Gas-phase pyrolysis of isotopically stereochemically labeled .alpha.-pinene.  Evidence for a non-randomized intermediate

Gajewski, Joseph J.; Hawkins, Christopher M.

doi:10.1021/ja00264a047

Cited by 19 publications

(23 citation statements)

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“…Moreover, the hydroxyl group present in 2-pinanol is not directly involved in the transition states of initial fragmentations and biradical rearrangements. Furthermore, other studies of the analogous ␣-pinene have resulted in very similar pre-exponential factors for the corresponding reactions [44,59], even more corroborating the mechanistic and kinetic similarities of bicyclic monoterpenes. Therefore, the values used for the pre-exponential factors are 1.0 × 10 14 s −1 for the cyclobutane fragmentations (A,B) and 0.6 × 10 14 s −1 for the subsequent rearrangement of the biradicals (C,E).…”

Section: Pre-exponential Factorssupporting

confidence: 62%

“…Trans-β-terpineol Dervan et al [42,43] examined the kinetics of butadiyl biradical rearrangements and concluded that their further cleavage to ethylene occurs faster than their recombination to cyclic structures. Gajewski and Hawkins [44] investigated the pyrolysis of deuterium labeled ␣-pinene and concluded that the monocyclic racemic limonenes were formed through a [1,5]-H-shift of the biradical intermediate. Semikolenov et al [10,25,45] studied the isomerization kinetics of mixtures of cis-and trans-2-pinanol in a fixed-bed reactor type with a heat conducting carbon monolith catalyst and reported a higher reactivity for the cis-isomer relative to the trans-isomer.…”

Section: Introductionmentioning

confidence: 99%

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Kinetic study of the thermal rearrangement of cis- and trans-2-pinanol

Vandewiele

Reyniers

Marin

2011

Journal of Analytical and Applied Pyrolysis

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Section: Pre-exponential Factorssupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Kinetic study of the thermal rearrangement of cis- and trans-2-pinanol

Vandewiele

Reyniers

Marin

2011

Journal of Analytical and Applied Pyrolysis

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“…"-', The products vary with the catalyst: PhCH,NEt,+ C1-gives the diaddition products (l40), as does Me,,NC,,H,,+ Br-,"l" the more hydrophilic Me," CI-yielding specifically monoaddition products, Oxidation of limonene by manganese(ri1) acetate in acetic acid results in radical addition, giving the acid (149), in 38% yield,""' and the lactone ( I 50). 352 Despite this relatively good yield, the reported overall yield of the alcohol (145) was only 8 Gardrat converted (149) into (150) directly by the action of formic acid, in 43% isolated yield from limonene. """…”

Section: Addition Of a C Unit To Limonenementioning

confidence: 99%

Limonene

Thomas¹,

Bessière²

1989

Nat. Prod. Rep.

111

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“…15 When the temperature in creases to 430 °C, the conversion increases insignifi cantly (~8%) and α and β pyronenes appear along with α pinene; however, alloocimenes are entirely absent in the reaction mixture. According to the proposed mechanism (see Scheme 1), pyronenes are formed from alloocimenes due to intramolecular cyclization.…”

Section: Resultsmentioning

confidence: 99%

Thermolysis of α-pinene in supercritical lower alcohols

et al. 2006

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Thermal isomerization of α pinene in supercritical solvents, viz., ethanol, methanol, and propan 1 ol, was carried out, and differences in the rate and selectivity of the process were revealed. In supercritical ethanol the reaction rate increases sharply and the selectivity remains unchanged with an increase in the temperature (from 290 to 390 °C) or pressure (from 90 to 270 atm). The main reaction products are limonene, isomeric alloocimenes, and pyronenes. The selectivity for limonene in propan 1 ol is higher than in other alcohols when the conver sion of α pinene not higher than 50%. In supercritical ethanol (430 °C, 120 atm, 140 s) limonene is more stable than α pinene (conversion 8%).Organic synthesis in supercritical media is a modern, dynamically developing branch of organic chemistry. 1-4 However, transformations of terpenoid hydrocarbons and their functional derivatives in supercritical media remain virtually unstudied. Only single examples for the catalytic hydrogenation of terpenoids in supercritical CO 2 5 and subcritical water 6 are known, as well as the esterification of some terpenoid alcohols. 7The purpose of the present work is to study transfor mations of α pinene in supercritical alcohols (methanol, ethanol, and propan 1 ol) and reveal a relationship of the temperature and pressure to the reaction rate and the influence of the residence time on the conversion. Experimental(+) α Pinene (>98%) and (+) limonene (>97%) were pur chased from Aldrich.Thermal isomerization under supercritical conditions was carried out in a laboratory setup using a tubular flow type reac tor 6 m long and 1.75 mm in diameter (the reactor volume was about 14 cm 3 ). A solution of the starting substance was supplied by a piston pump to the reactor from which the reaction mixture was transferred to a heat exchanger for subsequent cooling and further to a separator where samples for analysis were taken.The composition of the reaction products was analyzed by the GC MS method on a Hewlett Packard 5890/II gas chro matograph with an HP MSD 5971 quadrupole mass spectrom eter as a detector. An НР 5 quartz column (30 m × 0.25 mm) was used (copolymer of 5% diphenyl and 95% dimethylsiloxane as the stationary phase, the film thickness 0.25 µm); the carrier gas was helium with a constant flow rate of 1 mL min -1 ; the injector temperature was 280 °C; temperature program ming: 50 °C (2 min), 50-200 °C (4 °C min -1 ), 200-300 °C (20 °C min -1 ), 300 °C (20 min); the energy of ionizing electrons was 70 eV. Qualitative analysis was performed comparing reten tion indices of components and their complete mass spectra with the corresponding data for pure compounds if any and with the data of the Wiley7 library of mass spectrometric data (375000 mass spectra) and catalogue. 8 The percentage composi tion of mixtures was calculated from the surface areas of chro matographic peaks using no correction coefficients. Results and DiscussionThe behavior of α pinene in supercritical 96% ethanol was studied at T = 290-390 °C and P = 90-270 atm, which ...

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Gas-phase pyrolysis of isotopically stereochemically labeled .alpha.-pinene. Evidence for a non-randomized intermediate

Cited by 19 publications

References 0 publications

Kinetic study of the thermal rearrangement of cis- and trans-2-pinanol

Kinetic study of the thermal rearrangement of cis- and trans-2-pinanol

Limonene

Thermolysis of α-pinene in supercritical lower alcohols

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