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Title: Slow Proton Transfer Reactions. III. The Mechanism of Acid-catalyzed Aromatic Hydrogen Exchange in 1,3,5-Trimethoxybenzene 1,2

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 3O + to H 2O conform to the Bronsted relation k A = 4.72 x 10 -2 (K A) 0.5 18 . 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.

Authors:
;
Publication Date:
Research Org.:
Brookhaven National Lab., Upton, N.Y.
Sponsoring Org.:
USDOE
OSTI Identifier:
4009718
NSA Number:
NSA-15-025948
Resource Type:
Journal Article
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 83; Journal Issue: 13; Other Information: Orig. Receipt Date: 31-DEC-61; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
Country unknown/Code not available
Language:
English
Subject:
37 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

Citation Formats

Kresge, A. J., and Chiang, Y. Slow Proton Transfer Reactions. III. The Mechanism of Acid-catalyzed Aromatic Hydrogen Exchange in 1,3,5-Trimethoxybenzene 1,2. Country unknown/Code not available: N. p., 1961. Web. doi:10.1021/ja01474a022.
Kresge, A. J., & Chiang, Y. Slow Proton Transfer Reactions. III. The Mechanism of Acid-catalyzed Aromatic Hydrogen Exchange in 1,3,5-Trimethoxybenzene 1,2. Country unknown/Code not available. doi:10.1021/ja01474a022.
Kresge, A. J., and Chiang, Y. Sat . "Slow Proton Transfer Reactions. III. The Mechanism of Acid-catalyzed Aromatic Hydrogen Exchange in 1,3,5-Trimethoxybenzene 1,2". Country unknown/Code not available. doi:10.1021/ja01474a022.
@article{osti_4009718,
title = {Slow Proton Transfer Reactions. III. The Mechanism of Acid-catalyzed Aromatic Hydrogen Exchange in 1,3,5-Trimethoxybenzene 1,2},
author = {Kresge, A. J. and Chiang, Y.},
abstractNote = {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 H3O+ to H2O conform to the Bronsted relation kA = 4.72 x 10-2 (KA)0.518 . 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.},
doi = {10.1021/ja01474a022},
journal = {Journal of the American Chemical Society},
issn = {0002-7863},
number = 13,
volume = 83,
place = {Country unknown/Code not available},
year = {1961},
month = {7}
}