Green synthesis of Cyclic imides by Amidation and Cyclisation using Bronsted-Lewis acidic montmorillonite clays

Abstract

The treatment of citric acid to montmorillonite was carried out to modify the acidity and surface characteristics. The clays were characterized using various physico‐chemical techniques such as ICP‐OES, XRD, pyridine FT‐IR, BET Surface area, FE‐SEM, and 27Al‐NMR. The catalytic performance of the acid treated clays were tested for the synthesis of cyclic imides by the amidation of benzene‐1,2‐dicarboxylic acid and various aliphatic and aromatic amines, which is required both Bronsted and Lewis acidity. The role of acidity and pore volumes on the selectivity of cyclic imide, and improvement of accessibility to acid sites to give single cyclic product and their confirmation by Mass and 1H NMR techniques. The comparison of various solid acids for the cyclic imide selectivity and correlation with acid site accessibility give the information of enhanced pore volume lead to cyclisation of amic acid to cyclic imide, by approaching the acid site through the pore generated by the acid treatment.

Continuous-flow dehydrative amidation between carboxylic acids and amines using modified mixed metal oxides as solid acid catalysts

“…Cyclic imides are one of the most attractive classes of highly value-added chemicals especially as elements of engineered plastics or electronic devices when they are converted to polymer form. 28 We also applied our continuous-flow amidation to the construction of cyclic imide structures. Dicarboxylic acids such as succinic acid and phthalic acid should be dissolved in the reaction medium to participate in the flow reaction; indeed, chlorobenzene, which allowed obtaining the corresponding imide in high yield under batch conditions, did not dissolve these acids fully and was not suitable for reactions under continuous-flow conditions.…”