Microwave‐Assisted Kolbe‐Schmitt Synthesis Using Ionic Liquids or Dimcarb as Reactive Solvents

Abstract

The activation of relatively inert carbon dioxide as a building block for organic products is of interest from both ecological and chemical points of view. One of the few industrially relevant processes using CO 2 is the Kolbe-Schmitt synthesis. Two strategies to obtain the carboxylated product 2,4-dihydroxybenzoic acid from resorcinol are presented: both Dimcarb and hydrogencarbonate-or methylcarbonate-based ionic liquids are employed as reactive solvents in a microwaveassisted reaction. Reaction optimization shows that the ionic liquids are more reactive than Dimcarb. However, Dimcarb offers advantages with regard to ecological aspects, such as the Global Warming and Human Toxicity Potential and the Cumulative Energy Demand, which were assessed as part of the process development.

Environmentally Benign Microreaction Process Design by Accompanying (Simplified) Life Cycle Assessment

“…Experimental data provided by the IMM serve as the basis for case study 1 (see Tab. 1), whereas the results obtained from A. Stark (FSU) are discussed within a corresponding article [32].…”

Flow Chemistry of the Kolbe‐Schmitt Synthesis from Resorcinol: Process Intensification by Alternative Solvents, New Reagents and Advanced Reactor Engineering

“…Such a device is one option for the pilot plant that will be erected and operated on an industrial site at the end of the project. Due to the current hints for an economic reprocessing and recycling of the 1,3-dialkylimidazolium-based reactive ionic liquids [47], the potential of alternative and more environment friendly carboxylating agents will be investigated. It is envisaged to transfer the results gained with the model reaction to an industrially relevant carboxylation reaction.…”

Gaseous Reactants in Microwave‐Assisted Synthesis

“…Otherwise, the applicability of Dimcarb, a mixture of 2 mol HNMe 2 and CO 2 , was investigated. Dimcarb is a liquid under standard conditions and owing to different equilibrium reactions various species exist [46]. Microwave-assisted reactions with the mentioned CO 2 substitutes did not outperform classical procedures with respect to product yield, but interesting conclusions regarding these alternatives were drawn.…”

“…A variant of the Kolbe-Schmitt synthesis was used to assess the applicability of different sources of CO 2 in the transformation of resorcinol to 2,4-dihydroxybenzoic acid [46]. On the one hand, ionic liquids with anions bearing the possibility of acting as CO 2 carrier were tested (MeCO − 3 , HCO − 3 ).…”