C6 in all of the solvents. Quantitative 13C NMR was used to estimate the molar substitution. Cellulose solutions in these quaternary ammonium hydroxides showed higher stability at 50 °C during the course of reaction, faster dissolution and hydrolysis of allyl glycidyl ether and lower molar substitution values compared to NaOH. Even though the highest molar substitution value was obtained in NaOH, the isolated product from this medium had lower solubility in DMSO-d6 and its 13C NMR did not differ significantly except for higher intensity of C1 and C6 compared to the other spectra. The obtained results indicated a more pronounced cascade reaction on the substitution itself in NaOH and lower temperature stability of cellulose solutions in this solvent.