Wasserstoffübertragungen, Teil 2. Radikalmechanismus der thermischen Disproportionierung des 1,2‐Dihydronaphthalins

Abstract

Bei der thermischen Disproportionierung von 1,2-Dihydronaphthalin (1) verlaufen Wasserstoffabspaltung und -addition als sterisch unspezifische Radikalreaktionen. Ein Synchronmechanismus2) wurde ausgeschlossen. Hydrogen Transfer Reactions, Part 2*) Radical Mechanism of Thermal Disproportionation of 1,2-DihydronaphthaleneIn the thermal disproportionation of 1,2-dihydronaphthalene (1) both hydrogen abstraction and addition are stereo-unspecific radical reactions. An electrocyclic mechanism2) was excluded.Thermische Disproportionierungen werden bei Dihydroaromaten oft gefunden, da hier das als Wasserstoffdonator wirkende Molekul unter Gewinn an Mesomerieenergie in den aromatischen Zustand iibergeht . Verschiedene Mechanismen werden diskutiert .So fand man bei der Gasphasen-Disproportionierung von 1,3-Cyclohexadien (bei ca. 300°C) einen Radikalmechani~mus~). Dagegen postulierten Gill und Hawkins') fur die thermische Disproportionierung von 1 ,2-Dihydronaphthalin (1) in Naphthalin (2) und Tetralin (3), die sie in LLisung bei ca. 300°C kinetisch verfolgten, einen konzertierten Ablauf. Eine Gruppenubertragung dieser Stereochemie ist im Grundzustand symmetrieerlaubt 'I. Wir haben dideuterierte 1,2-Dihydronaphthaline in hoher Isotopenreinheit hergestellt und mit ihrer Hilfe den Ablauf der thermischen Disproportionierung von 1 untersucht . Deuterierte AusgangsverbindungenEs wurden folgende Isotopomeres) synthetisiert:

Asphaltene reaction pathways. 4. Pyrolysis of tridecylcyclohexane and 2-ethyltetralin

“…A set of representative free-radical reaction steps accounting for the formation of both the primary and secondary products of 2ET pyrolysis is given in parts a and b of Figure 8, respectively. These were selected based on elementary reactions previously proposed (Allen and Gavalas, 1983; Heesing and Mullers, 1980;King and Stock, 1981;Franz et al, 1984; Bredael and Vinh, 1979) for the thermal reactions of tetralin and related compounds.…”

“…By analogy, the 2-ethyldialins can be expected to pyrolyze to 2-ethylnaphthalene and 2-ethyltetralin. Figure 8b summarizes the elementary reaction steps (Allen and Gavalas, 1983; Franz et al, 1984;Gill et al, 1974;Heesing and Mullers, 1980) likely responsible for the formation of the secondary products. The reaction mechanism includes chain propagation by the addition of hydrogen, hydrogen abstraction, and ß scission, with hydrogen atom serving as the principal chain carrier.…”

Thermal Cleavage of the One-Atom Aryl−Hydroaryl Bridge in 2-(1-Naphthylmethyl)-3,4-dihydronaphthalene

“…The results discussed above show that the reaction network for NMDN neat pyrolysis must include primary pathways from NMDN to dinaphthylmethane, 1-methylnaphthalene, dialin, naphthyltetralylmethane, and naphthalene. Tetralin is formed in secondary pathways, possibly from the thermal reactions of dialin − or decomposition of naphthyltetralylmethane.…”

Thermolysis of phenyl-substituted 1,2-dihydronaphthalenes. Evidence for diphenylbutadienes as intermediates

“…spectra were recorded on a Bruker WH-90 or WH-500 spectrometer in CDCl,. 6 Values are reported relative to SiMe, as internal standard. Mass spectra were recorded on a Varian MAT SM-2B or a Finnigan 2000 quadruple mass spectrometer, and U.V.…”

“…Crystallization from methanol afforded a pure compound of (20) (5.7 g, 15%) as a white powder, m.p. 6 4-(p-Tolyl)-1,2-dihydronaphthulene (34).-This was synthesized from p-methylbenzylmagnesium bromide and 1 -0xotetrahydronaphthalene followed by dehydration, according to the method of von Braun.22…”