The mechanism of the pyrolysis of 2, 2, 3, 3-tetramethylbutane

The pyrolysis of 2, 2, 3, 3-tetramethylbutane (TMB) was investigated in the ranges 699-735 K and 3-19 Torr (0.4-2.5 kPa) at up to 4% decomposition. The reaction is strongly self-inhibited and sensitive to the surface/volume ratio of the reaction vessel. A simple Rice-Herzfeld chain terminated by the heterogeneous removal of hydrogen atoms is proposed for the initial, uninhibited reaction generating isobutene and hydrogen in a 2:1 ratio. Self-inhibition is due to abstraction by hydrogen atoms of hydrogen atoms from product isobutene giving resonance-stabilized 2-methylallyl radicals which participate in homogeneous termination reactions. The kinetic characteristics of the major primary products (> 95% on a mole basis), isobutene and hydrogen, are accounted for when reasonable values are assumed for the rate constants for hydrogen atom abstraction by hydrogen atoms from TMB and from isobutene and for initiation and heterogeneous termination of the chain reaction. The kinetic characteristics of the formation of methane and propene (2-4% of total product) are accounted for by the secondary reaction scheme H + i-C 4 H 8 → i-C 4 H 9 , i-C 4 H 9 → CH 3 + C 3 H 6 , CH 3 + TMB → CH 4 + C 8 H 17 , when a reasonable value for the rate constant for the hydrogen atom addition to isobutene is assumed. The kinetic characteristics of the formation of ethene ( ca . 0.1% of total product) are accounted for by the tertiary reaction scheme H + C 3 H 6 → n -C 3 H 7 n -C 3 H 7 → CH 3 + C 2 H 4 , when a reasonable value for the rate constant for the hydrogen atom addition to propene is assumed. The kinetic characteristics of the formation of isobutane ( ca . 1% of total product) are much less affected by an increase in surface/volume ratio of the reactor than are those of the other products. A heterogeneous, secondary source is suggested, viz. 1/2H 2 ( g ) ⇌ H (wall), H (wall) + t-C 4 H 9 ( g ) ⇌ i-C 4 H 10 ( g ), which can generate the observed dependence of the isobutane yield on the reaction conditions but the reasonableness or otherwise of the values of the equilibrium and rate constants it is necessary to postulate is impossible to assess without further work designed specifically to investigate this problem.

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BrHgO• + C2H4 and BrHgO• + HCHO in Atmospheric Oxidation of Mercury: Determining Rate Constants of Reactions with Pre-Reactive Complexes and a Bifurcation

10.26434/chemrxiv.8266733.v1 ◽

2019 ◽

Author(s):

Khoa T. Lam ◽

Curtis J. Wilhelmsen ◽

Theodore Dibble

Keyword(s):

Hydrogen Atom ◽

Quantum Chemistry ◽

Transition State ◽

Rate Constant ◽

Rate Constants ◽

Minimum Energy ◽

Atmospheric Oxidation ◽

Minimum Energy Path ◽

Oh Radical ◽

Hydrogen Atoms

Models suggest BrHgONO to be the major Hg(II) species formed in the global oxidation of Hg(0), and BrHgONO undergoes rapid photolysis to produce the thermally stable radical BrHgO•. We previously used quantum chemistry to demonstrate that BrHgO• can, like OH radical, readily can abstract hydrogen atoms from sp3-hybridized carbon atoms as well as add to NO and NO2. In the present work, we reveal that BrHgO• can also add to C2H4 to form BrHgOCH2CH2•, although this addition appears to proceed with a lower rate constant than the analogous addition of •OH to C2H4. Additionally, BrHgO• can readily react with HCHO in two different ways: either by addition to the carbon or by abstraction of a hydrogen atom. The minimum energy path for the BrHgO• + HCHO reaction bifurcates, forming two pre-reactive complexes, each of which passes over a separate transition state to form a different product.

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BrHgO• + C2H4 and BrHgO• + HCHO in Atmospheric Oxidation of Mercury: Determining Rate Constants of Reactions with Pre-Reactive Complexes and a Bifurcation

10.26434/chemrxiv.8266733 ◽

2019 ◽

Author(s):

Khoa T. Lam ◽

Curtis J. Wilhelmsen ◽

Theodore Dibble

Keyword(s):

Hydrogen Atom ◽

Quantum Chemistry ◽

Transition State ◽

Rate Constant ◽

Rate Constants ◽

Minimum Energy ◽

Atmospheric Oxidation ◽

Minimum Energy Path ◽

Oh Radical ◽

Hydrogen Atoms

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Radiolysis studies on the corrosion inhibitors 1 -hexyn-3-ol, cinnamonitrile, and 1,3-diethyl-2-thiourea

Canadian Journal of Chemistry ◽

10.1139/v95-264 ◽

1995 ◽

Vol 73 (12) ◽

pp. 2137-2142 ◽

Cited By ~ 1

Author(s):

A.J. Elliot ◽

M.P. Chenier ◽

D.C. Ouellette

Keyword(s):

Hydrogen Atom ◽

Hydroxyl Radical ◽

Temperature Dependence ◽

Rate Constant ◽

Rate Constants ◽

Corrosion Inhibitors ◽

Hydrated Electron

In this publication we report: (i) the rate constants for reaction of the hydrated electron with 1-hexyn-3-ol ((8.6 ± 0.3) × 108 dm3 mol−1 s−1 at 18 °C), cinnamonitrile ((2.3 ± 0.2) × 1010 dm3 mol−1 s−1 at 20 °C), and 1,3-diethyl-2-thiourea ((3.5 ± 0.3) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile and diethylthiourea, the temperature dependence up to 200 °C and 150 °C, respectively, is also reported; (ii) the rate constants for the reaction of the hydroxyl radical with 1-hexyn-3-ol ((5.5 ± 0.5) × 109 dm3 mol−1 s−1 at 20 °C), cinnamonitrile ((9.2 ± 0.3) × 109 dm3 mol−1 s−1 at 21 °C), and diethylthiourea ((8.0 ± 0.8) × 108 dm3 mol−1 s−1 at 22 °C). For cinnamonitrile, the temperature dependence up to 200 °C is also reported; (iii) the rate constant for the hydrogen atom reacting with 1-hexyn-3-ol ((4.3 ± 0.4) × 109 dm3 mol−1 s−1 at 20 °C). Keywords: radiolysis, corrosion inhibitors, rate constants.

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The reaction of hydrogen atoms with ethylene

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1970.0097 ◽

1970 ◽

Vol 316 (1527) ◽

pp. 575-591 ◽

Cited By ~ 35

Keyword(s):

Hydrogen Atom ◽

Rate Constant ◽

Recombination Reaction ◽

Methyl Radicals ◽

Methyl Radical ◽

Hydrogen Atoms ◽

Ethyl Radical ◽

Cracking Reaction ◽

Computer Calculations ◽

First Time

A detailed study has been made of the products from the reaction between hydrogen atoms and ethylene in a discharge-flow system at 290 ± 3 K. Total pressures in the range 8 to 16 Torr (1100 to 2200 Nm -2 ) of argon were used and the hydrogen atom and ethylene flow rates were in the ranges 5 to 10 and 0 to 20 μ mol s -1 , respectively. In agreement with previous work, the main products are methane and ethane ( ~ 95%) together with small amounts of propane and n -butane, measurements of which are reported for the first time. A detailed mechanism leading to formation of all the products is proposed. It is shown that the predominant source of ethane is the recombination of two methyl radicals, the rate of recombination of a hydrogen atom with an ethyl radical being negligible in comparison with the alternative, cracking reaction which produces two methyl radicals. A set of rate constants for the elementary steps in this mechanism has been derived with the aid of computer calculations, which gives an excellent fit with the experimental results. In this set, the values of the rate constant for the addition of a hydrogen atom to ethylene are at the low end of the range of previously measured values but are shown to lead to a more reasonable value for the rate constant of the cracking reaction of a hydrogen atom with an ethyl radical. It is shown that the recombination reaction of a hydrogen atom with a methyl radical, the source of methane, is close to its third-order region.

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An anomalous effect of methyl group on acidity of acylthioureas

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19871992 ◽

1987 ◽

Vol 52 (8) ◽

pp. 1992-1998 ◽

Cited By ~ 6

Author(s):

Jaromír Kaválek ◽

Josef Jirman ◽

Vladimír Macháček ◽

Vojeslav Štěrba

Keyword(s):

Hydrogen Atom ◽

Rate Constant ◽

Rate Constants ◽

Dissociation Constants ◽

Acetyl Derivative ◽

Methyl Groups ◽

Anomalous Effect ◽

Methyl Group ◽

Methyl Derivatives

Dissociation constants and methanolysis rate constants have been measured of 1-acetyl- and 1-benzoylthioureas and their N-methyl derivatives. Replacement of hydrogen atom at N(1) (next to the acyl group) by methyl group increases the acidity of the benzoyl derivative by one order, that of the acetyl derivative by as much as two orders of magnitude. Replacement of both hydrogens at N(3) by methyl groups lowers the methanolysis rate constant by more than two orders, whereas the replacement of hydrogen atom at N(1) by methyl group increases the methanolysis rate by the factor of 30.

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Shock-wave observations of rate constants for atomic hydrogen recombination from 2500 to 7000 °K: collisional stabilization by exchange of hydrogen atoms

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1969.0074 ◽

1969 ◽

Vol 310 (1501) ◽

pp. 253-276 ◽

Cited By ~ 34

Keyword(s):

Shock Waves ◽

Rate Constant ◽

Rate Constants ◽

Atomic Hydrogen ◽

Functional Form ◽

Kcal Mole ◽

Hydrogen Atoms ◽

Hydrogen Molecules ◽

Hydrogen Recombination ◽

Equilibrium Dissociation

Rate constants for the recombination of atomic hydrogen with hydrogen molecules, hydrogen atoms, and argon atoms as the third bodies are presented in functional form for the range of temperatures from about 2500 to 7000 °K and are critically compared with the results of other workers. The rate constants are evaluated from detailed analyses of spectrum-line reversal measurements of the fall in temperature accompanying dissociation behind shock waves in gas mixtures containing 20, 40, 50 and 60% of hydrogen in argon. The rate constants for recombination with hydrogen molecules ( k -1 ) and argon atoms ( k -3 ) fit the equations log 10 k -1 = 15.243 - 1.95 x 10 -4 T cm 6 mole -2 s -1 , log 10 k -3 = 15.787 - 2.75 x 10 -4 T cm 6 mole -2 s -1 , with a standard deviation of 0.193 in log 10 k -1 . The rate constant for recombination with hydrogen atoms is about ten times larger than these at 3000 °K and shows a steep inverse dependence on temperature ( ~ T -6 ) above 4000 °K. Below this temperature the power of this dependence decreases rapidly and there is strong evidence that the value of this rate constant has a maximum around 3000 °K. This behaviour is interpreted on the basis of a process of collisional stabilization by atom exchange, requiring an activation energy around 8 kcal mole -1 and taking place under conditions of vibrational adiabaticity. The over-all results indicate that the assumption of equality between the equilibrium constant and the ratio of the rate constants for dissociation and recombination is valid throughout the region of non-equilibrium dissociation and at all temperatures in the shock waves examined.

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Determination of the Rates of Hydrogen Atom Reaction with NO by a Modulation Technique

Canadian Journal of Chemistry ◽

10.1139/v73-054 ◽

1973 ◽

Vol 51 (3) ◽

pp. 370-372 ◽

Cited By ~ 14

Author(s):

R. Atkinson ◽

R. J. Cvetanović

Keyword(s):

Nitric Oxide ◽

Hydrogen Atom ◽

Phase Shift ◽

Rate Constants ◽

Hydrogen Atoms ◽

Arrhenius Parameters ◽

Modulation Technique ◽

The Absolute

A modulation technique has been used to determine from phase shift measurements the absolute values of the rate constants and the Arrhenius parameters of the reaction of hydrogen atoms with nitric oxide.

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Cooperative Hydrogen Atom Transfer: From Theory to Applications

Synlett ◽

10.1055/a-1463-9527 ◽

2021 ◽

Author(s):

Padmanabha Venkatesh ◽

Julian G West

Keyword(s):

Organic Chemistry ◽

Hydrogen Atom ◽

Closed Shell ◽

Reaction Scheme ◽

Hydrogen Atom Transfer ◽

Radical Center ◽

Atom Transfer ◽

Hydrogen Atoms ◽

Strength Differential ◽

Radical Reduction

Hydrogen atom transfer (HAT) is one of the fundamental transformations of organic chemistry, allowing for the interconversion of open and closed shell species through the concerted movement of a proton an electron. While the value of this transformation is well-appreciated in isolation, allowing for homolytic C–H activation via abstractive HAT and radical reduction via donative HAT, cooperative HAT (cHAT) reactions, where two hydrogen atoms are removed or donated to vicinal reaction centers in succession proceeding through radical intermediates, are comparatively unknown outside of the mechanism of desaturase enzymes. This tandem reaction scheme has important ramifications in the thermochemistry of each HAT, with the bond dissociation energy of the C–H bond adjacent to the radical center being significantly lowered compared to that of the parent alkane, allowing for each HAT to be performed by different species. Here we discuss the thermodynamic basis of this bond strength differential in cHAT and demonstrate its use as a design principle in organic chemistry for both dehydrogenative (application 1) and hydrogenative (application 2) reactions. Together, we hope that this overview will highlight the exciting reactivity possible with cHAT and inspire further development using this mechanistic approach.

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Monte-Carlo simulation of hydrogen-atom recombination

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1973.0071 ◽

1973 ◽

Vol 333 (1595) ◽

pp. 419-434 ◽

Cited By ~ 10

Keyword(s):

Hydrogen Atom ◽

Cross Section ◽

Rate Constant ◽

Relative Velocity ◽

Classical Trajectory ◽

Hydrogen Atoms ◽

Order Of Magnitude ◽

The Cross ◽

The Right ◽

Right Order

Classical trajectory calculations have been used to calculate the cross-section (and hence the rate constant) for the recombination of hydrogen atoms on a third hydrogen atom, in the temperature range 500–6000 K. The model involves the stabilization of a quasi-bound molecule in an encounter with the third atom. The results indicate that the cross-section for direct stabilization is small and insensitive to the relative velocity, whereas the cross-section for exchange stabilization is large at low velocities and decreases rapidly as the relative velocity is increased. The calculated rate constant, although of the right order of magnitude at 500 K, does not exhibit the anomalous features previously observed experimentally at higher temperatures.

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Rate constants for the reaction of the hydrogen atom with aliphatic ketones in water

Canadian Journal of Chemistry ◽

10.1139/v97-133 ◽

1997 ◽

Vol 75 (8) ◽

pp. 1114-1119 ◽

Cited By ~ 1

Author(s):

Stephen P. Mezyk ◽

Annett Lossack ◽

David M. Bartels

Keyword(s):

Hydrogen Atom ◽

Rate Constants ◽

Radical Scavenger ◽

Hydrogen Atoms ◽

Paramagnetic Resonance ◽

Kinetic Measurements ◽

Aliphatic Ketones ◽

Hydroxyl Radical Scavenger ◽

Free Induction ◽

Electron Paramagnetic

Arrhenius parameters for the reaction of hydrogen atoms with 3-methyl-2-butanone, 3-pentanone, cyclopentanone, 4-methyl-2-pentanone, and 2-butanone in aqueous solution have been directly calculated from electron paramagnetic resonance free induction decay (FID) attenuation measurements. For these compounds, absolute scavenging rate constants at 25.0 °C of (8.84 ± 0.26) × 107, (4.20 ± 0.15) × 107, (4.91 ± 0.28) × 107, (3.25 ± 0.27) × 107, and (2.20 ± 0.32) × 107 dm3 mol−1 s−1, with corresponding activation energies of 17.43 ± 0.29, 20.69 ± 0.31, 18.73 ± 0.36, 22.24 ± 0.80, and 22.30 ± 1.04 kJ mol−1 were determined, respectively. Competition kinetic measurements based on total H2 yields have established that for all of these ketones the dominant hydrogen atom reaction path is by •H atom abstraction. The new activation energy for 2-butanone is much lower than the previously reported value of 40.1 ± 0.7 kJ mol−1 with this difference attributed to interfering reactions from the added bromide previously used as a hydroxyl radical scavenger. Keywords: Arrhenius, kinetics, hydrogen atom, aqueous, ketones.

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