Document Type: Original Research Article

Authors

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

10.33945/SAMI/AJCB/ajcb.2020.236591.1051

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 ∆Hreaction = 162.808 and 113.720kJ/mol; activation energy Ea = 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

Main Subjects

References

 [1] N. Levine, Ira Quantum Chemistry. Englewood Cliffs, New jersey: Prentice Hall. (1991). 455–544. ISBN 978-0-205-12770-2.

 [2] G. Parr., D. P. Robert.; I. G. Craig.; Ross, "Molecular Orbital Calculations of the Lower Excited Electronic Levels of Benzene, Configuration Interaction included". Journal of Chemical Physics. 18 (1950) 1561–1563.

 [3] Leach, Dr Andrew. Molecular Modelling: Principles and Applications (2 ed.). Harlow: Prentice Hall. (2001).

 [4] P. Schlexer. Computational Modeling in Heterogenous Catalysis. Elsevier. (2017). DOI: 10.1016/B978-0-12-409547-2.14273-8

 [5] R.G. Parr. "On the genesis of a theory". Int. J. Quantum Chem. 37 (1990) 327–347.

 [6] A. Al. Etaibi., E John., M. R Ibrahim., N. A. Al-Awadi., Stereoselective synthesis of dihydrothiadiazinoazines and dihydrothiadiazinoazoles and their pyrolytic desulfurization ring contraction Tetrahedron Vol. 67 (2011) 6259-6274.

 [7] E.V. Anslyn, D. A. Dougherty. Mordern physical organic chemistry-University Science books. (2004) 1-1952.

 [8] P. Wu., J. Truong., Y .Huang., J.Li, Regioselectivity Investigation For The Pyrolysis Of Xanthates:  Computational study. Journal of theoretical and computational chemistry. Vol.12 (2013) 1350064.

 [9] E. Velez, J. Quijano, R. Notario, E. Pabon, J. Murillo, J. Leal, E. Zapata, G. Alarcon. A computational study of stereospecifity in the thermal elimination reaction of methyl benzoate in the gas phase, Journal of Physical Organic Chemistry 22 (2009) 971.

 [10] N. AL-Awadi, D.B. Bigley. Carbonate Pyrolysis. Part 6. The kinetics and mechanism of the pyrolysis of Thion and Dithio-carbonates implications for the Transition state in carbonate pyrolysis. J. Chem. Soc. Perkin Trans. 2 (1982) 773-775.

 [11] O.O. Adeboye ., The kinetics and thermodynamics of the Diels-Alder reaction of acrolein and 1, 3-butadiene to produce 3-cyclohexenecarboxaldehyde (1, 2, 3, 6Tetrahydrobenzaldehyde), a fragrance and masking ingredient used in many skin care products was modelled in the gas-phase. Journal of Chemical Society of Nigeria 44 (2019) 1095 -1105.

 [12] I.M. Mc-Aplpine. Name Reactions of functional group Transformation Journal of Chemical Society 906 (1930) 15114-15123.

 [13] H.E. O’Neal, S.W. Benson. A Method for Estimating the Arrhenius A factors for Four- and Six-centre Unimolecular Reactions, J. Phys. Chem. 71 (1967) 2903 - 2921.

 [14] N. Al-Awadi. The mechanism of Thermal Elimination. Part 24. Elimination From Mono Di and Trithiocarbonates. The Dependence of the Transition State polarity, Thione to Thiol Rearrangement and Ether Formation via Nucleophilic Substitutions. J. Chem. Soc. Perkin Trans. 2, (1988) 197-182.

 

 [15] I. A. Adejoro, T. O. Bamkole. Semi-empirical quantum mechanical, molecular orbital method using MOPAC, calculation of the Arrhenius parameters for the pyrolysis of some alkyl acetates. J. Appl. Sci., 5 (2005).  1559-1563.

 [16] O.O.  Adeboye, I.A. Adejoro, A. M. Olatunde. Computational Modelling of the Kinetics and Thermodynamics of Diels-Alder reaction: 1,3-cyclohexadiene and substituted ethene. Leonardo Electronic Journal of Practices and Technologies. (2018). 33, July-December 207-218.

 [17] A.C West, M.W Schmidt, M.S Gordon, K. Ruedenberg. A Comprehensive Analysis in Terms of Molecule-Intrinsic Quasi-Atomic Orbitals. IV. Bond Breaking and Bond Forming along the Dissociative Reaction Path of Dioxetane. The Journal of Physical Chemistry A.  119 (2015)10376–10389.

 [18] I. A. Adejoro, T. O. Esan., O. O Adeboye, B. B Adeleke. Quantum mechanical studies of the kinetics, mechanisms and thermodynamics of gas-phase thermal decomposition of ethyl dithiocarbonate (xanthate). Journal of Taibah University for Science, 11 (2017) 700–709.

 [19] G. Sudhakar, B. Rajakumar. Thermal decomposition of 1-chloropropane behind the reflected shock waves in the temperature range of 1015–1220 K: Single pulse shock tube and computational studies. Journal of Chemical Sciences, 126 (2014) 897–909.

 [20] W.J. Hehre. Guide to Molecular Mechanics and Quantum Chemical Calculations Hardcover. (2003).

 [21] J.W. Mclver Jr, A. Kormonicki. Rapid Geometry optimization for Semi- Empirical molecular Orbital Methods. Chem. Phys. Letts. 10 (1971) 303.

 [22] S.W. Benson. The foundations of chemical kinetics, Mcgraw-Hill, New York 1-30 of 79 (1960).

 [23] A. Moyano, M.A. Pericas, E. Valenti. A theoretical study on the mechanism of the thermal and the acid-catalysed decarboxylation of 2-oxetanones (beta lactones) J. Org. Chem. 54 (1989) 573-582

 [24] R. Taylor. The mechanism of thermal elimination. Journal of Chemical Society, Perkin Transaction. 2 (1983) 291-296.

 [25] V.M. Lee, M. J. Carden, W.W. Schlaepfer, J. O. Trojanowski. Monoclonal antibodies distinguish several differentially phosphorylated states of the two largest rat neurofilament subunits (NF-H and NF-M) and demonstrate their existence in the normal nervous system of adult rats. J. Neurosci., 7 (1987) 3474-3488.

 [26] R.F.W. Bader, A.N. Bourns. A kinetic isotope effect study of the Tschugaeff reaction, Canadian Journal Chemistry 3 (1961)  348-358.

 [27] W. Huckel, W. Tappe, G. Legutke. Abspaltungsreaktionen und ihr sterischer verlauf, Ann. 543  (1940) 191.

 [28] O.O. Adeboye. Computational Modelling of the Mechanisms, Kinetics and Thermodynamics of Pyrolysis of Isobutyl Bromide in the Gas-Phase. Chemical Science International Journal  18 (2017) 1-9