(233aj) Green Synthesis of Carboxylic Acids from Ethyl Acetates Derivatives Using K2CO3 Under Microwave Irradiation

Hernández-Fernández, J., Universidad Autónoma de Nuevo León
Hernández-Fernández, E., Universidad Autónoma de Nuevo León
Rodríguez-Torres, V., Universidad Autónoma de Nuevo León
Tiempos-Flores, N., Universidad Autónoma de Nuevo León
López-Cortina, S., Universidad Autónoma de Nuevo León

Carboxylic acids preparation is frequently required in organic synthesis, because this kind of compounds are key intermediates in the synthesis of amides, oxazolines and other derivatives of biological interest. Therefore, the synthesis of these compounds in a rapid and efficient way and friendly to the environment remains a subject of great interest in organic synthesis. In this work, we describe a simple and efficient synthetic procedure for the preparations of novel carboxylic acids from ethyl esters under microwave irradiations. The protocol described herein is environmentally friendly and allows the preparation of a wide variety of carboxylic acids. Initially we developed a general procedure to prepare the ethyl acetate derivatives (azolyl-acetates and various cinnamic esters analogues) using an ultrasonic oscillator as energy source to facilitate the chemical reactions. Under these conditions (sonication at 40 °C for 3h, in EtOH or DMF and K2CO3) the compounds were obtained with good yields (80-90%). These esters derivatives were then reacted in ethanol, potassium carbonate under microwave irradiation at 180°C using a Microwave Synthesis Reactor (Monowave 300/Anton Paar). All reactions under microwave irradiation were completed within 20 min with high yields (90-98%). The reaction progress was monitored by TLC and the chemical structures of the target compounds were confirmed by 1H, 13C NMR and MS. High Resolution Mass Spectra (FAB) showed the molecular ion for all compounds. The 1H NMR spectra for the cinnamic acids derivatives showed the coupling constants (J) of 16 Hz for the vinylic protons, characteristic for the trans alkenes.