Novel Catalysis of Hydroquinone Autoxidation with Nitrogen Oxides
作者:E. Bosch、R. Rathore、J. K. Kochi
DOI:10.1021/jo00088a039
日期:1994.5
An efficient catalytic method is described for the preparative conversion of hydroquinones to quinones with dioxygen under mild conditions. The use of the gaseous nitrogen oxide (NOx) catalyst allows a simple workup procedure for the isolation of quinones in essentially quantitative yields by merely removing the low-boiling solvent dichloromethane in vacuo. The mechanism of the catalytic autoxidation of hydroquinones is ascribed to the critical role of nitrosonium (NO+) in the one-electron oxidation of hydroquinone, followed by the reoxidation of the reduced nitric oxide (NO) with dioxygen. An extensive series of complex interchanges among various NOx species in nitrogen-(V), -(IV), -(III), and -(II) oxidation states, coupled with stepwise oxidation of hydroquinone via a successive series of one-electron/proton transfers, form the critical components of the catalytic cycle.
US4146559A
申请人:——
公开号:US4146559A
公开(公告)日:1979-03-27
Isolation of Novel Radical Cations from Hydroquinone Ethers. Conformational Transition of the Methoxy Group upon Electron Transfer
作者:Rajendra Rathore、Jay K. Kochi
DOI:10.1021/jo00119a017
日期:1995.7
Hydroquinone ethers as the bis-annulated derivatives R1-R3 are excellent electron donors by virtue of the facile oxidation to their radical cations R1(.+), R2(.-), and R3(.-) that are readily isolable as unusually robust SbCl6- and BF4- salts persistent in air for prolonged periods. Although the gas-phase vertical ionization potentials of the methyl ethers R1a and R2a are the same (IP = 7.83 +/- 0.01 eV), the oxidation potential of R1a in dichloromethane solution is less positive than that of R2a (E(1/2) = 1.11 and 1.30 V, respectively). The significantly lower value of E(1/2) for R1a relative to R2a, despite minimal changes in structure, is attributed to the conformational change that can occur in the radical cation. Indeed, X-ray crystallographic analysis of R1a, R2a, and R1a(.-) shows that the increased donor strength of R1a is derived from the enhanced (resonance) stabilization of R1a(.-), in which the methoxy group undergoes a 90 degrees rotation to the favorable coplanar conformation with respect to the aromatic ring. The subtle variation in the molecular structures of R1 and R2 accounts for the difference in nonbonded steric effects arising from the bridgehead alpha-hydrogens toward the methoxy groups.