Modification of polygalacturonic acid hydroxyls with trimethylammonium- and/or sulfonate-2-hydroxypropyl group

Polygalacturonic acid (PGA) was quaternized with 2,3-glycidyltrimethylammonium chloride (GTMAC) and/or sulfonated with 3-chloro-2-hydroxy-1-propanesulfonate (CHPS) under vacuum or at ambient pressure in the absence or presence of NaOH. The aim was to find out what optimal ratio of reactants are required to obtain the highest possible degree of substitution (DS), yield and molar masses. The highest DS of PGA obtained (calculated on a fully substituted derivate) for quaternized sample was around one according to elemental analyses. At ambient pressure the DS was lower than under a vacuum treatment. Lower DS and yield (36%) of PGA were obtained when PGA was sulfonated. At ambient pressure the sulfonation has not taken place. Repeated quaternization of PGA has not increased the DSs of PGA, while sulfonation was beneficial for increase of DS. When PGA was modified simultaneously with both alkylating agents, the yield of PGA was further improved (up to 52%). Further, the DS of the ammonium substituent was higher than that of the sulfonate group, and the yield of molar mass of the modified PGA was the highest from all tested experiments. At ambient pressure the DS of PGA treated with both reagents was lower than under vacuum. The treatment of PGA with NaOH at the absence of GTMAC or CHPS caused Mw decrease to 11,150 g/mol, while when quaternized in the absence of NaOH the values were between 20,940 and 32,540 g/mol. The repeated quaternization caused even more dramatic decrease of molar mass (to 6400 g/mol). According to NMR both C-2 and C-3 positions of PGA were substituted equally due to a use of the alkylating reagent or a certain charge.