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Author Kresge, A. J. ♦ Chiang, Y.
Sponsorship USDOE
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Publisher American Chemical Society (ACS)
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY ♦ ACIDS ♦ AROMATIC HYDROCARBONS ♦ AROMATICS ♦ BENZENE ♦ BROENSTED THEORY ♦ CATALYSIS ♦ HYDROGEN ♦ ISOTOPIC EXCHANGE ♦ METHOXY RADICALS ♦ PROTONS ♦ REACTION KINETICS ♦ TRANSFER FUNCTIONS ♦ TRITIUM ♦ WATER
Abstract General acid catalysis was detected in the exchange of aromatic hydrogen of trimethoxybenzene: rates of loss of tritium from 1,3,5-trimethoxybenzene-2-t to seven acids ranging in strength from H<sub>3</sub>O<sup>+</sup> to H<sub>2</sub>O conform to the Bronsted relation k<sub>A</sub> = 4.72 x 10<sup>-2</sup> (K<sub>A</sub>)<sub>0.5</sub><sub>18</sub> . This fact is inconsistent with a previously assigned mechanism for aromatic The si le formation of a loose complex between proton and aromatic substrate followed by slow intramolecular isomerization of this complex. Instead, general acid catalysis indicates a simple slow proton transfer mechanism for exchange. The loss of tritium from 1,3,5-trimethoxybenzene2-t is not catalyzed by bases. This shows that the proton transfer is not a concerted process, but that reaction takes place in two discrete steps: proton addition to give a phenonium ion followed by proton abstraction to give exchanged trimethoxybenzene. This mechanism, unlike the one first proposed for aromatic hydrogen exchange, is wholly consistent with generally accepted mechanistic schemes for other electrophilic aromatic substitutions.
ISSN 00027863
Educational Use Research
Learning Resource Type Article
Publisher Date 1961-07-01
Publisher Department Brookhaven National Lab., Upton, N.Y.
Journal Journal of the American Chemical Society
Volume Number 83
Issue Number 13
Organization Brookhaven National Lab., Upton, N.Y.


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