title: Kinetics and mechanisms of the unimolecular elimination of 2,2-diethoxypropane and 1,1-diethoxycyclohexane in the gas phase: experimental and theoretical study.
abstract: The gas-phase thermal elimination of 2,2-diethoxypropane was found to give ethanol, acetone, and ethylene, while 1,1-diethoxycyclohexane yielded 1-ethoxycyclohexene and ethanol. The kinetics determinations were carried out, with the reaction vessels deactivated with allyl bromide, and the presence of the free radical suppressor cyclohexene and toluene. Temperature and pressure ranges were 240.1-358.3 °C and 38-102 Torr. The elimination reactions are homogeneous, unimolecular, and follow a first-order rate law. The rate coefficients are given by the following Arrhenius equations: for 2,2-diethoxypropane, log k(1) (s(-1)) = (13.04 ± 0.07) - (186.6 ± 0.8) kJ mol(-1) (2.303RT)(-1); for the intermediate 2-ethoxypropene, log k(1) (s(-1)) = (13.36 ± 0.33) - (188.8 ± 3.4) kJ mol(-1) (2.303RT)(-1); and for 1,1-diethoxycyclohexane, log k = (14.02 ± 0.11) - (176.6 ± 1.1) kJ mol(-1) (2.303RT)(-1). Theoretical calculations of these reactions using DFT methods B3LYP, MPW1PW91, and PBEPBE, with 6-31G(d,p) and 6-31++G(d,p) basis set, demonstrated that the elimination of 2,2-diethoxypropane and 1,1-diethoxycyclohexane proceeds through a concerted nonsynchronous four-membered cyclic transition state type of mechanism. The rate-determining factor in these reactions is the elongation of the C-O bond. The intermediate product of 2,2-diethoxypropane elimination, that is, 2-ethoxypropene, further decomposes through a concerted cyclic six-membered cyclic transition state mechanism.
authors.affiliation: Centro de Química, Instituto Venezolano de Investigaciones Científicas (I.V.I.C.), Apartado 21827, Caracas 1020.A, Venezuela.
authors.forename: Felix
authors.initials: F
authors.lastname: Rosas
authors.forename: Alexis
authors.initials: A
authors.lastname: Maldonado
authors.forename: Jesus
authors.initials: J
authors.lastname: Lezama
authors.forename: Rosa M
authors.initials: RM
authors.lastname: Domínguez
authors.forename: José R
authors.initials: JR
authors.lastname: Mora
authors.forename: Tania
authors.initials: T
authors.lastname: Cordova
authors.forename: Gabriel
authors.initials: G
authors.lastname: Chuchani
mesh_terms: D003510:Cyclohexanes / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D007700:Kinetics; D015394:Molecular Structure; D011407:Propane / Q000031:analogs & derivatives* / Q000737:chemistry; D011789:Quantum Theory
chemical_list: D003510:Cyclohexanes; D005740:Gases; C571808:2,2-diethoxypropane; C571807:1,1-diethoxycyclohexane; D011407:Propane