In situ Acidic Carbon Dioxide/Ethanol System for Selective Oxybromination of Aromatic Ethers Catalyzed by Copper Chloride

Abstract

An environmentally benign carbon dioxide/ethanol reversible acidic system was developed for the copper(II)‐catalyzed regioselective oxybromination of aromatic ethers without the need of any conventional acid additive and organic solvent. Good to excellent yields together with very good regioselectivity were achieved when easily available cupric chloride dihydrate was used as catalyst and lithium bromide as the cheap and easy‐to‐handle bromine source under supercritical carbon dioxide conditions. Notably, the catalytic system worked well for a wide range of aromatic ethers including sulfides, resulting in the formation of the mono‐brominated products in high yields and exclusive regioselectivity. The alkylcarbonic acid in situ formed from ethanol and carbon dioxide is assumed to play the crucial role in the Brønsted acid‐promoted reaction, which could probably act as the proton donator, and was studied employing in situ FT‐IR technique under carbon dioxide pressure by monitoring the vibration shift of the hydroxy group of ethanol. Given with excellent bromine atom efficiency as well as no need of neutralization in waste disposal, this approach thus represents a greener pathway for the aerobic bromination of aromatic ethers. A possible catalytic cycle for the in situ alkylcarbonic acid‐assisted oxybomination and the effect of supercritical carbon dioxide, i.e., activation of alcohol and enhancement of mass transfer are also discussed.

A biphase H2O/CO2system as a versatile reaction medium for organic synthesis

“…They also studied copper(II)-catalyzed regioselective oxybromination of aromatics in CO 2 /ethanol system. 187 Good to excellent yields as well as very good regioselectivity were achieved (CO 2 1 MPa, O 2 1 MPa, 100 C, 10 h). The authors believed that formation of ethylcarbonic acid was crucial for the promotion of the reaction.…”

Valorization of rice bran: Modified supercritical CO2 extraction of bioactive compounds

“…by SC-CO2 with ethanol as cosolvent (in variable proportions in the range 30 to 70%) at 80 °C and 25 MPa, concluding that ethanol increased in all the cases the oil recovery rate and Belayneh et al [29] pumped ethanol at concentrations of 2.5, 5 and 10% (mass rate of ethanol/mass rate of SC-CO2) into the extraction vessel, loaded with Camelina sativa seeds. These authors reported a significant increase in the extraction yield at all pressure and temperature levels (35)(36)(37)(38)(39)(40)(41)(42)(43)(44)(45) MPa; 50-70 °C, respectively). This increase in oil extraction yield is, in general, attributed to the increase in the polarity of the solvent mixture as a consequence of the addition of ethanol.…”

“…All in all, this work, as a first step in a comprehensive valorization of rice bran using pressurized fluids, the study of the extraction of bioactive molecules and oil from rice bran using SC-CO2 and ethanol as cosolvent is carried out. The effect of the main process parameters temperature (40-60 °C), pressure (30)(31)(32)(33)(34)(35)(36)(37)(38)(39)(40) and percentage of ethanol as cosolvent (from 0% (neat SC-CO2) to 10%) on the quality of the oil has been studied. The extracted oils have been completely characterized in terms of fatty acids profile and content in bioactive molecules such as polyphenols, flavonoids, oryzanols and tocopherols.…”

Reduction of sulfoxides and pyridine-N-oxides over iron powder with water as hydrogen source promoted by carbon dioxide

“…In this context, CO 2 chemistry based on its capture and utilization deserves much attention and great efforts from the scientific community and industrial sectors. [2][3][4][5][6][7] On the other hand, CO 2 as an abundant and readily available C 1 resource has also shown significant potential and advantage in synthetic organic chemistry for production of value-added chemicals. [8][9][10][11][12] Besides profound achievements in chemical fixation of CO 2 , various feasible uses of CO 2 have been widely proposed, such as a sound reaction medium for green processes, 13 Lewis acid catalyst and/or promoter, 14 and tunable reagent for controlling chemical selectivity, 15 providing feature advantages from the viewpoint of green chemistry.…”