Mechanism of SNi reactions. The effect of the base strength of the anionic fragments

1978 ◽  
Vol 56 (19) ◽  
pp. 2582-2589 ◽  
Author(s):  
D. J. Verrinder ◽  
M. J. Hourigan ◽  
J. M. Prokipcak
Keyword(s):  
Thermal Decomposition ◽  
Optical Activity ◽  
Ion Pair ◽  
Decomposition Rates ◽  
First Order ◽  
First Order Kinetics ◽  
Cyclic Mechanism ◽  
Base Strength ◽  
Oxygen Bond ◽  
Anionic Fragment

The kinetics and stereochemical aspects of the thermal decomposition of aralkyl carbonates, thiocarbonates, and carbamates were examined. The rates for the decompositions as well as the rates of loss of optical activity followed first-order kinetics. The decompositions appear to involve the heterolysis of the aralkyl–oxygen bond followed by the breakdown of the subsequent ion pair via a cyclic mechanism. However, it was found that this ion pair could return to covalency without completely decomposing to products leading to the racemization of the starting materials. This type of racemization occurred more readily in the case of the carbamates than in the thiocarbonates and carbonates. The dependence of the decomposition rates and the loss of optical activity on the nature of the hetero atom of the anionic fragment of the starting material is discussed.

Mechanisms of SNi Reactions. The Kinetics of the Decomposition of Aralkyl Carbonates

1972 ◽  
Vol 50 (11) ◽  
pp. 1770-1774 ◽  
Author(s):  
J. M. Prokipcak ◽  
T. H. Breckles
Keyword(s):  
Structural Changes ◽  
Elevated Temperatures ◽  
Ion Pair ◽  
Decomposition Rates ◽  
First Order ◽  
First Order Kinetics ◽  
Cyclic Mechanism ◽  
Alkyl Chloroformates ◽  
Kinetics Of ◽  
Oxygen Bond

Anisylic phenyl carbonates decomposed at elevated temperatures to give CO2 and the corresponding anisylic phenyl esters. The decomposition follows first order kinetics very similar to those found for alkyl chloroformates. The decompositions involve the heterolysis of the aralkyl oxygen bond followed by the breakdown of the subsequent ion pair via a cyclic mechanism. The dependence of the decomposition rates on the nature of the solvent and structural changes of the starting carbonates is discussed.

Di-tert-butyl peroxide decomposition behind shock waves

1976 ◽  
Vol 54 (4) ◽  
pp. 581-585 ◽  
Author(s):  
David K. Lewis
Keyword(s):  
Thermal Decomposition ◽  
Gas Phase ◽  
Single Pulse ◽  
First Order ◽  
Tert Butyl ◽  
First Order Kinetics ◽  
Peroxide Decomposition ◽  
Butyl Peroxide ◽  
Temperature Work ◽  
Lower Temperature

The homogeneous, gas phase thermal decomposition of di-tert-butyl peroxide has been studied in a single pulse shock tube. Samples containing 0.05% to 0.5% reactant in argon were heated to 528–677 K at total pressures of about 1 atm. Acetone and ethane were the only significant products. The reaction obeyed first order kinetics. The Arrhenius parameters, log A (s−1) = 15.33 ± 0.50, Eact (kJ/mol) = 152.3 ± 5.8, are in agreement with the bulk of the earlier reported results of lower temperature work, and with a recently reported result obtained via the very low pressure pyrolysis technique. Indications from some of the earlier work that the A factor may decline at high temperatures are not supported by the present study.

Reactions with half-lives of several years

1964 ◽  
Vol 17 (4) ◽  
pp. 406 ◽  
Author(s):  
GA Bottomley ◽  
GL Nyberg
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Gas Phase ◽  
Virial Coefficient ◽  
Energy Equation ◽  
Second Virial Coefficient ◽  
First Order ◽  
First Order Kinetics ◽  
Reciprocal Temperature ◽  
Temperature Activation

The gas-phase thermal decomposition of dimethyldiazirine, (CH3)2CN2, at very slow rates has been investigated using precision gas-volumetric techniques previously applied to second virial coefficient studies. At 50-70� the first-order kinetics correspond to half-lives about 0.3-3.0 years. The present results, together with data obtained by other workers using conventional apparatus at 124-174�, fit a single log rate-reciprocal temperature activation energy equation.

The thermal decomposition of t-alkyl N-arylcarbamates. I. The effect of ring substituents

1967 ◽  
Vol 45 (21) ◽  
pp. 2537-2546 ◽  
Author(s):  
M. P. Thorne
Keyword(s):  
Carbon Dioxide ◽  
Thermal Decomposition ◽  
Phenyl Ring ◽  
Diphenyl Ether ◽  
Decomposition Reaction ◽  
Aromatic Nucleus ◽  
Aryl Group ◽  
First Order ◽  
Cyclic Mechanism ◽  
Decomposition Increase

A series of t-butyl N-arylcarbamates in which the aryl group is a phenyl or a meta- or para-substituted phenyl ring has been prepared. Decomposition of these compounds in diphenyl ether at 177.5 °C has shown that the reaction is essentially first order, yielding carbon dioxide, isobutylene, and the corresponding amine. The rates of decomposition increase with increasing electronegativity of the substituent on the aromatic nucleus, and give a Hammett plot with a slope of 0.54. A cyclic mechanism is proposed for the decomposition reaction.

scholarly journals The dissociation energy of the C-N bond in benzylamine

1949 ◽  
Vol 198 (1053) ◽  
pp. 285-292 ◽  
Keyword(s):  
Activation Energy ◽  
Thermal Decomposition ◽  
Dissociation Energy ◽  
Heat Of Formation ◽  
Molar Ratio ◽  
Kcal Mole ◽  
First Order ◽  
First Order Kinetics ◽  
Permanent Gases ◽  
Kinetics Of

The kinetics of the thermal decomposition of benzylamine were studied by a flow method using toluene as a carrier gas. The decomposition produced NH 3 and dibenzyl in a molar ratio of 1:1, and small quantities of permanent gases consisting mainly of H 2 . Over a temperature range of 150° (650 to 800° C) the process was found to be a homogeneous gas reaction, following first-order kinetics, the rate constant being expressed by k = 6 x 10 12 exp (59,000/ RT ) sec. -1 . It was concluded, therefore, that the mechanism of the decomposition could be represented by the following equations: C 6 H 5 . CH 2 . NH 2 → C 6 H 5 . CH 2 • + NH 2 •, C 6 H 5 . CH 3 + NH 2 •→ C 6 H 5 . CH 2 • + NH 3 , 2C 6 H 5 . CH 2 •→ dibenzyl, and the experimentally determined activation energy of 59 ± 4 kcal./mole is equal to the dissociation energy of the C-N bond in benzylamine. Using the available thermochemical data we calculated on this basis the heat of formation of the NH 2 radical as 35.5 kcal./mole, in a fair agreement with the result obtained by the study of the pyrolysis of hydrazine. A review of the reactions of the NH 2 radicals is given.

Thermal decomposition of citraconic anhydride

1971 ◽  
Vol 24 (4) ◽  
pp. 771 ◽  
Author(s):  
NJ Daly ◽  
F Ziolkowski
Keyword(s):  
Carbon Dioxide ◽  
Thermal Decomposition ◽  
Gas Phase ◽  
Rate Constant ◽  
Arrhenius Equation ◽  
Volume Ratio ◽  
Reaction Vessel ◽  
First Order ◽  
First Order Kinetics ◽  
Citraconic Anhydride

Citraconic anhydride decomposes in the gas phase over the range 440- 490� to give carbon dioxide, carbon monoxide, and propyne which undergoes some polymerization to trimethylbenzenes. The decomposition obeys first-order kinetics, and the Arrhenius equation ������������������� k1 = 1015.64 exp(-64233�500/RT) (s-1) describes the variation of rate constant with temperature. The rate constant is unaffected by the addition of isobutene or by increase in the surface/volume ratio of the reaction vessel. The reaction appears to be unimolecular and if a diradical intermediate is involved it may not be fully formed in the transition state.

The chemistry of N,N′-dimethylformamidine. I. Formation from potassium methylamide and its thermal stability

1978 ◽  
Vol 56 (11) ◽  
pp. 1455-1462 ◽  
Author(s):  
James D. Halliday ◽  
E. Allan Symons ◽  
J. Douglas Bonnett
Keyword(s):  
Thermal Stability ◽  
Thermal Decomposition ◽  
Potassium Salt ◽  
Rate Increase ◽  
Ion Pair ◽  
Concentrated Solutions ◽  
First Order ◽  
Pseudo First Order ◽  
Hydride Elimination ◽  
Rate Limiting

The thermal decomposition of methylamine solutions of potassium methylamide (PMA) to form the potassium salt (PDMFA) of N,N′-dimethylformamidine (DMFA) has been studied as a function of PMA concentration at 60 °C. Although concentrated solutions yield normal pseudo-first-order plots (analysis by ultraviolet–visible spectrophotometry), dilute solutions (< 0.05 mol L−1 PMA) show an increase to a new rate after about 20 h reaction.The mechanism for this novel amidine salt synthesis is discussed in terms of rate-limiting β-hydride elimination from the PMA ion pair. The relatively sharp rate increase with time for the low concentration runs may arise from a slow build up of one or more intermediates. The resulting inverse dependence of kobs on PMA concentration is probably related to ion pair–dimer association phenomena.Pure DMFA has been produced by this reaction, and its thermal stability examined. DMFA decomposes above 100 °C to form bis-N-(N′-methylmethylenimine)methylamine and methylamine; the series of equilibria involved have been shown to be reversible.

The Mechanism for the Thermal Decomposition of E-Aldoxime Carbonates

1975 ◽  
Vol 53 (22) ◽  
pp. 3481-3486 ◽  
Author(s):  
J. M. Prokipcak ◽  
P. A. Forte
Keyword(s):  
Low Temperatures ◽  
Solvent Polarity ◽  
Decomposition Rates ◽  
Cyclic Transition ◽  
First Order ◽  
First Order Kinetics ◽  
Inductive Effects ◽  
Cyclic Transition State ◽  
E And Z Isomers ◽  
Low Entropy

Pyrolysis of aldoxime carbonates at relatively low temperatures (100–120 °C) produced nitriles in excellent yields. These decompositions followed first-order kinetics and the decomposition rates showed little dependence on inductive effects or solvent polarity. Low entropy values along with the fact that the E and Z-isomers behaved quite differently led to the proposal of a cyclic transition state for the decompositions.

Acetolysis of endo-5-Methyltricyclo-[2,2,1,02,6]hept-exo-3-yl and endo-5-Methyltricyclo[2,2,1,02,6]hept-endo-3-yl p-Bromobenzenesulfonates

1979 ◽  
Vol 32 (10) ◽  
pp. 2215 ◽  
Author(s):  
A Dell ◽  
BL Johnson
Keyword(s):  
Reaction Mechanism ◽  
Rate Constants ◽  
Ion Pair ◽  
Comparable Rate ◽  
First Order ◽  
First Order Kinetics

Acetolyses of the title compounds (4b) and (5b) at 25�7� proceed with steady first-order kinetics and with comparable rate constants. Some isomerization of (5b) to (4b) occurred during acetolysis of (5b). The products derived from acetolysis of each p-bromobenzenesulfonate were comparable and included endo-5-methyltricycl0[2,2,1,02,6]hept-exo-3-yl acetate (4c), endo-5-methyltricyclo- [2,2,1,02,6]hept-endo-3-yl acetate (5c), endo-3-methylbicyclo[2,2,1]hept-5-en-exo-2-yl acetate (6) and anti-7-methylbicyclo[2,2,1]hept-5-en-exo-2-yl acetate (7). These results are rationalized in terms of a reaction mechanism involving isomerization of the endo to the exo intimate ion pair, (10) to (ll), as well as a capturable intermediate carbocation which is common to the acetolysis of both p-bromo- benzenesulfonates.

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