Optimization of Ultrasound-Assisted Oxidation of Thiophene Using Phase Transfer Catalyst

Abstract

Thiophene oxidation with hydrogen peroxide was studied with tetrabutylammonium bromide, phenyltrimethylammonium tribromide, ethyltriphenylphosphonium bromide, benzyltrimethylammonium tribromide, tetrapropylammonium bromide, tetrabutylammonium hydrogensulphate, and 18-crown-6-ether as phase transfer catalysts (PTC) under ultrasound. Highest conversion (82.59%) was achieved with benzyltrimethylammonium tribromide at 1,200 rpm and 30 kHz frequency. The effect of parameters such as oxidant-to-sulphur mole ratio, intensity of ultrasound, stirrer speed, catalyst amount, and operating temperature on oxidation was explored by using benzyltrimethylammonium tribromide. Central composite design was chosen for optimization of conversion using temperature, catalyst loading, and molar ratio. The pseudo first-order kinetics with apparent activation energy of 79.55 kJ/mol was established.

GRAPHICAL ABSTRACT

Keywords:

• Phase transfer catalyst
• Thiophene
• Oxidation
• Ultrasound
• Central composite design