Raman and NMR kinetics study of the formation of amidoamines containing N-hydroxyethyl groups and investigations on their Cu(II) complexes in water

Abstract

Three amidoamines containing the N-hydroxyethyl group (^HOEt), namely (^HOEt)₂N(CH₂)₂C(O)NH₂ (1), [(^HOEt)₂N(CH₂)₂C(O)NH]₂CH₂ (2) and ^HOEtN[(CH₂)₂C(O)NH₂]₂ (3) have been synthesized by reacting diethanolamine ^HOEt₂NH with acrylamide and N,N'-methylenebisacrylamide (respectively 1 and 2) and ethanolamine ^HOEtNH₂ with acrylamide (3). Four other compounds corresponding to 1 and 2, but derived from sec-amines Me₂NH (4 and 5) and Et₂NH (6 and 7) have been prepared for the sake of comparison of the spectroscopic features. All compounds have been obtained by the well-known aza-Michael addition between an N-nucleophile and an activated vinyl group. The reaction in water between diethanolamine and acrylamide leading to 1 has been monitored in situ by Raman and NMR spectroscopy, both techniques confirming second order kinetics and giving values for kinetic constants in excellent agreement. The coordination ability of 1 and 2 towards Cu²⁺ in water has been studied by the Job's plot method. Spectroscopic data indicate that ligand 1 prevalently forms a 4:1 Ligand/Metal complex with a (N,O₃) coordination set on the equatorial plane of Cu²⁺, whereas ligand 2, containing two amide functionalities bridged by a methylene group, appears able to form a 1:1 Ligand/Metal chelate species, again with a (N,O₃) donor set around copper.

Keywords: Amidoamines; Copper complexes; Job's plot; Raman monitoring; Reaction kinetics; aza-Michael addition.