Microwave-assisted conditions for the green synthesis of thioacetamide. Optimization of reaction parameters using response surface methodology

Abstract

An optimized method for the synthesis of thioacetamide (TA) in relation to the consumption of materials and energy, which reduces the production of waste and minimizes costs, is hitherto presented. The most important highlight of this work is the use of an inexpensive and readily accessible reactant for the thionation process (i.e. phosphorus pentasulfide, P4S10), combined with both alumina as solid support and a non-conventional microwave (MW) irradiation technique. In addition to this, Response Surface Methodology (RSM) was used to optimize the entire procedure of the synthesis for simultaneous tripled-maximization of Yield (ε), Mass Intensity (MI) and Mass Productivity (MP). Acetamide (AC)/P4S10 molar ratio, time and temperature of reaction were chosen as independent variables; while ε MI and MP were chosen as responses. The determination of these green metrics parameters allow to evaluate the sustainability of the reaction and compare with other methodologies. A quadratic regression model was derived with satisfactory prediction. Tripled optimization with desirability function predicts a maximum ε of 100%, maximum MI of 29.00 kg/kg and a maximum MP of 3.45% under the following experimental conditions: AC/P4S10 molar ratio of 2.10, time of irradiation of 14 min and a temperature 140 °C.