Mechanistic and kinetic study on the reaction of thiophene with hydroxyl radical

In order to understand the thiophene with hydroxyl reaction mechanism and kinetics, we carried out a detailed potential energy surface (PES) on the title reaction at the M06-2X/6-311++G(d,p) and G3 (MP2) (single-point) levels. Two possible reaction mechanisms including addition-elimination and H-abstract were revealed. The hydrogen abstraction of thiophene by OH, produces H2O along with the 2-thienyl (h-P1) or 3-thienyl (h-P2) radicals via a barrier of 7.9 and 2.2 kcal/mol, respectively. The addition of OH to the carbon atoms of the thiophene ring (at either alpha or beta reaction sites) proceeds to intermediates IM1 and IM2 via barrier of 3.4 and 4.7 kcal/mol, and then decompose to the final products, respectively. Multichannel RRKM calculations have been carried out for the total and individual rate constants for all the channels over a wide range of temperatures and pressures. At atmospheric pressure with Ar, N-2 and He as bath gases, IM1 formed by collisional stabilization is dominated at T <= 600 K, whereas P1 produced by addition/elimination pathway are the major products at the temperatures between 700 and 1000 K; the direct hydrogen abstraction leading to H2O with 3-thienyl (h-P2) plays an important role at higher temperatures. (C) 2016 Elsevier B.V. All rights reserved.