The kinetics of hydrolysis in supercritical water of a series of substituted anisoles to methanol and the corresponding substituted phenol probed the coupling of solvent and substituent effects. For supercritical water concentrations [H20] 5 3 mol/L, the substituent effects exhibited compelling correlation according to the classic Hammett formalism. For [H20] > 5 mol/L, however, the Hammett correlation had an internal minimum at cr = 0, indicative of rate acceleration by both electronwithdrawing and electron-donating substituents. The solvent and substituent effects were thus defined to be "decoupled" for [H20] 5 3 mol/L, where the dielectric constant t I 1.28. The hydrolysisHammett reaction constant increased with decreasing water density. The reaction constant was also of opposite sign to reported values for pyrolysis of substituted benzyl phenyl ethers, suggesting that the practical significance of the present work is the ability to design a substituent-specific solvent effect for selective hydrolysis or pyrolysis.
The Synthesis and the Thermal Decay of 1,2-Diazabenzo(e)semibullvalene and its Relation to the Thermolysis of
BenzobenzvaleneThe [4 + 21-photoadduct of naphthalene and 4-phenyl-4H-l,2,4-triazol-3,5-dione (PTAD) was subjected to a triplet-sensitized di-n-methane rearrangement. Hydrolysis of the resulting urazol15 gave a stable semicarbazide 16 which by nickel-peroxide oxidation gave 1,2-diazabenzo[e]semibullvalene (10). At 40"C, the latter decays in CHCI, solution to produce benzofulvene (2) as the principal product, accompanied by benzobenzvalene (1) and small amounts of naphthalene. This decay reaction is rationalized in terms of a 1,3-dipolar cycloreversion which is followed by denitrogenation to give indenyl carbene (19). The thermolysis of 1 in solution is believed to proceed via the same carbene. At present, these findings provide only a partial answer to the benzobenzvalene enigma (i.e., in solution at 150", 1 gives 2, but in the gas-phase at 300", 1 yields naphthalene). MeOH is shown to add readily to 10 in a homologous Michael addition.
1 3.1X. 89) ~~ ~ ~~ ~Starting from dibenzo [u,c]cyclooctene (4) and 4-methyl-3H-1,2,4-triazol-3,5(4H)-dione (MTAD), the strained skeleton of the title azo compound 1 is assembled in a tandem photo-Diels-Alder addition/di-n-methane rearrangement sequence. The synthesis is completed by a stepwise hydrolytic oxidation of the ensuing triazolidinedione 2 with nickel peroxide. Thermolysis of 1 in benzene solution is shown to be governed by an initial 1,3-dipolar cycloreversion which leads, via an intermediate diazo compound 11, to cyclobuta[l]phenanthrene 8 and two further carbene-derived C,,H,, products. Photolysis of 1 at 350 nrn leads in modest yield (12%). viu a diazenyl diradical, to an unstable bridged bicyclobutane 10 (dibenzooctavalcne). MNDO calculations suggest the latter to have a rapidly inverting, twisted structure of Cz symmetry.
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