Slow Proton Transfer Reactions. III. The Mechanism of Acid-catalyzed Aromatic Hydrogen Exchange in 1,3,5-Trimethoxybenzene 1,2
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.
- Research Organization:
- Brookhaven National Lab., Upton, N.Y.
- Sponsoring Organization:
- USDOE
- NSA Number:
- NSA-15-025948
- OSTI ID:
- 4009718
- Journal Information:
- Journal of the American Chemical Society, Journal Name: Journal of the American Chemical Society Journal Issue: 13 Vol. 83; ISSN 0002-7863
- Publisher:
- American Chemical Society (ACS)
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
Similar Records
AROMATIC HYDROGEN EXCHANGE. Annual Report No. 1, April 15, 1961 to December 31, 1961
STERIC EFFECTS AND HYDROGEN ISOTOPE EXCHANGE IN 1,2,3-TRIMETHOXYBENZENE