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Eco‐Friendly Methodology for the Formation of Aromatic Carbon–Heteroatom Bonds by Using Green Ionic Liquids
Author(s) -
Richards Kenza,
Petit Eddy,
Legrand YvesMarie,
Grison Claude
Publication year - 2021
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.202003827
Subject(s) - chemistry , reagent , bromine , ionic liquid , heteroatom , halogenation , electrophile , ionic bonding , organic chemistry , solvent , environmentally friendly , green chemistry , inorganic chemistry , electrophilic aromatic substitution , ring (chemistry) , ion , catalysis , biology , ecology
A new sustainable method is reported for the formation of aromatic carbon–heteroatom bonds under solvent‐free and mild conditions (no co‐oxidant, no strong acid and no toxic reagents) by using a new type of green ionic liquid. The bromination of methoxy arenes was chosen as a model reaction. The reaction methodology is based on only using natural sodium bromine, which is transformed into an electrophilic brominating reagent within an ionic liquid, easily prepared from the melted salt FeCl 3 hexahydrate. Bromination reactions with this in‐situ‐generated reagent gave good yields and excellent regioselectivity under simple and environmentally friendly conditions. To understand the unusual bromine polarity reversal of sodium bromine without any strong oxidant, the molecular structure of the reaction medium was characterised by Raman and direct infusion electrospray ionisation mass spectroscopy (ESI‐MS). An extensive computational investigation using density functional theory methods was performed to describe a mechanism that suggests indirect oxidation of Br − through new iron adducts. The versatility of the methodology was successively applied to nitration and thiocyanation of methoxy arenes using KNO 3 and KSCN in melted hexahydrated FeCl 3 .