1,2-dihydronaphthalene disproportionation

Virk and co-workers (24b,c) and King and Stock (35b) have reported rates for H2-transfer to anthracene and phenanthrene in solution containing 1,2- and 1,4-dihydronaphthalene and tetralin. Comparisons between reported rate constants and estimated rate constants for bimolecular disproportionation are given in Table VI. In agreement with Stock, this data does not provide evidence for a concerted H2-transfer mechanism. Our calculations indicate that molecular disproportionation may be a major hydrogenation mechanism in these reaction systems. 

Formation of Free Radicals by Molecular Disproportionation. A significant conclusion that may be drawn from considerations of rate and equilibrium constants for molecular disproportionation is that this path can provide appreciable concentrations of free radicals in many systems long after most weak chemical bonds have ruptured and bond homolysis has ceased to be a major source of free radicals. In "pure tetralin, for instance, trace concentrations of 1,2-dihydronaphthalene are expected to equilibrate with tetralin and tetralyl radicals,... 

It is interesting to note that catalytic reactions tending to equilibrate tetralin, 1,2-dihydronaphthalene and naphthalene (19,39) will serve to generate free radicals since 1,2-dihydronaphthalene rapidly undergoes molecular disproportionation with tetralin. For instance, at equilibrium a 0.5% solution of naphthalene in tetralin (typical of distilled tetralin) will generate ca. 10 2 mol percent 1,2-dihydronaphthalene at 400°C, which will, in turn, form ca. 10 7 M tetralyl radicals (see above). 

Isomerization and disproportionation of the monomer are also often observed with other systems. 1,4-Dihydro naphthalene is first isomerized to 1,2-dihydronaphthalene under the influence of sodium naphthalene and then anionically polymerized. The presence of M0O3 on carriers causes propylene to disproportionate to ethylene and butene-2 and then the ethylene polymerizes. 

Figure 31.5 Porosity effects The kinetics of the SG-1-catalyzed disproportionation reactions (see Figure 31.4) of substrates of different sizes. From left to right 1,3-cyclohexa-diene (g), 1,2-dihydronaphthalene (Al. 1,2-...

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