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Gas-phase acylium ion transfer reactions mediated by a proton shuttle mechanism

Authors

  • Eudes E. Fileti,

    Corresponding author
    1. Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo, CEP 09210-270, Brazil
    • Centro de Ciencias Naturais e Humanas, Universidade Federal do ABC, Santo André, São Paulo, CEP 09210-270, Brazil
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  • Anselmo E. De Oliveira,

    1. Instituto de Química, Universidade Federal de Goiás, CP 131, Goiânia.Goiás, CEP 74001-970, Brazil
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  • Nelson H. Morgon,

    1. Instituto de Química, Universidade Estadual de Campinas (UNICAMP), Caixa Postal 6154, Campinas, São Paulo, CEP 13083-970, Brazil
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  • José M. Riveros

    Corresponding author
    1. Institute of Chemistry, University of São Paulo, Caixa Postal 26077, São Paulo, CEP 05513-970, Brazil
    • Institute of Chemistry, University of São Paulo, Caixa Postal 26077, São Paulo, CEP 05513-970, Brazil
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Abstract

The mechanism and the energy profile of the gas-phase reaction that mimics esterification under acidic conditions have been investigated at different levels of theory. These reactions are known to proceed with rate constants close to the collision limit in the gas-phase and questions have been raised as to whether the typical addition-elimination mechanism via a tetrahedral intermediate can explain the ease of these processes. Because these reactions are common to many organic and biochemical processes it is important to understand the intrinsic reactivity of these systems. Our calculations at different levels of theory reveal that a stepwise mechanism via a tetrahedral species is characterized by energy barriers that are inconsistent with the experimental results. For the thermoneutral exchange between protonated acetic acid and water and the exothermic reaction of protonated acetic acid and methanol our calculations show that these reactions proceed initially by a proton shuttle between the carbonyl oxygen and the hydroxy oxygen of acetic acid mediated by water, or methanol, followed by displacement at the acylium ion center. These findings suggest that the reactions in the gas-phase should be viewed as an acylium ion transfer reaction. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

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