The reaction of primary aromatic amines with alkylene carbonates for the selective synthesis of bis-N-(2-hydroxy)alkylanilines: the catalytic effect of phosphonium-based ionic liquids

Abstract

At T≥ 140 °C, different primary aromatic amines (pX-C(6)H(4)NH(2); X = H, OCH(3), CH(3), Cl) react with both ethylene- and propylene-carbonates to yield a chemoselective N-alkylation process: bis-N-(2-hydroxyalkyl)anilines [pX-C(6)H(4)N(CH(2)CH(R)OH)(2); R = H, CH(3)] are the major products and the competitive formation of carbamates is substantially ruled out. At 140 °C, under solventless conditions, the model reaction of aniline with ethylene carbonate goes to completion by simply mixing stoichiometric amounts of the reagents. However, a class of phosphonium ionic liquids (PILs) such as tetraalkylphosphonium halides and tosylates turn out to be active organocatalysts for both aniline and other primary aromatic amines. A kinetic analysis monitored by (13)C NMR spectroscopy, shows that bromide exchanged PILs are the most efficient systems, able to impart a more than 8-fold acceleration to the reaction. The reactions of propylene carbonate take place at a higher temperature than those of ethylene carbonate, and only in the presence of PIL catalysts. A mechanism based on the Lewis acidity of tetraalkylphosphonium cations and the nucleophilicity of halide anions has been proposed to account for both the reaction chemoselectivity and the function of the catalysts.

Catalytic Transformations of Functionalized Cyclic Organic Carbonates

“…Selva importantly,w ithout any linear carbamate product noted (Scheme 1, path b). [17] TheKleij group recently reported the formation of N-aryl carbamates from aryl amines and cyclic carbonates under ambient conditions in the presence of 1,5,7-triazabicyclo-[4.4.0]dec-5-ene (TBD) as organocatalyst, and most of the reactions could be performed under solvent-free conditions (Scheme 2, path a). [18] The N-aryl carbamate products are potentially useful precursors for N-aryl isocyanates,which are used on al arge scale in the production of polyurethanes.…”

Towards an Understanding of the “Ambiphilic” Character of Ionic Liquids for Green Synthesis of Chemically Diverse Architectures

“…A simple and robust methodology to carry out the bis‐ N ‐hydroxyalkylation of anilines 12 with ethylene carbonate (EC) 13 a and propylene carbonate (PC) 13 b in presence of bromide exchanged phosphonium salts (PILs) as the most efficient organocatalysts was reported by Selva et al (Scheme ) . Several advantages can be associated with the developed methodology from both synthetic and environmental viewpoints for instance (i) the reaction works with variously substituted anilines, PC and EC; (ii) harmful hydroxyalkylating agents such as alkylene oxides or halohydrins have been replaced by non toxic alkylene carbonates; (iii) the reactions are chemoselective with respect to the β carbons of EC and PC while the competitive formation of carbamate products are ruled out.…”

Katalytische Umwandlung von funktionalisierten cyclischen organischen Carbonaten

“…Die Aminolyse von cyclischen Carbonaten durch Alkylamine liefert Alkylcarbamate/Urethane und läuft typischerweise bei Raumtemperatur ohne die Notwendigkeit eines Katalysators ab, [16] wobei allerdings ein Gemisch aus zwei Regioisomeren resultiert (Schema 1, Wega). [17] Die Gruppe um Kleij beschrieb erst kürzlich die Bildung von N-Arylcarbamaten aus Arylaminen und cyclischen Carbonaten bei Umgebungsbedingungen und in Gegenwart des Organokatalysators 1,5,7-Triazabicyclo[4.4.0]dec-5-en (TBD), wobei der Großteil der Reaktionen ohne die Verwendung eines Lçsungsmittels durchgeführt werden konnte (Schema 2, Wega). Selva et al berichteten, dass die Reaktion zwischen Propylencarbonat und Anilin in Gegenwart einer ionischen Flüssigkeit (IL) als Katalysator hohe Te mperaturen (> 140 8 8C) bençtigt und zudem ein komplexes Reaktionsgemisch liefert, ohne dass die Bildung eines linearen Carbamatprodukts zu beobachten war (Schema 1, Wegb).…”