title: Two competing reactions of tetrabutylammonium alginate in organic solvents: Amidation versus γ-lactone synthesis.
abstract: Biocompatibility and thickening properties predetermine alginates as ingredients in food, cosmetic and pharmaceutical products. Further chemical modifications are often desired for a product optimization. The introduction of hydrophobic groups can be realized by employing organic tetrabutylammonium alginate (TBA-Alg) solutions. The synthesis of alginic acid alkyl amides from TBA-Alg with 2-chloro-1-methylpyridinium iodide (CMPI) as a coupling agent, however, has so far not resulted in a high degree of amidation. The analysis of the coupling reaction revealed the formation of mannuronic acid γ-lactone structures, which required a conformation change from (1)C4 to (4)C1. The opening of the γ-lactone required a high excess of butylamine. In the case of CMPI, triethylamine had to be added prior to the coupling agent in order to suppress the assumed alginic acid formation. The degrees of amidation achieved were up to 0.8, and for propylphosphonic anhydride as the coupling agent up to 1. The molecular weights of the alginic acid butyl amide were ≥35kDa.
authors.affiliation: Environmental Research and Innovation Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg. Electronic address: thomas.schleeh@list.lu.
authors.forename: Thomas
authors.initials: T
authors.lastname: Schleeh
authors.affiliation: Environmental Research and Innovation Department, Luxembourg Institute of Science and Technology, 41 rue du Brill, L-4422 Belvaux, Luxembourg.
authors.forename: Mathieu
authors.initials: M
authors.lastname: Madau
authors.affiliation: Wyatt Technology Europe GmbH, Hochstrasse 12a, D-56307 Dernbach, Germany.
authors.forename: Dierk
authors.initials: D
authors.lastname: Roessner
keywords: 2-Chloro-1-methylpyridinium iodide; Alginic acid alkyl amide; Conformation change; Mannuronic acid γ-lactone; Propylphosphonic anhydride