The gas-phase thermal decomposition of cyclobutanol

1982 ◽  
Vol 60 (20) ◽  
pp. 2537-2541 ◽  
Author(s):  
R. A. Back
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Hydrogen Transfer ◽  
Frequency Factor ◽  
Static System ◽  
Cyclic Transition ◽  
Surface Catalysis ◽  
Cyclic Transition State ◽  
Strong Surface ◽  
A Minor

The thermal decomposition of cyclobutanol has been studied in the gas phase in a static system at pressures from 3–6 Torr and temperatures from 250 to 450 °C. The major products observed were ethylene and acetaldehyde, while n-butyraldehyde was a minor product. First-order rate constants based on ethylene formation in a Pyrex vessel conditioned by carbon deposition gave Arrhenius parameters of A = 2.14 (± 0.2) × 1014 s−l and E = 57.3 (± 1) kcal/mol. Under the same conditions, the ratio n-butyraldehyde/ethylene increased with decreasing temperature, corresponding to an activation energy of about 50 kcal/mol for butyraldehyde formation and a frequency factor about 104 times lower than that for ethylene production. In an untreated Pyrex vessel the decomposition showed strong surface catalysis with much lower activation energies for both processes. It is suggested that both ethylene and n-butyraldehyde are formed from a common ĊH2CH2CH2ĊHOH biradical by cleavage and by hydrogen transfer through a 6-membered cyclic transition state respectively. The thermal decomposition is thus the reverse of the Type II and II′ processes observed in the photolysis of n-butyraldehyde.

The gas-phase photochemistry and thermal decomposition of glyoxylic acid

1985 ◽  
Vol 63 (2) ◽  
pp. 542-548 ◽  
Author(s):  
R. A. Back ◽  
S. Yamamoto
Keyword(s):  
Thermal Decomposition ◽  
Carbon Monoxide ◽  
Absorption Spectrum ◽  
Gas Phase ◽  
Singlet State ◽  
Glyoxylic Acid ◽  
Static System ◽  
First Order ◽  
Increasing Temperature ◽  
Homogeneous Formation

The photolysis of glyoxylic acid vapour has been studied at five wavelengths, 382, 366, 346, 275, and 239 nm, and pressures from about 1 to 6 Torr, at a temperature of 355 K. Major products were CO2 and CH2O, initially formed in almost equal amounts, while minor products were CO and H2. Except at 382 nm, the system was complicated by the rapid secondary photolysis of CH2O. Three primary processes are suggested, each involving internal H-atom transfer followed by dissociation.The absorption spectrum is reported and shows the three distinct absorption systems. A finely-structured spectrum from about 320 to 400 nm is attributed to a transition to the first excited π* ← n+ singlet state; a more diffuse absorption ranging from about 290 nm to a maximum at 239 nm is assigned to the π* ← n− state, while a much stronger absorption beginning below 230 nm is attributed to the π* ← π transition. Product ratios vary with wavelength and depend on which excited state is involved.The thermal decomposition was studied briefly in a static system at temperatures from 470 to 710 K and pressures from 0.4 to 8 Torr. Major products were again CO2 and CH2O, but the latter was always less than stoichiometric. First-order rate constants for the apparently homogeneous formation of CO2 are described by Arrhenius parameters log A (s−1) = 7.80 and E = 30.8 kcal/mol. Carbon monoxide and H2 were minor products, and the CO/CO2 ratio increased with increasing temperature and showed some surface enhancement at lower temperatures. The SF6-sensitized thermal decomposition of glyoxylic acid, induced by a pulsed CO2 laser, was briefly studied, with temperatures estimated to be in the 1100–1600 K range, and the CO/CO2 ratio increased with increasing temperature, continuing the trend observed in the static system.

Chemistry of Polynuclear Compounds. IV. The Reduction of Polynuclear Quinones with cyclohexyl-p-toluene Sulphonate

1960 ◽  
Vol 13 (1) ◽  
pp. 103 ◽  
Author(s):  
W Kelly ◽  
JS Shannon
Keyword(s):  
Transition State ◽  
Hydrogen Transfer ◽  
Alternative Methods ◽  
Cyclic Transition ◽  
Polynuclear Compounds ◽  
Cyclic Transition State

In an investigation into the coking mechanism of coal, polynuclear quinones have been adopted as models. Using cyclohexyl-p-toluene sulphonate the following quinones have been reduced to their parent hydrocarbons : dibenzanthrone, isodibenzanthrone, pyranthrone, 4,10-dibromoanthanthrone, anthraquinone (and anthrone), 1,5-dimethoxyanthraquinone, and 1,8-dimethoxyanthraquinone. The reaction gave favourable yields compared with alternative methods, but had the advantage that substituent groups such as halogen and alkoxyl were unattacked. A mechanism is proposed involving complexing of cyclohexyl cations with the quinones, followed by hydrogen-transfer via a resonance-stabilized cyclic transition state.

scholarly journals Quantum-chemical study of mechanisms of benzamide and benzenesulfonamide reactions with 3-nitrobenzenesulfonic acid chloride in the gas phase

2020 ◽  
Vol 63 (8) ◽  
pp. 86-93
Author(s):  
Ludmila B. Kochetova ◽  
◽  
Tatyana P. Kustova ◽  
Al’ona A. Kruglyakova ◽  
◽  
...  
Keyword(s):  
Transition State ◽  
Gas Phase ◽  
Acid Chloride ◽  
Quantum Chemical ◽  
Acid Amide ◽  
Quantum Chemical Study ◽  
Nucleophilic Attack ◽  
Cyclic Transition ◽  
Significant Difference ◽  
Cyclic Transition State

Quantum-chemical simulation of mechanisms of 3-nitrobenzenesulfonic acid chloride interactions with benzoic and benzenesulfonic acids amides in the gas phase was carried out by calculating the three-dimensional potential energy surfaces of these reactions (DFT//B3LYP/6-311G(d,p) level). It was found that in both of the processes considered, a single route can be realized containing a single saddle point and starting as an axial attack of the nucleophile. Further approach of the reagent molecules proceeds with a decrease in the angle of nucleophilic attack to ≈ 130o in the reaction transition state and ≈ 100o – in the reaction product – sulfonamide. It was shown that the studied reactions proceed according to the bimolecular concerted mechanism of nucleophilic substitution SN2, which implies the formation of a single transition state along the reaction pathway. It was found that the geometric structure of the reaction centers in the transition states of the processes is intermediate between the trigonal bipyramid and the tetragonal pyramid, which is explained by the change in the angle of nucleophilic attack when the reagent molecules approach each other. It was found that in benzamide sulfonylation reaction, a cyclic transition state is formed, in which the forming and loosening bonds lie in the same plane, and the H-Cl distance corresponds to the length of the hydrogen bond. In benzenesulfonamide reaction with 3-nitrobenzenesulfonyl chloride, the transition state is not cyclic. The activation energies of the reactions are calculated; they were 155 kJ/mol in the benzamide sulfonylation reaction and 150 kJ/mol in the process with the participation of benzenesulfonic acid amide. The closeness of the obtained values is associated with the similar structure of the amide and sulfamide groups containing electrophilic centers near the amino groups. A significant difference in the rate constants of the studied reactions, which was found earlier, when they occur in aqueous dioxane, is explained by the features of –CONH2 and –SO2NH2 groups specific solvation and the contribution of the entropy factor to the reaction rate: the cyclic transition state of the benzamide reaction with 3-nitrobenzenesulfonyl chloride is more ordered in comparison with a non-cyclic transition state of the reaction with benzenesulfonamide participation, which can promote faster occurence of the first process.

Kinetics and mechanism of the thermal decomposition of N-nitrosodiphenylmethylimine

1981 ◽  
Vol 59 (3) ◽  
pp. 559-562 ◽  
Author(s):  
Michael T.H. Liu ◽  
Toshikazu Ibata
Keyword(s):  
Thermal Decomposition ◽  
Transition State ◽  
Experimental Evidence ◽  
Kinetics And Mechanism ◽  
Ring Closure ◽  
Decomposition Products ◽  
Cyclic Transition ◽  
First Order ◽  
Closure Mechanism ◽  
Cyclic Transition State

The thermal decomposition of N-nitrosodiphenylmethylimine has been investigated in various solvents. The decomposition products are benzophenone and nitrogen. The ΔH†and ΔS† parameters for these first-order decompositions have been determined. The experimental evidence is consistent with the hypothesis that the thermolysis of N-nitrosodiphenylmethylimine involves the formation of a cyclic transition state via an electrocyclic ring closure mechanism.

Electrostatic effects on ionization equilibria: An MNDO study of proton and hydrogen transfer reactions of 4-fluorobutylamine

1990 ◽  
Vol 55 (1) ◽  
pp. 1-9 ◽  
Author(s):  
Zdeněk Friedl ◽  
Stanislav Böhm
Keyword(s):  
Hydrogen Transfer ◽  
Substituent Effects ◽  
Radical Cations ◽  
Transfer Reactions ◽  
Protonated Forms ◽  
Minor Part ◽  
Bond Strengths ◽  
Ionization Equilibria ◽  
A Minor ◽  
Gas Phase Basicities

The relative enthalpies of proton transfer δ ΔH0and homolytic bond strengths δDH0(B-H+) were calculated by the MNDO method for the sp and ap conformers of 4-flurobutylamine. The data obtained, along with the experimental gas phase basicities, are compared with the values predicted by the electrostatic theory. It is shown that the substituent polar effects FD on the basicities of amines are predominantly due to interactions in their protonated forms (X-B-H+) and/or radical-cations (X-B+.), those in the neutral species (X-B) playing a minor part. A contribution, which is considerably more significant in the sp conformer than in the ap conformer, arises probably also from substituent effects on the homolytic bond strength DH0(B-H+.

Kinetic Studies of [4n+2]π-Thermal Cyclodimerization of 1-(3-Pyridazinyl)-3-oxidopyridinium Betaines

1992 ◽  
Vol 57 (9) ◽  
pp. 1951-1959 ◽  
Author(s):  
Madlene L. Iskander ◽  
Samia A. El-Abbady ◽  
Alyaa A. Shalaby ◽  
Ahmed H. Moustafa
Keyword(s):  
Energy Gap ◽  
Activation Parameters ◽  
Kinetic Studies ◽  
Cyclic Transition ◽  
Concerted Mechanism ◽  
First Order ◽  
Thermodynamic Activation Parameters ◽  
Cyclic Transition State ◽  
Complete Dissociation ◽  
Homo Lumo

The reactivity of the base induced cyclodimerization of 1-(6-arylpyridazin-3-yl)-3-oxidopyridinium chlorides in a pericyclic process have been investigated kinetically at λ 380 nm. The reaction was found to be second order with respect to the liberated betaine and zero order with respect to the base. On the other hand dedimerization (monomer formation) was found to be first order. It was shown that dimerization is favoured at low temperature, whereas dedimerization process is favoured at relatively high temperature (ca 70 °C). Solvent effects on the reaction rate have been found to follow the order ethanol > chloroform ≈ 1,2-dichloroethane. Complete dissociation was accomplished only in 1,2-dichloroethane at ca 70 °C. The thermodynamic activation parameters have been calculated by a standard method. Thus, ∆G# has been found to be independent on substituents and solvents. The high negative values of ∆S# supports the cyclic transition state which is in favour with the concerted mechanism. MO calculations using SCF-PPP approximation method indicated low HOMO-LUMO energy gap of the investigated betaines.

DECOMPOSITION PRESSURES OF FERRIC SULPHATE AND ALUMINUM SULPHATE

1960 ◽  
Vol 38 (11) ◽  
pp. 2196-2202 ◽  
Author(s):  
N. A. Warner ◽  
T. R. Ingraham
Keyword(s):  
Gas Phase ◽  
Static System ◽  
Ferric Sulphate ◽  
Kcal Mole ◽  
Aluminum Sulphate ◽  
Temperature And Pressure ◽  
Pressure Changes ◽  
Mercury Manometer ◽  
Decomposition Pressure ◽  
Gas Pressures

The gas pressures over samples of anhydrous ferric sulphate and anhydrous aluminum sulphate have been measured in a static system, using a mercury manometer in which the exposed surface was covered with a flexible Pyrex bellows. The calculated ΔH for the decomposition of Fe2(SO4)3 was +135.4 kcal/mole. It was not possible to calculate the ΔH for the Al2(SO4)3 decomposition, because a discrete aluminum oxide with singular thermodynamic properties was not obtained.In the Fe2(SO4)3 system, the fraction of SO3 in the gas phase was found to be almost constant over the range of temperature and pressure changes used in the study.At any given temperature, the decomposition pressure over a ferric sulphate sample is greater than that over an aluminum sulphate sample, thus indicating that preferential decomposition of ferric sulphate should be thermodynamically feasible in mixtures of ferric sulphate and aluminum sulphate.

Synthesis of Sic Fine Particles by Gas-Phase Reaction Under Short-Time Microgravity

1992 ◽  
Vol 286 ◽  
Author(s):  
Takeshi Okutani ◽  
Yoshinori Nakata ◽  
Masaakt Suzuki ◽  
Yves Maniette ◽  
Nobuyoshi Goto ◽  
...  
Keyword(s):  
Thermal Decomposition ◽  
Heat Source ◽  
Size Distribution ◽  
Gas Phase ◽  
Fine Particles ◽  
Rapid Heating ◽  
Exothermic Reaction ◽  
Phase Reaction ◽  
Gas Phase Reaction ◽  
Short Time

ABSTRACTSiC fine particles were synthesized by the gas-phase thermal decomposition of tetramethylsilane (Si(CH3)4) in hydrogen under microgravity of 10−4G for 10 sec. Rapid heating to the temperature over 800°C which is required for thermal decomposition of Si(CH3)4) under short-time microgravity was attained using a chemical oven where the heat of exothermic reaction of combustion synthesis of Ti-A1-4B composites was used as the heat source. Monodisperse and spherical SiC fine particles were synthesized under microgravity, whereas aggregates of SiC fine particles were synthesized under 1 G gravity. The SiC particles synthesized under microgravity (150-200 nm) were bigger in size and narrower in size distribution than those under 1 G gravity (100-150 nm).

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