Several mechanisms in the elimination kinetics of ω‐chlorocarboxylic acids in the gas phase

Chuchani, Gabriel; Martín, Ignació; Rotinov, Alexandra; Domínguez, Rosa M.; Milagros, Perez I.

doi:10.1002/poc.610080302

Cited by 17 publications

(11 citation statements)

References 15 publications

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“…The mechanism for the gas-phase elimination of 2-substituted chlorocarboxylic acids [1,2] was described in terms of a semi-polar five-membered cyclic transition state, where the acidic H of the COOH assisted the leaving Cl atom, followed by the carboxylic oxygen participation in the stabilization of the incipient positive carbon atom (reaction 1, Path 1) to give the corresponding ␣-lactone. This unstable lactone intermediate decomposed into the corresponding carbonyl compound and CO gas [reaction (1)].…”

Section: Introductionmentioning

confidence: 99%

Kinetics of the gas-phase elimination of ?-Bromophenylacetic acid under maximum inhibition

Chuchani¹,

Domínguez²

1999

Int. J. Chem. Kinet.

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The gas phase elimination kinetics of the title compound was studied over the temperature range of 260.1-315.0ЊC and pressure range of 20-70 Torr. This elimination, in seasoned static reaction system and in the presence of at least fourfold of the free radical inhibitor toluene, is homogeneous, unimolecular and follows a first-order rate law. The reaction yielded mainly benzaldehyde, CO, and HBr, and small amounts of benzylbromide and CO 2 . The observed rate coefficients are expressed by the following Arrhenius equations: The mechanisms are believed to proceed through a semi-polar five-membered cyclic transition state for the benzaldehyde formation, while a four-centered cyclic transition state for benzylbromide formation.

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Section: Introductionmentioning

confidence: 99%

Kinetics of the gas-phase elimination of ?-Bromophenylacetic acid under maximum inhibition

Chuchani¹,

Domínguez²

1999

Int. J. Chem. Kinet.

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“…The kinetics of the gas phase decomposition of several carboxylic acid derivatives has been experimentally studied by Chuchani and co-workers. − The results prove the reaction to be homogeneous, to be unimolecular, and to obey a first-order rate law. In particular, the rate coefficient for the gas phase decomposition of 2-chloropropionic acid (CH 3 CHClCOOH) to form hydrogen chloride, carbon monoxide, and acetaldehyde has been determined 1 at relatively low pressure and expressed as a function of temperature by the following Arrhenius-type equation: …”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

et al. 1997

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The reaction mechanism for the decomposition of 2-chloropropionic acid in the gas phase to form hydrogen chloride, carbon monoxide, and acetaldehyde has been theoretically characterized. Analytical gradients have been used by means of AM1 and PM3 semiempirical procedures and ab initio methods at HF and DFT (BLYP) levels with the 6-31G** basis set. The correlation effects were also included by using the perturbational approach at the MP2 level with the 6-31G** and 6-31++G** basis sets and the variational approach at the CISD/6-31G** level and by means of MCSCF wave functions with a (6,6) complete active space and the 6-31G** basis set. The global potential energy surface has been studied, and the stationary points were localized and characterized. The geometries, electronic structure, and transition vector associated with the transition structures have been analyzed and the dependence of these properties upon theoretical methods is discussed. The present study points out, in agreement with the experimental data, that the decomposition process occurs through a two-step mechanism involving the formation of the R-propiolactone intermediate. The transition structure associated with the first step can be described as a five-membered ring with participation of leaving chloride and hydrogen, assisted by the carbonyl oxygen of the carboxyl group. The second transition structure, controlling the R-propiolactone decomposition step, yields the formation of CO and CH 3 CHO molecules. The rate constants and the Arrhenius preexponential factors for the different interconversion steps have been calculated in terms of the transition state theory. The comparison of experimental and theoretical values for these parameters allows us to prove the validity of theoretical methods. The results suggest that the process must be considered as essentially irreversible, the first step being the rate-determining step. From a computational point of view, the inclusion of the correlation energy at the MP2/6-31G** level is necessary to obtain an accurate calculation of the kinetic parameters.

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“…The kinetics of the gas phase decomposition of several carboxylic acid derivatives has been experimentally studied by Chuchani and co-workers. − The results prove the reaction to be homogeneous, to be unimolecular, and to obey a first-order rate law. In particular, the rate constants for the gas phase decomposition at low pressure of the three α-hydroxycarboxylic acids, glycolic ( I ), lactic ( II ), and 2-hydroxyisobutyric ( III ), to form carbon monoxide, water, and the corresponding carbonyl compound has been determined 3 and expressed as a function of temperature by the following Arrhenius-type equations: …”

Section: Introductionmentioning

confidence: 99%

Theoretical Study of the Gas Phase Decomposition of Glycolic, Lactic, and 2-Hydroxyisobutyric Acids

et al. 1997

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The reaction mechanism associated with the decomposition of three α-hydroxycarboxylic acids (glycolic, lactic, and 2-hydroxyisobutyric) in the gas phase to form carbon monoxide, water, and the corresponding carbonyl compounds has been theoretically characterized by using ab initio analytical gradients at the MP2 level of theory with the 6-31G** and 6-31++G** basis sets. A detailed characterization of the potential energy surface points out the existence of three competitive reaction pathways for the decomposition process. The first pathway describes a two-step mechanism, with water elimination and formation of an α-lactone intermediate, achieved by the nucleophilic attack of the carbonylic oxygen atom of the carboxyl group (mechanism A). The second pathway is also a two-step mechanism, but in this case the formation of the α-lactone is obtained by means of the nucleophilic attack of the hydroxylic oxygen atom of the carboxyl group (mechanism B). These two pathways share a common second step in which the α-lactone decomposes. The third pathway is a one-step process in which the decomposition of the corresponding α-hydroxy acid takes place in a concerted fashion (mechanism C). The geometrical parameters of the stationary points appearing along the three pathways and the components of the transition vectors associated to the transition structures calculated using the 6-31G** basis set are similar to those calculated with the larger 6-31G++G** basis set. The decomposition is favorable along pathway A, and the first step can be considered as the rate-limiting step for the global process. The rate constant values for this step increase in the order of glycolic, lactic, and 2-hydroxyisobutyric acids due to the stabilization of the incipient carbocationic center on C3 with the substitution of hydrogen atoms by methyl groups. The apparent first-order rate constants calculated by transition state theory agree well with the experiments reported by Chuchani and co-workers.

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Several mechanisms in the elimination kinetics of ω‐chlorocarboxylic acids in the gas phase

Cited by 17 publications

References 15 publications

Kinetics of the gas-phase elimination of ?-Bromophenylacetic acid under maximum inhibition

Kinetics of the gas-phase elimination of ?-Bromophenylacetic acid under maximum inhibition

Theoretical Study of the Elimination Kinetics of Carboxylic Acid Derivatives in the Gas Phase. Decomposition of 2-Chloropropionic Acid

Theoretical Study of the Gas Phase Decomposition of Glycolic, Lactic, and 2-Hydroxyisobutyric Acids

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