Document Type : Original Research Article

Authors

• Oluwaseun Esan Timothy ¹
• Oluwatoba Emmanuel Oyeneyin ^{1, 2}
• Eric Oluwafisayo Akintemi ³
• Adejoro Ajibade Isaiah ¹
• Adeleke Babatunde B ¹

¹ Department of Chemistry, University of Ibadan, Ibadan, Oyo State, Nigeria

² Theoretical and Computational Chemistry Unit, Department Chemical Sciences, Adekunle Ajasin University, Akungba-Akoko, Ondo State, Nigeria

³ Department of Physical Sciences, Wesley University, P.M.B. 507, Ondo, Ondo State, Nigeria

Abstract

The gas-phase elimination reaction of O-isopropyl S-methyl dithiocarbonate was studied using density functional theory with a hybrid B3LYP correlation with large 6-31G*, 6-311+G** basis sets. Calculated values of the activation and thermodynamics parameters for the thermal breakdown were estimated at 623.0K at interval of 25K. The entropy change was ∆S = (-29.842) and (-28.48) J/mol/K; free energy change ∆G = 181.491 and 131.164kJ/mol and enthalpy change ∆H_reaction = 162.808 and 113.720kJ/mol; activation energy E_a = 167.988 and 118.897kJ/mol; Arrhenius factor A = 3.56x10¹¹ and 4.20x10¹¹ and rate constant k = 1.4 x 10^-2 and 2.9 x 10^-3, 4.45x10^-1S^-1 compared well with the experimental results at 623K ∆S(-29.842J/mol/K) ∆G= (181.491kJ/mol) , ∆H = (162.808 kJ/mol),  Ea = (167.988 kJ/mol) , A = (3.56x10¹¹) rate constant k = (1.4 x 10^-2). The results showed the influence of electron donating group on the kinetics and thermodynamics parameters of xanthates. It affirms concertedness of the elimination mechanism via a two-step reaction. The first being the liberation of ethylene an intermediate (methyl dithiocarbonate) through a 6-membered transition state (TS). The second step involves decomposing the intermediate through 4-membered cyclic TS to produce carbonylsulphide and thiol which involves a C-H and C-O bond breaking and S-H bond formation. Intrinsic reaction coordinate (IRC) calculation was done on each of the TS structures to verify that they each connect to their respective minima. Wilberg bond index was employed to monitor the reaction progress and it shows that the TS possess ‘an early’ character closer to the reactant than the products

Graphical Abstract

Keywords

• Kinetics
• ethyldithiocarbonate
• semi-empirical
• ab-initio
• transition state
• Xanthates

20.1001.1.27169634.2021.3.1.1.9

Main Subjects

• Chemistry (Analytical, Organic, Inorganic and Physical Chemistry)