The elimination kinetics of the title compounds were determined over the temperature range 290.4–420.3°C and pressure range 14.5–44.0 Torr. The reactions, carried out in seasoned vessels and in the presence of the free radical inhibitor toluene, are homogeneous, unimolecular and follow a first‐order rate law. The rate coefficient is expressed by the following Arrhenius equation: for N‐phenylglycine ethyl ester, log [I1 (s−1)]=(12.13±0.38)− (193.6±4.9) kJ mol−1 (2.303 RT)−1; and for N‐phenylglycine, log [k1 (s−1)]=(12.95±0.52)−(177.4±5.8) kJ mol−1 (2.303 RT)−1. Both substrates yield mainly N‐methylaniline and a small amount of aniline. N‐Phenylglycine as a neutral amino acid decomposes 130 times faster than its ethyl ester at 380°C. The mechanisms of these elimination reactions are presented and discussed. Copyright © 2003 John Wiley & Sons, Ltd.

The gas‐phase elimination kinetics of 2,2‐diethoxyethyl amine and 2,2‐diethoxy‐N,N‐diethylethanamine (320–380 °C; 40–150 Torr) in a seasoned reaction vessel are homogeneous, unimolecular and obey a first‐order rate law. These elimination processes involve two parallel reactions. The first gives ethanol and the corresponding 2‐ethoxyethenamine. The latter compound further decomposes to ethylene, CO and the corresponding amine. The second parallel reaction produce ethane and the corresponding ethyl ester of an α‐amino acid. The following Arrhenius expressions are given as:For 2,2‐diethoxyethyl amine For 2,2‐diethoxy‐N,N‐diethylethanamine Comparative kinetic and thermodynamic parameters of the overall, the parallel and the consecutive reactions lead to consider two types of mechanisms in terms of a concerted polar cyclic transition state structures. Copyright © 2008 John Wiley & Sons, Ltd.

The gas‐phase elimination of 1,1‐dimethoxycyclohexane yielded 1‐methoxy‐1‐cyclohexene and methanol. The kinetics were determined in a static system, with the vessels deactivated with allyl bromide, and in the presence of the free radical inhibitor cyclohexene. The working temperature was 310–360 °C and the pressure was 25–85 Torr. The reaction was found to be homogeneous, unimolecular, and follows a first‐order rate law. The temperature dependence of the rate coefficients is given by the following Arrhenius equation: log k(s−1) = [(13.82 ± 0.07) – (193.9 ± 1.0)(kJ mol−1)](2.303RT)−1; r = 0.9995. Theoretical calculations were carried out using density functional theory (DFT) functionals B3LYP, MPW1PW91, and PBE with the basis set 6‐31G(d,p) and 6‐31G++(d,p). The calculated values for the energy of activation and enthalpy of activation are in reasonably good agreement with the experimental values using the PBE/6‐31G (d,p) level of theory. Both experimental results and theoretical calculations suggest a molecular mechanism involving a concerted polar four‐membered cyclic transition state. The transition state structure of methanol elimination from 1,1‐dimethoxycyclohexane is characterized by a significantly elongated CO bond, while the CβH bond is stretched to a smaller extent, as compared to the reactant. The process can be described as moderately asynchronic with some charge separation in the TS. Copyright © 2010 John Wiley & Sons, Ltd.

The gas‐phase elimination kinetics of the title compounds were determined over the temperature range 350–430°C and pressure range 35–240 Torr (1 Torr = 133.3 Pa). The reactions, which were carried out in a static reactor system, seasoned with allyl bromide and in the presence of a free radical inhibitor, are homogeneous, unimolecular and obey a first‐order rate law. The temperature dependences of the overall rate coefficients are given by the following Arrhenius equations: for ethyl oxamate, log [k1 (s−1)] = (13.28 ± 0.20) – (203.7 ± 2.5) kJ mol−1 (2.303RT)−1, for ethyl N,N‐dimethyloxamate, log [k1 (s−1)] = (13.06 ± 0.34) – (206.8 ± 4.4) kJ mol−1(2.303RT)−1, and for ethyl oxanilate, log [k1 (s−1)]= (13.86 ± 0.12)–(207.4 ± 1.5) kJ mol−1(2.303RT)−1. The overall rates, the partial rates and the kinetic and thermodynamic parameters of these eliminations are presented and discussed. These reactions appear to proceed through moderately polar cyclic transition states. Copyright © 2004 John Wiley & Sons, Ltd.

The gas phase thermal decarbonylation of a,b-unsaturated aldehydes E-2-butenal and E-3-phenyl-2-methylpropenal was studied in a static system over the temperature range 380.5-490.0 8C and pressure range 55.5-150 Torr. The reactions are homogeneous and unimolecular and obey a first-order rate law. The rate coefficient is represented by the following Arrhenius equations:EÀ2ÀButenal : log k 1 ðs À1 Þ ¼ ð13:18 AE 0:16Þ À ð212:0 AE 2:0Þ kJ mol À1 ð2:303 RTÞ À1 EÀ3ÀphenylÀ2Àmethylpropenal : log k 1 ðs À1 Þ ¼ ð13:23 AE 0:22Þ À ð234:6 AE 3:2Þ kJ mol À1 ð2:303 RTÞ À1The elimination products of 2-butenal are propene and CO gas, while 3-phenyl-2-methylpropenal produces a-methylstyrene, cis-trans-b-methylstyrene, indan, and CO gas. Kinetic and thermodynamic parameters suggest these elimination reactions to proceed through a three-membered cyclic transition state type of mechanisms. However, a two steps mechanisms for the formation of a carbene type of intermediate through a four-membered cyclic transition structure can not be overlooked.

The gas-phase elimination kinetics of ethyl 2-furoate and 2-ethyl 2-thiophenecarboxylate was carried out in a static reaction system over the temperature range of 623.15-683.15 K (350-410 • C) and pressure range of 30-113 Torr. The reactions proved to be homogeneous, unimolecular, and obey a first-order rate law. The rate coefficients are expressed by the following Arrhenius equations: ethyl 2-furoate, log k 1 (s −1 ) = (11.51 ± 0.17)-(185.6 ± 2.2) kJ mol −1 (2.303 RT) −1 ; ethyl 2-thiophenecarboxylate, log k 1 (s −1 ) = (11.59 ± 0.19)-(183.8 ± 2.4) kJ mol −1 (2.303 RT) −1 . The elimination products are ethylene and the corresponding heteroaromatic 2-carboxylic acid. However, as the reaction temperature increases, the intermediate heteroaromatic carboxylic acid products slowly decarboxylate to give the corresponding heteroaromatic furan and thiophene, respectively. The mechanisms of these reactions are suggested and described.

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 8C 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 logk 1 (s À1 ) ¼ (13.02 AE 0.46) -(161.6 AE 4.7) kJ/mol(2.303 RT) À1 , for tert-butyl N-hydroxycarbamate logk 1 (s À1 ) ¼ (12.52 AE 0.11) -(147.8 AE 1.1) kJ/mol(2.303 RT) À1 , and for 1-(tert-butoxycarbonyl)-imidazole logk 1 (s À1 ) ¼ (11.63 AE 0.21)-(134.9 AE 2.0) kJ/mol(2.303 RT) À1 . 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.

The kinetics of the gas-phase elimination kinetics of CO 2 from furoic acid was determined in a static system over the temperature range 415-455 • C and pressure range 20-50 Torr. The products are furan and carbon dioxide. The reaction, which is carried out in vessels seasoned with allyl bromide and in the presence of the free-radical suppressor toluene and/or propene, is homogeneous, unimolecular, and follows a first-order rate law. The observed rate coefficient is expressed by the following Arrhenius equation: log k 1 (s −1 ) = (13.28 ± 0.16) − (220.5 ± 2.1) kJ mol −1 (2.303 RT) −1 . Theoretical studies carried out at the B3LYP/6-31++G * * computational level suggest two possible mechanisms according to the kinetics and thermodynamic parameters calculated compared with experimental values.