Abstract
This paper proposes a convenient route to oxidize the –CH2–OH groups in the water-soluble pullulan, using a new catalytic polymer-supported N-hydroxyphthalimide (NHPI) immobilized on polystyrene. The protocol involves the presence of sodium hypochlorite and sodium bromide. The conversion is possible at room temperature, atmospheric pressure, and pH = 10. The characterization of both the catalysts and oxidized pullulan was done using NMR and FTIR methods. Using polyelectrolyte titration with end-point indication by means of a particle-charge detector (PCD), we were able to assess the degree of electrokinetic charge in all oxidized samples as a consequence of the conversion of the –CH2–OH group into –COOH moieties. The possibility of recovery and recycling of the polymer-supported NHPI catalyst was tested for up to four cycles, since the morphological analyses performed on the catalysts using SEM revealed no significant changes.
Highlights
Natural polymers to be used in different applications must often undergo chemical transformations.Among these transformations, oxidation presents a convenient approach to the alteration of the polysaccharide backbone by introduction of new functionalities, such as aldehyde or carboxyl groups, due to its relative simplicity and selectivity
N-hydroxyphthalimide immobilized polystyrenes via amide orcatalysts ester bonds been oxidation, which was chosen as acatalysts model polysaccharide due to its excellent waterchosen solubility, employed as a new class of for pullulan oxidation, which was as aallowing model the easiness of the work-up reaction.water
NHPI was successfully immobilized on polymer supports via amide or ester bonds according to the procedure reported in [20] (Figure 2)
Summary
Natural polymers to be used in different applications must often undergo chemical transformations. In. TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy), and oxidant a primary oxidant suchhypochlorite as sodium hypochlorite this process, the nitrosonium is the key salt species resulting from resulting the conversion of the nitroxyl radical (NaOCl). N-hydroxyphthalimide immobilized polystyrenes via amide orcatalysts ester bonds been oxidation, which was chosen as acatalysts model polysaccharide due to its excellent waterchosen solubility, employed as a new class of for pullulan oxidation, which was as aallowing model the easiness of the work-up reaction.water. In this way, we expanded the easiness use of solid catalysts based on NHPI polysaccharide due to its excellent solubility, allowing the of the work-up reaction. The possibility of recovery and recycling of the catalysts has been evaluated
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