Sandmeyer reactions. Part 5. Estimation of the rates of 1,5-aryl/aryl radical translocation and cyclisation during Pschorr fluorenone synthesis with a comparative analysis of reaction energetics
Sa. Chandler et al., Sandmeyer reactions. Part 5. Estimation of the rates of 1,5-aryl/aryl radical translocation and cyclisation during Pschorr fluorenone synthesis with a comparative analysis of reaction energetics, J CHEM S P2, (2), 2001, pp. 214-228
Citations number
56
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
During the Pschorr cyclisation of 2-aroylphenyl radicals, a rearrangement o
ccurs reversibly by 1,5-hydrogen transfer to give 2-benzoylaryl radicals. R
ate constants of (1.2 +/-0.2)x10(6) s(-1) at 293 K are estimated for both t
he forward and back reactions in the equilibrium between 2-(4-methylbenzoyl
)phenyl and 2-benzoyl-5-methylphenyl radicals. Assuming an empirical estima
te of 1.6x10(-2) dm(3) mol(-1) s(-1) for the hypothetical rate of abstracti
on of hydrogen from benzene by phenyl radicals, the radical translocation i
s calculated to occur with a statistically corrected effective molarity of
2.2x10(8) mol dm(-3). By contrast, the competing cyclisation, though occurr
ing at a rate of (8.0 +/-0.9)x10(5) s(-1), exhibits an effective molarity o
f only 5.3 mol dm(-3). The causes of these differences are analysed in term
s of reaction mechanism.