Dextran functionalized by 4‐nitrophenyl carbonate groups. Aminolysis reactions

Abstract

The modification reaction of dextran with 4-nitrophenyl chloroformate using pyridine as catalyst was studied. The structure of the resulting polymers was determined by means of IR, 'H and l3C NMR spectroscopy as well as by chemical analysis. Under the used experimental conditions only acyclic carbonate groups have been detected. Preliminary experiments have shown that the reaction of 4-nitrophenyl carbonate groups with several model amines is greatly dependent on the basic character of the amine. Model amino-type drugs (phenethylamine and tyramine) were satisfactorily bound to activated dextran with 4-nitrophenyl carbonate groups. The heterogeneous hydrolysis of dextran-phenethylamine or dextran-tyramine adducts showed that no significant hydrolysis takes place under the applied conditions (PH 1 and pH 9,37 "C). ZUSAMMENFASSUNGDextran wurde mit 4-Nitrophenylchloroformat und Pyridin als Katalysator umgesetzt. Die Struktur der modifizierten Dextrane wurde mittels IR-, 'H-und I3C-NMR-Spektroskopie bestimmt. Unter den gewahlten Reaktionsbedingungen entstehen nur acyclische Carbonate. Vorversuche zeigten, daR die Reaktion der 4-Nitrophenylchloroformat-Gruppen mit verschiedenen Amin-Modellverbindungen stark von der Basizitat des Amins abhangt. Die Anbindung der Modellamine Phenethylamin und Tyramin an das modifizierte Dextran war befriedigend. Die Dextran-Phenethylaminund Dextran-Qramin-Verbindungen sind gegen heterogene Hydrolyse bei 37 "C (pH 9 und pH 1) weitgehend bestandig.

Evaluation of the Synthesis of Soluble Aromatic Cellulose Carbonates of Low Degree of Substitution

“…These cellulose phenyl carbonates could be studied by 2D NMR spectroscopic methods as previously published . The cellulose phenyl carbonates show a characteristic signal for the carbonyl moieties at 153 ppm in 13 C NMR spectra . In Figure , 13 C NMR spectra of cellulose phenyl carbonates 3b,c and 3e with increasing DS values are shown in comparison with the NMR spectrum of cellulose.…”

“…Thus, reaction of cellulose 1 with 4‐nitrophenyl chloroformate as reagent leads to the corresponding cellulose‐4‐nitrophenyl carbonates of high reactivity. Because of the electron‐withdrawing group, the phenyl carbonate moiety possesses an enhanced electrophilic character (compared to the nonsubstituted phenyl ring) yielding an improved attack of nucleophiles including the unmodified hydroxyl groups of the AGU of the same repeating unit or those of other polymer chains . Thus, intra‐ or intermolecular cross‐linking may occur easily, leading to insoluble products in the case of intermolecular reaction ( Figure ).…”

“…Because of the electron-withdrawing group, the phenyl carbonate moiety possesses an enhanced electrophilic character (compared to the nonsubstituted phenyl ring) yielding an improved attack of nucleophiles including the unmodified hydroxyl groups of the AGU of the same repeating unit or those of other polymer chains. [1,11,[19][20][21][22] Thus, intra-or intermolecular cross-linking may occur easily, leading to insoluble products in the case of intermolecular reaction (Figure 2). Furthermore, 4-nitrophenol is formed during the reaction and may be imbedded in the polymer network as impurity.…”

“…Scheme for the a) intra-and b) intermolecular cross-linking of cellulose-4-nitrophenyl carbonate. [20,22] www.advancedsciencenews.com www.mcp-journal.de 1.5 are soluble in THF and above this DS (2.0), they are even soluble in acetone. [11]…”

Free‐radical copolymerization of ethyl α‐hydroxymethylacrylate with methyl methacrylate by reversible addition–fragmentation chain transfer

“…PEHMA modified with 4‐nitrophenyl carbonate groups was synthesized in a homogeneous medium with the method followed in the functionalization of dextran 78…”