Homogeneous, unimolecular, gas-phase elimination of leaving groups at the alkoyl side of carboxylic acids

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

doi:10.1002/(sici)1099-1395(199606)9:6<348::aid-poc794>3.0.co;2-c

Cited by 9 publications

(11 citation statements)

References 21 publications

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“…1 In the case of decomposition of alkyl chlorides, a syn-elimination with the active participation of a nonbonding pair of the chlorine atom has been considered the driving factor allowing a highly concerted decomposition in the gas-phase. 3,[9][10][11] However, and not free from controversy, mechanisms in the gas phase implying a polar nature of the transition state have been also related to the consideration of very polar intimate ion pair interactions (3), or even semi-ion pair transition structures (4). 1 Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

“…[3][4][5][6][7][8] Extensive work, both experimental 2, 4, 9-10 and theoretically oriented 3,[9][10][11] have pointed out to the polarization of the ‫ܥ‬ ఋା ••• ܺ ఋି bond as the key chemical event associated to the rate determining step of the dehydrohalogenation process (See Scheme 1). 3,[8][9][10][11][12][13][14][15][16][17][18] The intimate nature of the electronic rearrangement driving this type of transformations remains certainly unknown. Thermal decomposition of alkyl chlorides in the gas phase via a four-membered planar transition structure (TS), including polar (1), concerted (2), ion pair (3) or semi ion pair alternatives (4).…”

Section: Introductionmentioning

confidence: 99%

“…1 In the case of decomposition of alkyl chlorides, a syn-elimination with the active participation of a nonbonding pair of the chlorine atom has been considered the driving factor allowing a highly concerted decomposition in the gas-phase. [3][4][5][6][7][8] Extensive work, both experimental 2,4,9,10 and theoretically oriented 3,[9][10][11] have pointed out to the polarization of the C d+ /X dÀ bond as the key chemical event associated to the rate determining step of the dehydrohalogenation process (see Scheme 1). 1 The catalytic substituent effects on the rates, 2,4,9,10 including both inductive and resonance effects on the centers C a and C b , have been rationalized on the basis of favouring a heterolytic transition structure (1) or a completely concerted alternative (2).…”

Section: Introductionmentioning

confidence: 99%

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Understanding the thermal dehydrochlorination reaction of 1-chlorohexane. Revealing the driving bonding pattern at the planar catalytic reaction center

et al. 2015

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The nature of bonding along the gas-phase thermal decomposition of 1-chlorohexane to produce 1-hexene and hydrogen chloride has been examined at the DFT M05-2X/6-311+G(d,p) level of theory. Based on results both from energetical and topological analysis of the electron localization function (ELF), we propose to rationalize the experimental available results not in terms of a decomposition via a four-membered cyclic transition structure (TS), but properly as a two stage one step reaction mechanism featuring a slightly asynchronous process associated to the catalytic planar reaction center at the TS. In this context, the first electronic stage corresponds to the ‫ܥ‬ ఋା ••• ‫݈ܥ‬ ఋି bond cleavage, which take place on the activation path earlier the transition structure be reached. There is no evidence of a Cl-C bond at the TS configuration. The second stage, associated to the top of the energy barrier, includes the TS and extends beyond on the deactivation pathway towards the products. The existence of both bonding and nonbonding non covalent interactions (NCI) are also revealed for the first time for the TS configuration. 17 47 to point -9 along the IRC reaction pathway. Arbitrarily the second stage concerning main electronic changes will be associated to points -9 to +9. Both stages refer to regions where key electronic changes driving the transformation take place. Note that from point -34 to point -5, the population associated to the disynaptic basin V(C α ,C β ) increases from 1.99e to 2.20e, whereas the population integrated in the disynaptic protonated basin V(H β ,C β ) decreases from 1.98e to 1.72e. The attractor corresponding to the forming double bond localizes out of the line connecting the carbon center cores. This topology for the C  -C  region remains unchanged until point 12 in region g. At the top of the energy barrier, within the entire interval IRC=(-0.97962,+0.97971), i.e., point -9 to point 9, we observe an isolated electron localization region integrating to 7.64e which is associated to the migrating chlorine center. This picture, on the top of the barrier, corresponds to a lonely chlorine atom bearing an electronic charge of -0.64 while evolving to the encounter of the H β center.Thereafter, within the tiny region d four valence monosynaptic basins V(Cl) associated to the negatively charged chlorine center adopt a tetrahedral conformation, with an increasing in the population from 7.64e to 7.70e. In this region the valence basins populations for V(C α ,C β ) and V(H β ,C β ) varies from 2.41e to 2.34e, and from 1.81e to 1.51e, respectively. The migrating chlorine center develops thus a maximum charge of -0.71 at the transition structure (point 0). ELF picture of bonding reveals that activation events are mainly associated to conformational changes in preparation of the reaction center (region a), followed by the breaking of the Cl-C α bond (regions b and c), and the start of the migration of H  atom with the associated bonding changes at C α -C β -H β moiety (regions c and d). Regarding t...

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“…1 In the case of decomposition of alkyl chlorides, a syn-elimination with the active participation of a nonbonding pair of the chlorine atom has been considered the driving factor allowing a highly concerted decomposition in the gas-phase. 3,[9][10][11] However, and not free from controversy, mechanisms in the gas phase implying a polar nature of the transition state have been also related to the consideration of very polar intimate ion pair interactions (3), or even semi-ion pair transition structures (4). 1 Scheme 1.…”

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…1 In the case of decomposition of alkyl chlorides, a syn-elimination with the active participation of a nonbonding pair of the chlorine atom has been considered the driving factor allowing a highly concerted decomposition in the gas-phase. [3][4][5][6][7][8] Extensive work, both experimental 2,4,9,10 and theoretically oriented 3,[9][10][11] have pointed out to the polarization of the C d+ /X dÀ bond as the key chemical event associated to the rate determining step of the dehydrohalogenation process (see Scheme 1). 1 The catalytic substituent effects on the rates, 2,4,9,10 including both inductive and resonance effects on the centers C a and C b , have been rationalized on the basis of favouring a heterolytic transition structure (1) or a completely concerted alternative (2).…”

Section: Introductionmentioning

confidence: 99%

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Understanding the thermal dehydrochlorination reaction of 1-chlorohexane. Revealing the driving bonding pattern at the planar catalytic reaction center

et al. 2015

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“…As reported in previous work 14 and with the kinetic parameters given in Table 9, the order of leaving ability of substituents at the 2-position of carboxylic acids where their displacements are favoured by the acidic H of the COOH is as follows:…”

Section: Methyl 2-acetoxypropionatementioning

confidence: 55%

Kinetics and mechanism of the gas-phase elimination of primary, secondary and tertiary 2-acetoxycarboxylic acids

Chuchani¹,

Domínguez²,

Herize³

et al. 2000

J. Phys. Org. Chem.

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The gas‐phase elimination kinetics of the title compounds were examined over the temperature range 220.1 –349.0 °C and pressure range 19–120 Torr. These reactions proved to be homogeneous and unimolecular and to follow a first‐order rate law. The overall rate coefficients are expressed by the following Arrhenius equations: for 2‐acetoxyacetic acid, logk1 (s−1) = (12.03 ± 0.28) − (170.8 ± 3.2) kJ mol−1 (2.303RT)−1; for 2‐acetoxypropionic acid, logk1 (s−1) = (13.16 ± 0.24) − (174.2 ± 2.6) kJ mol−1 (2.303RT)−1 ; for 2‐acetoxy‐2‐methylpropionic acid, logk1 (s−1) = (13.40 ± 0.72) − (160.9 ± 5.03) kJ mol−1 (2.303RT)−1. The products of the acetoxyacids are acetic acid, the corresponding carbonyl compound and CO gas, except for 2‐acetoxy‐2‐methylpropionic acid, which undergoes a parallel elimination to give methacryclic acid and acetic acid. The rates of elimination are found to increase from primary to tertiary carbon bearing the acetoxy group. The mechanism appears to proceed through a discrete polar five‐membered cyclic transition state, where the acidic hydrogen of the COOH assists the leaving acetoxy group, followed by the participation of the carbonyl oxygen for α‐lactone formation. The unstable α‐lactone intermediate decomposes rapidly into the corresponding carbonyl compound and CO gas. The importance of the acidic H of the COOH assistance in the acetoxy acid mechanisms may be revealed in the elimination kinetics of methyl 2‐acetoxypropionate. This substrate was studied in the ranges 370.0 –430.0 °C and 36–125 Torr. This reaction is homogeneous, unimolecular and follows a first‐order rate law. The products are methyl acrylate and acetic acid. The rate coefficients is given by the equation logk1 (s−1) = (12.63 ± 0.35) − (201.7 ± 4.4) kJ mol−1 (2.303RT)−1. Copyright © 2000 John Wiley & Sons, Ltd.

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“…Several mechanisms of the nucleophilic halogen substitution are feasible. Chuchani et al23, 24 dealing with the investigation of the gas phase elimination of hydrogen halides from halocarboxylic acid suggested a mechanism of anchimeric interaction of the leaving chlorine atom with the acidic hydrogen of the carboxyl group with the subsequent formation of propiolactone, or an alternative mechanism involving a four‐membered cyclic transition state (Scheme ).…”

Section: Resultsmentioning

confidence: 99%

N‐alkylation of chitosan by β‐halopropionic acids in the presence of various acceptors

Пестов

Skorik

Kogan

et al. 2007

J of Applied Polymer Sci

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N-carboxyethylation of chitosan by b-halopropionic acids in the presence of various proton and halogen ion acceptors was investigated. It has been observed that carboxyethylation of chitosan in aqueous medium is accompanied by the by-processes of hydrolysis and dehydrohalogenation of the b-halopropionic acids yielding b-hydroxypropionic acid, bis(2-carboxyethyl) ether, and acrylic acid. Degree of carboxyethyl substitution (DS) of chitosan and the relative rates of the by-processes varied significantly depending on the conditions used and nature of the proton or halogen ion acceptor. At carboxyethylation of chitosan with the alkaline b-bromopropionates, the DS increased in the order Cs , Ba 2þ ), the highest DS was obtained with strontium and barium salts, which could be subsequently removed from the reaction mixture by precipitation as sulfates. Among the organic bases applied (tetrabutylammonium hydroxide, triethylamine, trimethylamine, pyridine, 4-N,N-dimethylaminopyridine, 2,6-lutidine, and 1,5-diazabicyclo[4.3.0] non-5-ene), the highest DS was obtained using a moderately strong base triethylamine. For the halogen acceptors (Pb 2þ , Ag þ , Tl þ ), the stoichiometrically highest DS was achieved in a system comprising iodopropionic acid plus Tl þ and a comparable conversion rate was obtained using also a combination of chloropropionic acid and Ag þ . A novel alternative preparative approach-gel-state synthesis-was suggested that provides for the highest DS at the optimum reaction conditions.

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Homogeneous, unimolecular, gas-phase elimination of leaving groups at the alkoyl side of carboxylic acids

Cited by 9 publications

References 21 publications

Understanding the thermal dehydrochlorination reaction of 1-chlorohexane. Revealing the driving bonding pattern at the planar catalytic reaction center

Understanding the thermal dehydrochlorination reaction of 1-chlorohexane. Revealing the driving bonding pattern at the planar catalytic reaction center

Kinetics and mechanism of the gas-phase elimination of primary, secondary and tertiary 2-acetoxycarboxylic acids

N‐alkylation of chitosan by β‐halopropionic acids in the presence of various acceptors

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