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First-order Rate Law (first-order + rate_law)
Selected AbstractsHomogeneous, unimolecular gas-phase elimination kinetics of ethyl esters of glyoxylic, 2-oxo-propanoic, and 3-methyl-2-oxo-butanoic acidsINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 5 2007Andreina Reyes The rates of elimination of several ethyl esters of 2-oxo-carboxylic acid were determined in a seasoned static reaction vessel over the temperature range 350,430°C and pressure range 33,240 Torr. The reactions, in the presence of a free-radical inhibitor, are homogeneous, unimolecular, and follow a first-order rate law. The overall and partial rate coefficients are expressed by the Arrhenius equation. Ethyl glyoxalate Ethyl 2-oxo-propionate Ethyl 3-methyl-2-oxo-butyrate The mechanisms of these elimination reactions are described in terms of concerted cyclic transition state structures. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 268,275, 2007 [source] The unimolecular elimination kinetics of benzaldoxime in the gas phaseINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 3 2007Libia L. Julio The kinetics of the gas-phase elimination of benzaldoxime was determined in a static reaction system over the temperature and pressure range 350°C,400°C and 56,140 Torr, respectively. The products obtained were benzonitrile and water. The reaction was found to be homogeneous, unimolecular, and tend to obey a first-order rate law. The observed rate coefficient is represented by the following Arrhenius equation: According to kinetic and thermodynamic parameters, the reaction proceeds through a concerted, semi-polar, four-membered cyclic transition state type of mechanism. © 2007 Wiley Periodicals, Inc. 39: 145,147, 2007 [source] The elimination kinetics and mechanisms of ethyl piperidine-3-carboxylate, ethyl 1-methylpiperidine-3-carboxylate, and ethyl 3-(piperidin-1-yl)propionate in the gas phaseINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 2 2006Angiebelk Monsalve The gas-phase elimination kinetics of the above-mentioned compounds were determined in a static reaction system over the temperature range of 369,450.3°C and pressure range of 29,103.5 Torr. The reactions are homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are given by the following Arrhenius expressions: ethyl 3-(piperidin-1-yl) propionate, log k1(s,1) = (12.79 ± 0.16) , (199.7 ± 2.0) kJ mol,1 (2.303 RT),1; ethyl 1-methylpiperidine-3-carboxylate, log k1(s,1) = (13.07 ± 0.12),(212.8 ± 1.6) kJ mol,1 (2.303 RT),1; ethyl piperidine-3-carboxylate, log k1(s,1) = (13.12 ± 0.13) , (210.4 ± 1.7) kJ mol,1 (2.303 RT),1; and 3-piperidine carboxylic acid, log k1(s,1) = (14.24 ± 0.17) , (234.4 ± 2.2) kJ mol,1 (2.303 RT),1. The first step of decomposition of these esters is the formation of the corresponding carboxylic acids and ethylene through a concerted six-membered cyclic transition state type of mechanism. The intermediate ,-amino acids decarboxylate as the ,-amino acids but in terms of a semipolar six-membered cyclic transition state mechanism. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 106,114, 2006 [source] The mechanism of neutral amino acid decomposition in the gas phase.INTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 8 2001N -dimethylglycine, N -dimethylglycine ethyl ester, The elimination kinetics of N, ethyl 1-piperidineacetate The gas-phase elimination kinetics of the ethyl ester of two ,-amino acid type of molecules have been determined over the temperature range of 360,430°C and pressure range of 26,86 Torr. The reactions, in a static reaction system, are homogeneous and unimolecular and obey a first-order rate law. The rate coefficients are given by the following equations. For N,N-dimethylglycine ethyl ester: log k1(s,1) = (13.01 ± 3.70) , (202.3 ± 0.3)kJ mol,1 (2.303 RT),1 For ethyl 1-piperidineacetate: log k1(s,1) = (12.91 ± 0.31) , (204.4 ± 0.1)kJ mol,1 (2.303 RT),1 The decompositon of these esters leads to the formation of the corresponding ,-amino acid type of compound and ethylene. However, the amino acid intermediate, under the condition of the experiments, undergoes an extremely rapid decarboxylation process. Attempts to pyrolyze pure N,N-dimethylglycine, which is the intermediate of dimethylglycine ethyl ester pyrolysis, was possible at only two temperatures, 300 and 310°C. The products are trimethylamine and CO2. Assuming log A = 13.0 for a five-centered cyclic transition-state type of mechanism in gas-phase reactions, it gives the following expression: log k1(s,1) = (13.0) , (176.6)kJ mol,1 (2.303 RT),1. The mechanism of these ,-amino acids differs from the decarbonylation elimination of 2-substituted halo, hydroxy, alkoxy, phenoxy, and acetoxy carboxylic acids in the gas phase. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33:465,471, 2001 [source] Joint theoretical and experimental study of the gas-phase elimination kinetics of tert -butyl ester of carbamic, N, N -dimethylcarbamic, N -hydroxycarbamic acids and 1-(tert -butoxycarbonyl)-imidazoleJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2007Jose R Mora Abstract The gas-phase elimination kinetics of the title compounds were carried out in a static reaction system and seasoned with allyl bromide. The working temperature and pressure ranges were 200,280,°C and 22,201.5,Torr, respectively. The reactions are homogeneous, unimolecular, and follow a first-order rate law. These substrates produce isobutene and corresponding carbamic acid in the rate-determining step. The unstable carbamic acid intermediate rapidly decarboxylates through a four-membered cyclic transition state (TS) to give the corresponding organic nitrogen compound. The temperature dependence of the rate coefficients is expressed by the following Arrhenius equations: for tert -butyl carbamate logk1 (s,1),=,(13.02,±,0.46),,,(161.6,±,4.7) kJ/mol(2.303,RT),1, for tert -butyl N -hydroxycarbamate logk1 (s,1),=,(12.52,±,0.11),,,(147.8,±,1.1) kJ/mol(2.303,RT),1, and for 1-(tert -butoxycarbonyl)-imidazole logk1 (s,1),= (11.63,±,0.21),(134.9,±,2.0) kJ/mol(2.303,RT),1. Theoretical studies of these elimination were performed at Møller,Plesset MP2/6-31G and DFT B3LYP/6-31G(d), B3LYP/6-31G(d,p) levels of theory. The calculated bond orders, NBO charges, and synchronicity (Sy) indicate that these reactions are concerted, slightly asynchronous, and proceed through a six-membered cyclic TS type. Results for estimated kinetic and thermodynamic parameters are discussed in terms of the proposed reaction mechanism and TS structure. Copyright © 2007 John Wiley & Sons, Ltd. [source] Experimental and theoretical studies of the elimination kinetics of 3-hydroxy-3-methyl-2-butanone in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7 2005Mariana Graterol Abstract The kinetics of the gas-phase elimination of 3-hydroxy-3-methyl-2-butanone was investigated in a static system, seasoned with allyl bromide, and in the presence of the free chain radical inhibitor toluene. The working temperature and pressure range were 439.6,489.3°C and 81,201.5,Torr (1,Torr,=,133.3,Pa), respectively. The reaction was found to be homogeneous, unimolecular and to follow a first-order rate law. The products of elimination are acetone and acetaldehyde. The temperature dependence of the rate coefficients is expressed by the following equation: log[k1(s,1)],=,(13.05±0.53),(229.7±5.3),kJ,mol,1 (2.303RT),1. Theoretical estimations of the mechanism of this elimination suggest a molecular mechanism of a concerted non-synchronous four-membered cyclic transition-state process. An analysis of bond order and natural bond orbital charges suggests that the bond polarization of C(OH),C(O),, in the sense of C(OH),+&·C(O),,, is rate limiting in the elimination reaction. The rate coefficients obtained experimentally are in reasonably good agreement with the theoretical calculations. The mechanism of 3-hydroxy-3-methyl-2-butanone elimination is described. Copyright © 2005 John Wiley & Sons, Ltd. [source] Mechanism and structure,reactivity correlation in the homogeneous, unimolecular elimination kinetics of 2-substituted ethyl methylcarbonates in the gas phaseJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 11 2003Gabriel Chuchani Abstract The gas-phase elimination kinetics of 2-substituted ethyl methylcarbonates were determined in a static reaction system over the temperature range of 323,435°C and pressure range 28.5,242 Torr. The reactions are homogeneous, unimolecular and follow a first-order rate law. The kinetic and thermodynamic parameters are reported. The 2-substituents of the ethyl methylcarbonate (CH3OCOOCH2CH2Z, Z=substituent) give an approximate linear correlation when using the Taft,Topsom method, log(kZ/kH)=,(0.57±0.19),,+(1.34±0.49),R, (r=0.9256; SD=0.16) at 400°C. This result implies the elimination process to be sensitive to steric factors, while the electronic effect is unimportant. However, the resonance factor has the greatest influence for a favorable abstraction of the ,-hydrogen of the C,,H bond by the oxygen carbonyl. Because ,, is significant, a good correlation of the alkyl substituents of carbonates with Hancock's steric parameters was obtained: log(kR/kH) versus ESC for CH3OCOOCH2CH2R at 400°C, R=alkyl, ,=,0.17 (r=0.9993, SD=0.01). An approximate straight line was obtained on plotting these data with the reported Hancock's correlation of 2-alkyl ethylacetates. This result leads to evidence for the ,-hydrogen abstraction by the oxygen carbonyl and not by the alkoxy oxygen at the opposite side of the carbonate. The carbonate decompostion is best described in terms of a concerted six-membered cyclic transition state type of mechanism. Copyright © 2003 John Wiley & Sons, Ltd. [source] Kinetics of elimination of several heterocyclic carbamates in the gas phase,JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2002Yannely Brusco Abstract The kinetics of the gas-phase elimination of several heterocyclic carbamates were determined in a static system over the temperature range 190.0,409.7,°C and the pressure range 26.5,125,Torr (1,Torr,=,133.3,Pa). The reactions in seasoned vessels, with the free radical inhibitor cyclohexene and/or toluene always present, are homogeneous and unimolecular and obey a first-order rate law. The observed rate coefficients are represented by the following Arrhenius equations: for tert -butyl-1-pyrrolidine carboxylate, log k1 (s,1),=,(11.36,±,0.31) ,(145.4,±,3.1)kJ,mol,1 (2.303RT),1; for 1-(tert -butoxycarbonyl)-2-pyrrolidinone, log k1 (s,1),=,(11.54,±,0.29) ,(140.8,±,2.8)kJ,mol,1 (2.303RT),1; for tert -butyl-1-pyrrole carboxylate, log k1 (s,1),=,(12.12,±,0.05) ,(145.2,±,1.0),kJ,mol,1 (2.303RT),1; and for 1-ethylpiperazine carboxylate, log k1 (s,1),=,(12.05,±,0.19) ,(188.2,±,4.6),kJ,mol,1 (2.303RT),1. The saturated heterocyclic carbamates show a decrease in rates of elimination due to electronic factors. Heterocyclic carbamates with a nitrogen atom able to delocalize its electrons with ,-bonds present in the ring were found to enhance the rates due to resonance interactions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Mechanistic Investigation of the Oxygen-Atom-Transfer Reactivity of Dioxo-molybdenum(VI) ComplexesCHEMISTRY - A EUROPEAN JOURNAL, Issue 28 2006Brian W. Kail Abstract The oxygen-atom-transfer (OAT) reactivity of [LiPrMoO2(OPh)] (1, LiPr=hydrotris(3-isopropylpyrazol-1-yl)borate) with the tertiary phosphines PEt3 and PPh2Me in acetonitrile was investigated. The first step, [LiPrMoO2(OPh)]+PR3,[LiPrMoO(OPh)(OPR3)], follows a second-order rate law with an associative transition state (PEt3, ,H,,=48.4 (±1.9) kJ,mol,1, ,S,,=,149.2 (±6.4) J,mol,1,K,1, ,G,,=92.9 kJ,mol,1; PPh2Me, ,H,,=73.4 (±3.7) kJ,mol,1, ,S,,=,71.9 (±2.3) J,mol,1,K,1, ,G,,=94.8 kJ,mol,1). With PMe3 as a model substrate, the geometry and the free energy of the transition state (TS) for the formation of the phosphine oxide-coordinated intermediate were calculated. The latter, 95 kJ,mol,1, is in good agreement with the experimental values. An unexpectedly large O-P-C angle calculated for the TS suggests that there is significant O-nucleophilic attack on the PC ,* in addition to the expected nucleophilic attack of the P on the MoO ,*. The second step of the reaction, that is, the exchange of the coordinated phosphine oxide with acetonitrile, [LiPrMoO(OPh)(OPR3)] + MeCN , [LiPrMoO(OPh)(MeCN)] + OPR3, follows a first-order rate law in MeCN. A dissociative interchange (Id) mechanism, with activation parameters of ,H,,=93.5 (±0.9) kJ,mol,1, ,S,,=18.2 (±3.3) J,mol,1,K,1, ,G,,=88.1 kJ,mol,1 and ,H,,=97.9 (±3.4) kJ,mol,1, ,S,,=47.3 (±11.8) J,mol,1,K,1, ,G,,=83.8 kJ,mol,1, for [LiPrMoO(OPh)(OPEt3)] (2,a) and [LiPrMoO(OPh)(OPPh2Me)] (2,b), respectively, is consistent with the experimental data. Although gas-phase calculations indicate that the MoOPMe3 bond is stronger than the MoNCMe bond, solvation provides the driving force for the release of the phosphine oxide and formation of [LiPrMoO(OPh)(MeCN)] (3). [source] | ||||||||||