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A safe and scalable procedure for the synthesis of 2-oxopropanethioamide, an intermediate in the synthesis of a potent β-secretase (BACE-1) inhibitor, from the reaction of acetyl cyanide with hydrogen sulfide gas under continuous-flow conditions has been developed. The toxic gas could be accurately dosed using a mass-flow controller or a peristaltic pump. The reaction proceeded smoothly at room temperature in the presence of a small amount of triethylamine as basic catalyst. After a residence time of 15 min, excellent yield (96%) and purity (>99%) were obtained for the target compound. The high reaction selectivity permitted a simple workup procedure consisting of evaporation of all volatiles.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Evandro de Queiroz, Augusto Knoechelmann, Eliane de Moraes Medeiros, Cesar de Abreu and Nelson de Lima Filho

Abstract  

In this work, in addition to the nitrous acid formed by reactive uptake of nitrogen dioxide (NO2) in water, it is proposed to reduce the nitrous ions levels by amino sulfonic acid (HSO3NH2) in a mechanically agitated reactor. To this end, the following parameters were considered: agitation speed, pH, temperature, initial concentration of the reagents and their stoichiometric ratios. It was observed that the nitrous acid conversion (98.54%) was enhanced in acidic medium (pH < 2.5), obeying a first-order reaction in relation to both reagents. A heterogeneous model for nitrogen production was proposed and the kinetics for the gas–liquid process was formulated, where the kinetic rate constants were in the range of 2.62–5.52 m3 kmol−1 s−1 and the gas–liquid mass transfer coefficients were in the range of 0.00502–0.00825 s−1.

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