Synthesis of cyclic amides from dicarboxylic acids and amines using base tolerant heterogenous catalyst

Abstract

Amide is one of the most valued group in current day and the synthesis of amides are assuredly the most cardinal transformation in synthetic organic and medicinal chemistry. By showing diverse activities as an intermediate in the polymer and chemical industries, it is constantly pushing for designing more feasible amides with biological potency as antimitotic and antiviral agents. Conventional methods have been established for synthesizing amides from carboxylic acid derivatives with a stoichiometric amount of condensation reagents. Synthesis of amides from alcohols, aldehydes, and from nitriles have also been reported. But these methods require high temperature and large amount of additives. Besides, several homogeneous catalytic methods have been reported by using precious metal complex catalysts including Au, Pt, Pd, but this homogeneous catalytic method has no reusability for these precious metal and encounter difficulties in catalyst and product separation. Moreover, the use of heterogeneous catalysts such as Nb2O5 have also been reported for the synthesis of amide but it is costly and needs to be calcined at high temperature and it acts only to produce linear diamide. SnO2 is Lewis acid catalyst which activates carbonyl carbon of dicarboxylic acids group and turn -OH groups of dicarboxylic acid into a good leaving group before treatment with diamine. By using the concepts of Lewis acidity of SnO2 , diamides were synthesized from dicarboxylic acids and diamines in presence of o-xylene solvent. Among different types of catalysts SnO2 showed highest catalytic activity to the corresponding 1,1'-(ethane-1,2-diyl)bis(3,4-dihydroxypyrrolidine)-2,5-dione at 143 °C. Succinic acid, malic acid, dl maleic acid, dl tartaric acid, glutaric acid and phthalic acid were found as decisive reactants to produce desired cyclic diamide products with good yields. Finally, after completion of reaction, catalyst was separated from the mixture by centrifugation and dried in oven at 90 °C for 3 hrs. And it was reused for three times with some decrease in percentage of yield. The synthesized amide products were identified by FT-IR, GC-Mass analysis and catalyst by XRD analysis.

To surmount all these stumbling blocks, a general method has been developed for direct synthesis of cyclic amide from dicarboxylic acid and amine for the first tine by using a base tolerant SnO_2 as a heterogeneous catalyst which is readily obtainable, cheaper and recyclable. Keywords: Cyclic diamide, SnO_2, non-calcined, base-tolerant