Enzymatic synthesis of novel pyrrole esters and their thermal stability

Abstract

Abstract In the present work a simple enzymatic approach (Novozym 435) for transesterification to synthesize pyrrole esters was reported. To generate the best reaction conditions, which resulted in the optimum yield of 92%, the effects of lipase type, solvent, lipase load, molecular sieves, substrate molar ratio of esters to alcohol, reaction temperature, reaction duration, and speed of agitation were evaluated. The range of alcohols was assessed under optimal circumstances. The spectrum observations conclusively demonstrated that the compounds could be generated with high yield under the circumstances utilized for synthesis. The odor characteristics of the pyrrolyl esters obtained were examined by gas chromatography–mass spectrometry-olfactometry (GC–MS–O). Among them, compounds of benzhydryl 1H-pyrrole-2-carboxylate (3j), butyl 1H-pyrrole-2-carboxylate (3k) and pentyl 1H-pyrrole-2-carboxylate (3l) present sweet and acid aroma. In addition, the thermal degradation process was further studied using the Py–GC/MS (pyrolysis–gas chromatography/mass spectrometry), TG (thermogravimetry), and DSC (differential scanning calorimeter) techniques. The outcomes of the Py–GC/MS, TG, and DSC techniques show that they have excellent thermal stability.

Keywords

• Pyrrolyl esters
• Novozym 435
• Transesterification
• GC–MS–O
• Py–GC/MS
• TG