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Thermal Isomerization of Azulene. Single‐Pulse Shock Tube Investigation
Author(s) -
Laskin Alexander,
Lifshitz Assa
Publication year - 1996
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.199600036
Subject(s) - azulene , isomerization , chemistry , photochemistry , arrhenius equation , naphthalene , indene , methylene , medicinal chemistry , activation energy , organic chemistry , catalysis
The thermal isomerization of azulene was studied behind reflected shocks in a pressurized driver single‐pulse shock tube. The temperature range covered was 1050–1400 K at overall densities of ∼2.5 × 10 −5 mol/cm 3 . The main reaction of azulene under these conditions is a unimolecular isomerization to naphthalene, but it also isomerizes, although at a much lower rate, to another isomer. The suggested “tetracyclic triene” intermediate structure for the azulene‐naphthalene isomerization can lead also to transition states that can describe isomerizations to 1‐methylene‐1H‐indene and 1, 2,3‐metheno‐1H‐indene,2,3‐dihydro. Small quantities of C 2 H 2 , C 4 H 2 , C 6 H 6 , and C 6 H 5 ‐C≡CH were also found in the post‐shock samples, particularly at high temperatures. The Arrhenius parameters of the two high pressure limit rate constants for the isomerization processes are: azulene → naphthalene, k 1 = 10 12.93 exp(–62.8 × 10 3 / RT ) s −1 azulene → second isomer, k 2 = 10 12.42 exp(–69.5 × 10 3 / RT ) s −1 A discussion of the mechanism for these isomerization processes is presented.